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Glencoe Norton Online For Your Information – History of Microcomputers

In the Beginning

In 1971, Dr. Ted Hoff puts together all the elements of a computer processor on a single silicon chip slightly larger than one square inch. The result of his efforts is the Intel 4004, the world’s first commercially available microprocessor. The chip is a 4-bit computer containing 2,300 transistors (invented in 1948) that can perform 60,000 instructions per second. Designed for use in a calculator, it sells for $200. Intel sells more than 100,000 calculators based on the 4004 chip. Almost overnight, the chip finds thousands of applications, paving the way for today’s computer-oriented world, and for the mass production of computer chips now containing millions of transistors.  1975 The first commercially available microcomputer, the Altair 880, is the first machine to be called a "personal computer." It has 64 KB of memory and an open 100-line bus structure. Selling for about $400, the Altair 880 comes in a kit to be assembled by the user. Two young college students, Paul Allen and Bill Gates, unveil the BASIC language interpreter for the Altair computer. During summer vacation, the pair form a company called Microsoft, which eventually grows into the largest software company in the world. At Bell Labs, Brian Kernighan and Dennis Ritchie develop the C programming language, which quickly becomes the most popular professional application development language.   Return to menu 1976 Steve Wozniak and Steve Jobs build the Apple I computer. It is less powerful than the Altair, but also less expensive and less complicated. Users must connect their own keyboard and video display, and have the option of mounting the computer’s motherboard in any container they choose whether a metal case, a wooden box, or a briefcase. Jobs and Wozniak form the Apple Computer Company together on April Fool’s Day, naming it after their favorite snack food. Return to menu 1977 The Apple II computer is unveiled. It comes already assembled in a case, with a built-in keyboard. Users must plug in their own TVs for monitors. Fully assembled microcomputers hit the general market, with Radio Shack, Commodore, and Apple all selling models. Sales are slow because neither businesses nor the general public know exactly what to do with these new machines. Datapoint Corporation announces Attached Resource Computing Network (ARCnet), the first commercial LAN technology intended for use with microcomputer applications. Return to menu  1978 Intel releases the 8086 microprocessor, a 16-bit chip that sets a new standard for power, capacity, and speed in microprocessors. Epson announces the MX-80 dot-matrix printer, coupling high performance with a relatively low price. (Epson from Japan sets up operations in the U.S. in 1975 as Epson America, Inc., and becomes one of the first of many foreign companies to contribute to the growth of the PC industry. Up until this point, it has been U.S. companies only. According to Epson, they gain 60 percent of the dot printer market with the MX-80.) Return to menu 1979 Intel introduces the 8088 microprocessor, featuring 16-bit internal architecture and an 8-bit external bus. Motorola introduces the 68000 chip, used in early Macintosh computers. Software Arts, Inc. releases VisiCalc, the first commercial spreadsheet program for personal computers. VisiCalc is generally credited as being the program that paved the way for the personal computer in the business world. Bob Metcalf, the developer of Ethernet, forms 3Com Corp. to develop Ethernet-based networking products. Ethernet eventually evolves into the world’s most widely used network system. MicroPro International introduces WordStar, the first commercially successful word processing program for IBM-compatible microcomputers. Return to menu  1980 IBM chooses Microsoft (co-founded by Bill Gates and Paul Allen) to provide the operating system for its upcoming PC. Microsoft purchases a program developed by Seattle Computer Products called Q-DOS (for Quick and Dirty Operating System), and modifies it to run on IBM hardware. Bell Laboratories invents the Bellmac-32, the first single-chip microprocessor with 32-bit internal architecture and a 32-bit data bus. Lotus Development Corporation unveils the Lotus 1-2-3 integrated spreadsheet program, combining spreadsheet, graphics, and database features in one package. Return to menu    1981 IBM introduces the IBM-PC, with a 4.77 MHz Intel 8088 CPU, 16 KB of memory, a keyboard, a monitor, one or two 5.25-inch floppy drives, and a price tag of $2,495. Hayes Microcomputer Products, Inc., introduces the SmartModem 300, which quickly becomes the industry standard. Xerox unveils the Xerox Star computer. Its high price eventually dooms the computer to commercial failure, but its features inspire a whole new direction in computer design. Its little box on wheels (the first mouse) can execute commands on screen (the first graphical user interface). Return to menu  1982 Intel releases the 80286, a 16-bit microprocessor. AutoCAD, a program for designing 2-D and 3-D objects, is released. AutoCAD will go on to revolutionize the architecture and engineering industries. Work begins on the development of TCP/IP. The term Internet is used for the first time to describe the worldwide network of networks that is emerging from the ARPANET.   Return to menu 1983 Time magazine features the computer as the 1982 "Machine of the Year," acknowledging the computer’s new role in society. Apple introduces the Lisa, the first commercial computer with a purely graphical operating system and a mouse. The industry is excited, but Lisa’s $10,000 price tag discourages buyers. IBM unveils the IBM-PC XT, essentially a PC with a hard disk and more memory. The XT can store programs and data on its built-in 10MB hard disk. The first version of C++ programming language is developed, allowing programs to be written in reusable independent pieces, called objects. The Compaq Portable is released, the first successful 100 percent PC-compatible clone. Despite its hefty 28 pounds, it becomes one of the first computers to be lugged through airports.   Return to menu  1984 Adobe Systems releases its PostScript system, allowing printers to produce crisp print in a number of typefaces, as well as elaborate graphic images. Apple introduces the "user-friendly" Macintosh microcomputer. IBM ships the IBM-PC AT, a 6 MHz computer using the Intel 80286 processor, which sets the standard for personal computers running DOS. IBM introduces its Token Ring networking system. Reliable and redundant, it can send packets at 4 Mbps; several years later it speeds up to16 Mbps. Satellite Software International introduces the WordPerfect word processing program. Return to menu 1985 Intel releases the 80386 processor (also called the 386), a 32-bit processor that can address more than 4 billion bytes of memory and performs ten times faster than the 80286. Aldus releases PageMaker for the Macintosh, the first desktop publishing software for microcomputers. Coupled with Apple’s LaserWriter printer and Adobe’s PostScript system, PageMaker ushers in the era of desktop publishing. Microsoft announces the Windows 1.0 operating environment, featuring the first graphical user interface for PCs. Hewlett-Packard introduces the Laser Jet laser printer, featuring 300 dpi resolution. Return to menu 1986 IBM delivers the PC convertible, IBM’s first laptop computer and the first Intel-based computer with a 3.5-inch floppy disk drive. Microsoft sells its first public stock for $21 per share, raising $61 million in the initial public offering. The First International Conference on CD-ROM technology is held in Seattle, hosted by Microsoft. Compact disks are seen as the storage medium of the future for computer users. Return to menu  1987 IBM unveils the new PS/2 line of computers, featuring a 20-MHz 80386 processor at its top end. This product line includes the MicroChannel bus, but is not a great success because consumers do not want to replace industry standard peripherals. To compete with IBM’s MicroChannel architecture, a group of other computer makers introduces the EISA (Extended Industry Standard Architecture) bus. IBM introduces its Video Graphics Array (VGA) monitor offering 256 colors at 320 x 200 resolution, and 16 colors at 640 x 480. The Macintosh II computer, aimed at the desktop publishing market, is introduced by Apple Computer. It features an SVGA monitor. Apple Computer introduced HyperCard, a programming language for the Macintosh, which uses the metaphor of a stack of index cards to represent a program—a kind of visual programming language. Motorola unveils its 68030 microprocessor. Novell introduces its network operating system, called NetWare. Return to menu  1988 IBM and Microsoft ship OS/2 1.0, the first multitasking desktop operating system. High price, a steep learning curve, and incompatibility with existing PCs contribute to its lack of market share. Apple Computer files the single biggest lawsuit in the computer industry against Microsoft and Hewlett-Packard, claiming copyright infringement of its operating system and graphical user interface. Ashton-Tate sues Fox Software and The Santa Cruz Operation, alleging copyright infringement of dBase. Hewlett-Packard introduces the first popular ink jet printer, the HP Deskjet. Steve Jobs’ new company, NeXT, Inc., unveils the NeXT computer, featuring a 25-MHz Motorola 68030 processor. The NeXT is the first computer to use object-oriented programming in its operating system and an optical drive rather than a floppy drive. Apple introduces the Apple CD SC, a CD-ROM storage device allowing access to up to 650 MB of data. A virus called the "Internet Worm" is released on the Internet, disabling about ten percent of all Internet host computers. Return to menu   1989 Intel releases the 80486 chip (also called the 486), the world’s first one-million-transistor microprocessor. The 486 integrates a 386 CPU and math coprocessor onto the same chip. Tim Berners-Lee develops software around the hypertext concept, enabling users to click on a word or phrase in a document and jump either to another location within the document or to another file. This software provides the foundation for the development of the World Wide Web, and is the basis for the first Web browsers. The World Wide Web is created at CERN, the European Particle Physics Laboratory in Geneva, Switzerland for use by scientific researchers. Microsoft’s Word for Windows introduction begins the "Microsoft Office" suite adoption by millions of users. Previously, Word for DOS had been the second-highest-selling word processing package behind Word Perfect. Return to menu 1990 Microsoft releases Windows 3.0, shipping 1 million copies in four months. A multimedia PC specification setting the minimum hardware requirements for sound and graphics components of a PC is announced at the Microsoft Multimedia Developers’ Conference. The National Science Foundation Network (NSFNET) replaces ARPANET as the backbone of the Internet. Motorola announces its 32-bit microprocessor, the 68040, incorporating 1.2 million transistors. Return to menu  1991 Apple Computer launches the PowerBook series of battery-powered portable computers. Apple, IBM, and Motorola sign a cooperative agreement to design and produce RISC-based chips, integrate the Mac OS into IBM’s enterprise systems, produce a new object-oriented operating system, and develop common multimedia standards. The result is the PowerPC microprocessor. Return to menu 1992 With an estimated 25 million users, the Internet becomes the world’s largest electronic mail network. In Apple Computer’s five-year copyright infringement lawsuit, Judge Vaughn Walker rules in favor of defendants Microsoft and Hewlett-Packard, finding that the graphical user interface in dispute is not covered under Apple’s copyrights. Microsoft ships the Windows 3.1 operating environment, including improved memory management and TrueType fonts. IBM introduces its ThinkPad laptop computer. Return to menu 1993 Mosaic, a point-and-click graphical Web browser, is developed at the National Center for Supercomputing Applications (NCSA), making the Internet accessible to those outside the scientific community. Intel, mixing elements of its 486 design with new processes, features, and technology, delivers the long-awaited Pentium processor. It offers a 64-bit data path and more than 3.1 million transistors. Apple Computer expands its entire product line, adding the Macintosh Color Classic, Macintosh LC III, Macintosh Centris 610 and 650, Macintosh Quadra 800, and the Powerbooks 165c and 180c. Apple introduces the Newton MessagePad at the Macworld convention, selling 50,000 units in the first ten weeks. Microsoft ships the Windows NT operating system. IBM ships its first RISC-based RS/6000 workstation, featuring the PowerPC 601 chip developed jointly by Motorola, Apple, and IBM. Return to menu      1994 Apple introduces the Power Macintosh line of microcomputers based on the PowerPC chip. This line introduces RISC to the desktop market. RISC was previously available only on high-end workstations. Netscape Communications releases the Netscape Navigator program, a World Wide Web browser based on the Mosaic standard, but with more advanced features. Online service providers CompuServe, America Online, and Prodigy add Internet access to their services. After two million Pentium-based PCs have hit the market, a flaw in the chip’s floating-point unit is found by Dr. Thomas Nicely. His report is made public on CompuServe. Linus Torvalds releases Linux, a freeware version of UNIX created by a worldwide collaboration of programmers who shared their work over the Internet. Return to menu 1995 Intel releases the Pentium Pro microprocessor. Motorola releases the PowerPC 604 chip, developed jointly with Apple and IBM. Microsoft releases its Windows 95 operating system with a massive marketing campaign, including prime-time TV commercials. Seven million copies are sold the first month, with sales reaching 26 million by year’s end. Netscape Communications captures more than 80 percent of the World Wide Web browser market, going from a start-up company to a $2.9 billion company in one year. A group of developers at Sun Microsystems create the Java development language. Because it enables programmers to develop applications that will run on any platform, Java is seen as the future of operating systems, applications, and the World Wide Web. Power Computing ships the first-ever Macintosh clones, the Power 100 series with a PowerPC 601 processor. Return to menu 1996 Intel announces the 200 MHz Pentium processor. U.S. Robotics releases the PalmPilot, a personal digital assistant that quickly gains enormous popularity because of its rich features and ease of use. Microsoft adds Internet connection capability to its Windows 95 operating system. Several vendors introduce Virtual Reality Modeling Language (VRML) authoring tools that provide simple interfaces and drag-and-drop editing features to create three-dimensional worlds with color, texture, motion video, and sound on the Web. The U.S. Congress enacts the Communications Decency Act as part of the Telecommunications Act of 1996. The act mandates fines of up to $100,000 and prison terms for transmission of any "comment, request, suggestion, proposal, image or other communication which is obscene, lewd, lascivious, filthy, or indecent" over the Internet. The day the law is passed, millions of Web page backgrounds turn black in protest. The law is immediately challenged on Constitutional grounds, ultimately deemed unconstitutional, and repealed. Return to menu 1997 Intel announces MMX technology, which increases the multimedia capabilities of a micro-processor. Also, Intel announces the Pentium II microprocessor. It has speeds of up to 333 MHz and introduces a new design in packaging, the Single Edge Contact (SEC) cartridge. It has more than 7.5 million transistors. AMD and Cyrix step up efforts to compete with Intel for the $1000-and-less PC market. Their competing processors are used by PC makers such as Dell, Compaq, Gateway, and even IBM. The U.S. Justice Department charges Microsoft with an antitrust lawsuit, claiming Microsoft was practicing anticompetitive behavior by forcing PC makers to bundle its Internet Explorer Web browser with Windows 95. Netscape Communications and Microsoft release new versions of their Web browser. Netscape’s Communicator 4 and Microsoft’s Internet Explorer 4 provide a full suite of Internet tools, including Web browser, newsreader, HTML editor, conferencing program, and e-mail application. Digital Video/Versatile Disk (DVD) technology is introduced. Capable of storing computer, audio, and video data, a single DVD disk can hold an entire movie. DVD is seen as the storage technology for the future, ultimately replacing standard CD-ROM technology in PC and home entertainment systems. Return to menu  1998 Microsoft releases the Windows 98 operating system. Seen mainly as an upgrade to Windows 95, Windows 98 is more reliable and less susceptible to crashes. It also offers improved Internet-related features, including a built-in copy of the Internet Explorer Web browser. The Department of Justice expands its actions against Microsoft, attempting to block the release of Windows 98 unless Microsoft agrees to remove the Internet Explorer browser from the operating system. Microsoft fights back and a lengthy trial begins in federal court, as the government attempts to prove that Microsoft is trying to hold back competitors such as Netscape. Intel releases two new versions of its popular Pentium II chip. The Pentium II Celeron offers slower performance than the standard PII, but is aimed at the $1,000-and-less PC market, which quickly embraces this chip. At the high end, the Pentium II Xeon is designed for use in high-performance workstations and server systems, and it is priced accordingly. Both chips boost Intel’s market share, reaching deeper into more vertical markets. Apple Computer releases the colorful iMac, an all-in-one system geared to a youthful market. The small, lightweight system features the new G3 processor, which outperforms Pentium II-based PCs in many respects. The iMac uses only USB connections, forcing many users to purchase adapters for system peripherals, and the computer does not include a floppy disk drive. Return to menu  1999 Intel unveils the Pentium III processor, which features 9.5 million transistors. Although the Pentium III’s performance is not vastly superior to the Pentium II, it features enhancements that take greater advantage of graphically rich applications and Web sites. A more powerful version of the chip (named Xeon) is also released, for use in higher-end workstations and network server systems. With its Athlon microprocessor, Advanced Micro Devices finally releases a Pentium-class chip that outperforms the Pentium III processor. The advance is seen as a boon for the lower-price computer market, which relies heavily on chips from Intel’s competitors. Apple Computer introduces updated versions of its popular iMac computer, including a laptop version, as well as the new G4 system, with performance rated at 1 gigaflop, meaning the system can perform more than one billion floating point operations per second. The world braces for January 1, 2000, as fears of the "Millennium Bug" come to a head. As airlines, government agencies, financial institutions, utilities, and PC owners scramble to make their systems "Y2K-compliant," some people panic, afraid that basic services will cease operation when the year changes from 1999 to 2000. Return to menu  2000 Shortly after the New Year, computer experts and government officials around the world announce that no major damage resulted from the "millennium date change," when computer clocks rolled over from 1999 to 2000. Immediately, a global debate begins to rage: had the entire "Y2K bug" been a hoax created by the computer industry, as a way to reap huge profits from people’s fears? Industry leaders defend their approach to the Y2K issue, stating that years of planning and preventive measures had helped the world avoid a global computer-driven catastrophe that could have brought the planet’s economy to a stand-still. Microsoft introduces Windows 2000 on Feb. 17. It is the biggest commercial software project ever attempted and one of the largest engineering projects of the century, involving 5345 full-time participants, over half of them engineers. The final product includes almost 30 million lines of code. On March 6, Advanced Micro Devices (AMD) announces the shipment of a 1GHz version of the Athlon processor, which will be used in PCs manufactured by Compaq and Gateway. It is the first 1GHz processor to be commercially available to the consumer PC market. Within days, Intel Corp. announces the release of a 1GHz version of the Pentium III processor. In April, U.S. District Judge Thomas Penfield Jackson rules that Microsoft is guilty of taking advantage of its monopoly in operating systems to hurt competitors and leverage better deals with its business partners. Soon after the finding, the Department of Justice recommends that the judge break Microsoft into two separate companies: one focused solely on operating systems, the other focused solely on application development. Microsoft quickly counters by offering to change a number of its business practices. The judge rules to divide the software giant into two companies. As of this writing, Microsoft is appealing the ruling.

Glossary

AMR. Audio Modem Riser. A standard for small expansion cards which are mounted on the motherboard and which provide connectors for the motherboard’s built-in sound and modem functions. Only used in very cheap PC configurations.

BIOS. Basic Input Output System. Program code which provides simple control over a hardware device.

Bus Master. A controller property, which allows a PCI device to take control over the PCI bus, so that data can be exchanged directly with RAM. CMOS. Complementary Metal-Oxide Semiconductor. Really a name for the process technology used, among other things, for CPU’s. There is a CMOS storage chip on the motherboard which contains a database of information about the motherboard and the other hardware devices. CSA. Communication Streaming Architecture. An Intel design, where the Gigabit LAN controller plugs directly into the north bridge.

DMA. Direct Memory Access. A system which allows an ISA device to move data directly to and from RAM.

DOS. Disk Operating System. A 16-bit operating system from the time before Windows. Can still be installed on any PC.

DRAM. Dynamic RAM. Storage cells which are used for standard RAM modules. Requires a constant refresh signal to remember the data.

ECC. Error Correcting Code. A type of RAM which can correct internal errors which might occur during program execution. Is used for DRAM in servers and in the CPU’s internal cache.

ECP. Enhanced Capabilities Port. One of the parallel port’s modes. Requires the use of a DMA channel.

EIDE. Enhanced IDE interface for hard disks. Also called PATA for Parallel ATA.

EPP. Enhanced Parallel Port. One of the parallel port’s faster modes. Also called ”Bi-directional”, since data can run both ways through the port.

ESCD. Extended System Configuration Data. A list of the installed PCI devices. Included in the CMOS storage.

File system. A system for organising data at the sector level on, for example, a hard disk. E.g. FAT32, NTFS.

IDE. Integrated Drive Electronics. Hard disk interface.

IrDA. Infrared Data Association. Standard for wireless data transfer over short distances using infrared light (like your TV remote control).

Local bus. A bus (e.g. the system bus) which runs synchronously with the clock frequency in a connected device.

LPC. Low Pin Count. An Intel standard which is used, among other things, for non ISA-based Super I/O chips, designed with relatively few pins.

Mode. A state which an interface or a system can work in.

Multitasking. When a system can work on several jobs at the same time.

PCI. Peripheral Component Interconnect. The traditional motherboard’s standard I/O bus.

PCI Express. New standard replacing PCI and AGP.

PIO. Programmed I/O. Protocol for IDE/EIDE interfaces.

POST. Power On Self Test. The part of the BIOS programs which tests the PC during startup.

Protected mode. The 32-bit program state which replaced real mode.

Real mode. A 16-bit state which programs were limited to working in in the first CPU’s.

Registers. Tiny, lightning fast RAM stores, built deep into the CPU. RAID. Redundant Arrays of Inexpensive Disks.

SATA. Serial ATA.

SCSI. Small Computer System Interface. An ”intelligent” expansion bus.

SRAM. Static RAM. A type of RAM which (in contrast to DRAM) can maintain its data without a refresh signal. SRAM is faster and more expensive than DRAM. SRAM is used, for example, for processor caches.

Demo…4

Hard Drive(s)

·  The physical disk

Hard disks consist of one or more magnetic plates mounted in a metal box. The standard size (as in Fig. 213) is about 10 x 14.5 x 2.5 cm, and such a device can contain hundreds of gigabytes of data. Inside the box, a number of glass or metal plates whir around at, for example, 5400 or 7200 revolutions per minute ­– these being the two most common speeds.

The read/write heads hover over the magnetic plates, and can transfer data at a tremendous speed:

One of the read/write heads, which can swing across the plates.

The actual read/write head is a tiny electromagnet. The magnet ends in a C-shaped head, the shape of which ensures that it virtually hovers above the magnetic plate. Under the read/write head are the disk tracks. These are thin rings packed with magnetic particles. These magnetic particles can be arranged in patterns of bits, which are translated into 0’s and 1’s by the electronics of the hard disk:

The data on the hard disk is created using electrical induction.

When the disk moves under the read/write head, it can either read the existing data or write new data to the disk:

·  If current is supplied to the coil, the head will become magnetic. This magnetism will reorganise the tiny magnetic bits in the track, so they represent new values. Thus data is written.

·  If the head is moved over the track without any current applied, it will gather up the magnetic pattern from the disk. This magnetism will induce current in the coil, and this “current” contains the track’s data, which is thus read.

A peek inside the hard disk reveals the magnetic plates, which have a diameter of 3½ inches.

The read/write heads are the most expensive part of the hard disk. When the disk is switched off, the heads are parked in a special area, so that they will not be damaged during transport. In Fig. 216, the cover has been removed from a hard disk, and you can see the uppermost arm with its read/write head.

Tracks and sectors

Each hard disk plate is divided into tracks. Each track is subdivided into a number of sectors, the disk’s smallest unit. A sector normally holds 512 bytes of data.

The individual files are written across a number of disk sectors (at least one), and this task is handled by the file system.

The file system is part of the operating system, which the disk has to formatted with. In Windows 98, the FAT32 file system is used. In Windows 2000/XP, you can also use NTFS. They are different systems for organising files and folder structures on the hard disk. You can read more about the file system in my guide, ”Do it yourself DOS”.

Hard disks are made of a number of disks, each side of which is divided into a large number of tracks. Each track contains numerous sectors, the smallest unit on a disk. In order to be able to use the sectors, the disk has to be formatted with a file system.

Hard disk development

New hard disk models are constantly being developed, and for each new generation, the capacity becomes greater. This is possible due to new read/write heads and magnetic plates which are more dense. When the magnetic density is increased, hard disks can be produced which have greater capacity for the same number of plates.

Another consequence of higher density is that the disks become faster, since they can transfer more data per rotation. There are simply more bits hidden in each track.

All hard disks have a certain amount of cache installed as 2 or 8 MB of fast RAM, which functions as a buffer. The cache helps ensure that the data gathered by the mechanics of the disk is optimally exploited.

The new and faster hard disks are always followed by new types of interface, since the controller principles have to be upgraded as well in order to handle the large amounts of data. At the time of writing, the fastest ATA interface is called ATA/133, but it is about to be replaced with Serial ATA (see Fig. 221).

 

 

 

The hard disk’s interface

The hard disk is managed by a controller built into the actual unit. This controller works together with a similar controller linked to the PC’s I/O bus (on the motherboard). I showed this setup in Fig. 20, in order to explain the concept of “interface”.

The interface’s job is to move data between the hard disk sectors and the I/O bus as fast as possible. It consists of:

·  A controller which controls the hard disk.

·  A controller which connects the hard disk to the motherboard.

·  A cable between the two controllers.

In the ”old days”, interfaces such as ST-506 and ESDI were used. The ATA (AT Attachment) interfaces are based on the IDE standard (Integrated Drive Electronics). The names, IDE and ATA are “owned” by Western Digital, but are used anyway in everyday language.

Host controller with two channels

The ATA interface can be seen as a bus, which is managed by a host controller. Up to four devices can be connected per host controller, and the devices connect directly to the motherboard.

The slightly unusual thing about the ATA interface is that there are two channels, which can each have two devices connected. They are called the primary and secondary channels. If two devices are connected to one channel, they have to be configured as one master and one slave device:

The ATA system’s four channels.

These four channels are standard on today’s motherboards using parallel ATA. Motherboards typically have connectors for two ATA cables, which can each connect two devices (master and slave).

These rectangular, male ATA connectors are placed in a fairly accessible location, and are used to connect the ribbon cables which fit hard disks and CD/DVD drives.

This motherboard has an extra, built-in RAID controller, so there are four ATA connectors in total. Each one can handle two devices.

Transfer speeds and protocols

There are many ATA versions. The protocol has been changed over the years, but on the whole, the products are backward compatible.

This means that you can readily connect an old CD-ROM drive which uses the PIO 3 protocol, for example, to a modern motherboard with an ATA/133 controller. The drive just won’t be any quicker as a result. The shift from parallel ATA/133 to Serial ATA is more profound. Here we use a different type of controller and new cables.

The various protocols have different transfer speeds, as shown in the table below.

Protocol	Max. theoretical transfer rate
PIO 3	13.3 MB/second
PIO 4	16.6 MB/second
Ultra DMA (ATA/33)	33 MB/second
ATA/66	66 MB/second
ATA/100	100 MB/second
ATA/133	133 MB/second
SATA	150 MB/second

The transfer speeds listed apply to the interface. Few hard disks can deliver more than 80 MB/second, but even so, it’s still good to have the fastest possible interface. If two hard disks are used on the same controller, or if disks with a large cache are used, there can be a need for big bandwidth for short periods.

ATA cables

 

 

 

 

Jumper to change between master and slave setting.

 

 

 

 

CD-ROM

The storage capacity of most CD-ROMs is about 650Mb of data. Originally CD-ROMS were read only devices, but now read/write technology has been developed.

Interface

Many CD-ROMs are interface to the computer using the ATAPI interface. This is ATA Packet Interface which is a IDE interface. This is designed for extra drives like CD-ROM’s and tape drives that connect to an ATA connector. The ATAPI interface is the standard interface for IDE controlled CD-ROMS. If your CD-ROM uses an a ATAPI interface, it should be supported by all available software. If you are using a SCSI controller, you should probably use a SCSI CD-ROM. There are two primary types of CD-ROMs today.

1. Read only
2. Read and Write CD-ROM

These are primarily available as an internally mounted drive, but can also be purchased as an external device. There are some CD-ROM drives that interface through the parallel printer port.

Speed

The primary performance concern of CD-ROM drives is their speed. Speeds are expressed in terms of 1X, 2X, 4X, which is the number of times the drive is than the standard CD-ROM reader. Of the read only type, speeds have exceeded 50X. CD-ROMS of up to 40X speeds and beyond can be purchased today for a reasonably low price.

The read/write type of CD-ROM speeds are expressed with three values. They are read, write, and rewrite. Current speeds of these devices are 32X, 10X, 4X. Currently 32X by 8X by 4X are priced reasonably at around $220. This compares to a 40X read CD-ROM drive at around $30-40. Therefore we recommend you do not rely upon your read/write CD-ROM drive for reading normal CDs especially where playing games in concerned. You could wear out your expensive CD-ROM performing read operations which costs a great deal more than a read only CD-ROM!

 

 

 

 

 

 

 

 

Motherboard The Memory Slots Yes, the motherboard is the mother of all boards on your computer. The motherboard may have a form factor of AT or ATX. We recommend you use ATX motherboards with ATX cases since this is the newer alternative and most modern microprocessors run on ATX motherboards. The motherboard holds the microprocessor, the memory, and several card slots. The memory may be SIMM sockets or DIMM sockets. The current standard is DIMM socketed memory. This is usually 168 pin 3 volt unbuffered synchronous DRAM memory. PC100 or PC133 memory is the current memory of choice. Most boards have 3 or 4 memory slots, which may, depending on the size of DIMM used, allow up or beyond 1 Gb total system memory. Most boards commonly allow 384 to 512 Mb of system RAM. The expansion bus The card slots are used to put additional cards such as video cards, sound cards, internal modems, or network cards into. Some motherboards today include video and sound without the addition of a extra card. These cards slots today are mostly PCI type card slots. When talking about cards that are plugged into a PC you are talking about the expansion bus. The expansion bus is a means of a microprocessor extending its communication ability further into the outside world. It is a data exchange means between add on cards and the microprocessor and the motherboard. There have been several types of expansion buses. ISA – Industry Standard Architecture. Used when the original 8088 8bit microprocessor based personal computers were produced. EISA – Extended ISA used when the 80286 through 80486 series microprocessors were being produced. This bus is still used but is being phased out and is almost gone today. MCI – Microchannel architecture by IBM and used mainly on IBM brand computers. PCI – Peripheral Component Interconnect. The popular expansion bus of choice. It is significantly faster than EISA. AGP – Accelerated Graphics Port. This bus is developed for fast video cards. It is currently up to 4X mode speed. The current popular expansion bus is the PCI (Peripheral Component Interconnect) bus for all cards except the graphics cards. For graphics cards, the bus of choice is AGP. Most motherboards today have one AGP slot and several PCI slots. Your expansion cards will plug into these card slots. Be sure you get cards that match the available type of slots on your motherboard. My microprocessor runs at 500Mhz and my memory runs at 100Mhz. Why? As PC technology grew, eventually the access speed of the memory could no longer keep pace with the increased speed of the microprocessors. At this point, an I/O cache was placed on the microprocessor to be a buffer between the external memory on the motherboard and the internal processor registers. The memory was set to run at a different "side bus" speed which is some fraction of the microprocessor speed. Therefore when the speed of the microprocessor is set, it is set to some multiple of the side bus speed. In the case of a 500Mhz processor and 100Mhz PC100 capable memory, that multiple is 5. Sometimes this multiple and the sidebus frequency is set using jumpers on the motherboard, or it may be set with auto detection and the BIOS. Other motherboard items Other items on your motherboard that you should be aware of are the small pin connectors that are used to connect the following controls and indicatory to your motherboard. Power supply switch. Reset switch The power on indicator. Hard drive activity indicator. In the case speaker connector.

Chipset and BIOS

One issue that will affect the operation of the motherboard is the chipset it uses and its BIOS it uses. The chipset is used to control the interface between the microprocessor and most of the devices and memory on the computer. The chipset used can have a significant affect on the performance of your system as can the overall design of the motherboard. The way to determine the best chipsets and motherboards is to read reviews and articles at various technical websites.

Your system’s BIOS is a computer program that allows your system to begin running and provides a small library fo function that your system will use to interface to various devices such as your hard drive. Some BIOS programs can limit the location on your hard drive where you can install bootable operating systems. The BIOS resides in a chip on the motherboard called a ROM chip. Usually part of this ROM can be reset or re programmed with updates. ROM that can be electrically re-written this way is called "flash" ROM.

 

 

Other storage devices

Other storage devices include:

• DVD Drive – DVD stands for Digital Video Disk. Most DVD drives use the ATAPI interface. They are available as internal or external devices. They can operate at up to 16X speeds but 8X is more common. They are primarily used for video storage but they can be used to hold audio and computer data. DVD is categorized into DVD-Video and DVD-ROM devices. The DVD-ROM device is for computer data storage.
• Zip drives – A removable cartridge storage device that may be used to store compressed data as a data back up method. A zip drive has between a 100Mb to 2G storage capacity. Cost is usually between $45 and $350. Some zip drives can also be used to read standard 3.5 inch floppy diskettes.
• Tape drive backup kits – Their capacity 3G to 40G. The cost range is from $200 to $1000.

More about DVD-ROM

There are five recordable versions of DVD-ROM. They can all can read DVD-ROM and DVD-Video discs, but different type of disc is used by each one for recording.

1. DVD-R/authoring – Can record data once.
2. DVD-R/general, – Can record data once. The capacity is 3.95 Gb or 4.7 Gb.
3. DVD-RAM – It is not compatible with current drives. It has a storage capacity of 2.58 Gb It can be rewritten about 100,000 times The discs are expected to hold data for 30 years or more.
4. DVD-RW – The capacity is 4.7 Gb. It can be rewritten about 1,000 times.
5. DVD+RW – It will become available in early 2001.

Keyboard and Mouse

Keyboard

Keyboards can range in cost from about $10 to $100. I generally stay with less expensive keyboards, but I try to avoid buying a keyboard with the large type PS/2 connector as mentioned in an earlier section. There are keyboards with a different feel or sound when key pressing is done. Some people are particular about the feel and sound. If you are, you may want to spend a little more for your keyboard. You may even want to buy it from a retail store so you can test the feel of it. There are special keyboards with extra functions on them for such things as surfing the internet.

Mouse

The mouse interface of choice is the PS/2 interface rather than the older serial interface. Using a PS/2 interface will not require the use of a serial port on your computer. There are a few types of mice available. The main choices are between:

1. Two or three buttons
2. Center sprocket wheel

The choice of two or three buttons depends on your preference and whether the software you run on your computer will support a three button mouse. If it does not support three buttons, it just means that you will not be able to use the third button. Many mice today have a sprocket wheel in the center which will allow the user to scroll up and down documents on the screen by turning the wheel. Also some mice are "ergonomic". I’m sure I misspelled that word.

Depending on features and the quality of the internal roller ball and mechanisms, a mouse can cost anywhere from $2 to $50. Or possibly you can find one in your back yard or basement for free.

Demo…3

Hardware connection types

Hardware can connect to your computer in several different ways. The most common types of hardware connections are Universal Serial Bus (USB), iLink/IEEE 1394/FireWire, Bluetooth, PC Card, PS/2, serial, and parallel. Here’s how they work:

USB

Most computers made in the last several years include multiple USB ports. USB has become the easiest and most common technique for connecting hardware to your computer. With this type of connection, you simply plug the hardware into your computer. If you need more ports, you can connect a USB hub to one of the existing ports on your computer.

iLink/IEEE 1394/FireWire

iLink (also known as IEEE 1394 or FireWire) is the highest-performance hardware connection. An iLink connection is typically used for digital video cameras and external hard disks. Most new computers include at least one iLink port. If your desktop computer does not have an iLink port, you can add an internal adapter with additional ports. To expand a portable computer, use a PC Card adapter.

Bluetooth

Bluetooth is a type of wireless connection. Many new portable computers support Bluetooth, but it is not as common in desktop computers. If your computer does not support Bluetooth, you can add a Bluetooth network adapter.

PC Card

Portable computers have PC Card slots (formerly known as PCMCIA) to support extremely small accessories, such as wireless adapters. Desktop computers do not include PC Card slots.

PS/2

PS/2 is the standard connection for your keyboard and mouse. The mouse connection is green, and the keyboard connection is purple.

Serial or parallel ports

Serial (9 pins) and parallel (25 pins) ports, the oldest connection type for external hardware accessories, are easy to connect. Typically, your software configures these connections automatically.

Internal

Some hardware accessories must be connected inside your computer’s case. There are three main connection types: PCI (used for most hardware); AGP (used for video adapters); and PCI Express (a new technology that replaces both PCI and AGP). If you are not comfortable opening your computer’s case, you should have a professional install internal hardware accessories.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Microprocessor

The microprocessor is the center of your computer. It processes instructions and communicates with outside devices, controlling most of the operation of the computer. The microprocessor usually has a large heat sink attached to it. Some microprocessors come in a package with a heat sink and a fan included as a part of the package. Other microprocessors require you to install the heat sink and fan separately. This is not a difficult problem, but can be a bit daunting when the buyer wants to make sure they get the correct parts to fit their microprocessor. Also the buyer needs to make sure they will get the motherboard that their microprocessor will work with. This section will explain some of the differences in microprocessors and ways to be sure your parts match.

Microprocessors and Mounting

The mounting method refers to the type of connection the microprocessor makes with the motherboard. The following table lists the various mounting packages and some of the well known microprocessors that are mounted for that package.

• Socket 7 – AMD K5, K6, Intel Pentium 75-200Mhz, IBM
• Socket 370 – Some Intel Celerons
• Slot 1 – Intel Pentium II, Pentium III, Some Celeron 266-533
• Slot II – Intel Xeon
• Slot A – AMD Athlon

The Socket 7 processors are becoming less popular. We recommend socket 370, through slot A microprocessors at the current time. The prices on Socket 370 microprocessors are currently very low considering the performance of the systems. I recently bought a Celeron 500Mhz microprocessor with 66Mhz sidebus for under $120 with a motherboard for $84. When buying a microprocessor, make sure you get the type of socket you think since some processors are made for different sockets such as the Celeron. Be sure of one of the following.

1. The socket type is stated at the vendors website.
2. There is a microprocessor part number stated at the vendors website that can be traced to the manufacturers website which specifies the mounting package you want.

It would be no fun to get a Slot 1 motherboard and a socket 370 Microprocessor.

Microprocessor heat sinks and fans.

Being sure you get the correct heat sink and fan for your microprocessor can be a bit daunting. Who wants to get a $300 microprocessor, and risk it with an incorrect mounting of a heatsink or fan? Who wants to find out that they have purchased the wrong heatsink for their processor and spend days or weeks trying to sort it out? My solution is to purchase the microprocessor with the heatsink in the same package. Usually you get a better warranty and return policy this way and you don’t need to worry about whether the two are compatible. I do not believe you can save enough money buying the heatsink and fan from anyone other then the vendor selling the microprocessor because of the time it takes for the additional research required and the potential trouble. The best solution to this problem is simply to buy a slot1, slot II or slot A microprocessor with the package that includes the fan and heatsink. These would be one of the Pentium II, Pentium III, Athlon, or Xeon packages. All that is required in this case is to slide the microprocessor carefully into its slot. With the exception of processors such as the Athlon which have a larger heat sink, requiring an extra plastic clip mechanism to help stabilize the heatsink, it is easier to install one of these processors than it is to install the computer’s RAM memory or a hard drive.

 

 

Computer Memory Packaging Memory chips are called DIPs which stands for Dual Inline Packages. They are black chips with pins on both sides. Some say they look like black bugs. To make memory installation easier than it was in the past, these DIP chips were places on modules. There are two main module types that memory comes packaged on today. SIMM – Single Inline Memory Module. They may have DIPs on one or both sides and will have 30 or 72 pins. Today, they normally are available in the 72 pin size which supports a 32 bit data transfer between the microprocessor and the memory. DIMM – Double Inline Memory Module. The modules have 168 pins and support a 64 bit data transfer between the microprocessor and the memory. Synchronous Dynamic Access Memory (SDRAM) is the type of memory that is found on DIMM packages. The term SDRAM describes the memory type, and the term DIMM describes the package. These modules are available in 3.3 or 5 volt types and buffered or unbuffered memory. This allows four choices of DIMM types. You should check your motherboard manual to determine the type of memory required. You should be able to find this information on the motherboard manufacturers website before buying the motherboard. The most common choice for todays motherboards is 3.3 volt unbuffered DIMMs. To install these packages, you press them into the socket on the motherboard and latch them in with a plastic latch on both sides. Normally as the memory module is pressed into place the latch will automatically latch the module in place. This is the essential knowledge required to understand enough to buy and install memory on your motherboard. The following sections give further technical details.   DRAM Access DRAM memory is is accessed in chunks called cells. Every cell contains a certain number of bits or bytes. A row, column scheme is used to specify the section being accessed. The cells are arranged similar to the following table. ROW 1, COL 1 ROW 1, COL 2 ROW 1, COL 3 ROW 1, COL 4 ROW 2, COL 1 ROW 2, COL 2 ROW 2, COL 3 ROW 2, COL 4 ROW 3, COL 1 ROW 3, COL 2 ROW 3, COL 3 ROW 3, COL 4 ROW 4, COL 1 ROW 4, COL 2 ROW 4, COL 3 ROW 4, COL 4 When the DRAM is accessed, the row, then the column address is specified. A page in memory is considered to be the memory available in the row. Types of DRAM The term DRAM stands for Dynamic Random Access Memory. There are three common types of DRAM today. FPM DRAM – Fast Page Mode DRAM. When the first memory access is done, the row or page of the memory is specified. Once this is done, FPO DRAM allows any other row of memory to be accessed without specifying the row number. This speeds up access time. EDO DRAM – Extended Data Out DRAM. This works like FPO DRAM but it holds the data valid even after strobe signals have gone inactive. This allows the microprocessor to request memory, and it does not need to wait for the memory to become valid. It can do other tasking, then come back later to get the data. SDRAM – Synchronized DRAM inputs and outputs its data synchronized to a clock that runs at some fraction of the microprocessor speed. SDRAM is the fastest of these three types of DRAM. There is a new SDRAM called DDR (Double Data Rate) SDRAM which allows data reads on both the rising and falling edge of the synchronized clock.

Another new type of DRAM is called RDRAM developed by Rambus, Inc. It uses a high bandwidth channel to transmit data at very high rates. It attempts to eliminate the time it takes to access memory. Synclink DRAM (SLDRAM) competes with RDRAM and uses 16 bank architecture rather than 4 along with other performance enhancing improvements.

 

 

 

Cache Memory

Cache memory is special memory that operates much faster than SDRAM memory. It is also more expensive. It would be impractical to use this memory for the entire system both for reasons of expense and physical board and bus channel design requirements. Cache memory lies between the microprocessor and the system RAM. It is used as a buffer to reduce the time of memory access. There are two levels to this memory called L1 (level 1) and L2 (level 2). The level 1 memory is a part of the microprocessor, and the level 2 memory is just outside the microprocessor.

 

Demo…2

Parts of a computer

In this article

·System unit

·Storage

·Mouse

·Keyboard

·Monitor

·Printer

·Speakers

·Modem

If you use a desktop computer, you might already know that there isn’t any single part called the "computer." A computer is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware. (Software, on the other hand, refers to the instructions, or programs, that tell the hardware what to do.)

The illustration below shows the most common hardware in a desktop computer system. Your system may look a little different, but it probably has most of these parts. A laptop computer has similar parts but combines them into a single notebook-sized package.

Desktop computer system

 

System unit

The system unit is the core of a computer system. Usually it’s a rectangular box placed on or underneath your desk. Inside this box are many electronic components that process information. The most important of these components is the central processing unit (CPU), or microprocessor, which acts as the "brain" of your computer. Another component is random access memory (RAM), which temporarily stores information that the CPU uses while the computer is on. The information stored in RAM is erased when the computer is turned off.

Almost every other part of your computer connects to the system unit using cables. The cables plug into specific ports (openings), typically on the back of the system unit. Hardware that is not part of the system unit is sometimes called a peripheral device or device.

System unit

Storage

Your computer has one or more disk drives—devices that store information on a metal or plastic disk. The disk preserves the information even when your computer is turned off.

Hard disk drive

Your computer’s hard disk drive stores information on a hard disk, a rigid platter or stack of platters with a magnetic surface. Because hard disks can hold massive amounts of information, they usually serve as your computer’s primary means of storage, holding almost all of your programs and files. The hard disk drive is normally located inside the system unit.

Hard disk drive

CD and DVD drives

Nearly all computers today come equipped with a CD or DVD drive, usually located on the front of the system unit. CD drives use lasers to read (retrieve) data from a CD, and many CD drives can also write (record) data onto CDs. If you have a recordable disk drive, you can store copies of your files on blank CDs. You can also use a CD drive to play music CDs on your computer.

CD

DVD drives can do everything that CD drives can, plus read DVDs. If you have a DVD drive, you can watch movies on your computer. Many DVD drives can record data onto blank DVDs.

If you have a recordable CD or DVD drive, periodically back up (copy) your important files to CDs or DVDs. That way, if your hard disk ever fails, you won’t lose your data.

 

 

Floppy disk drive

Floppy disk drives store information on floppy disks, also called floppies or diskettes. Compared to CDs and DVDs, floppy disks can store only a small amount of data. They also retrieve information more slowly and are more prone to damage. For these reasons, floppy disk drives are less popular than they used to be, although some computers still include them.

Floppy disk

Why are floppy disks "floppy"? Even though the outside is made of hard plastic, that’s just the sleeve. The disk inside is made of a thin, flexible vinyl material.

Mouse

A mouse is a small device used to point to and select items on your computer screen. Although mice come in many shapes, the typical mouse does look a bit like an actual mouse. It’s small, oblong, and connected to the system unit by a long wire that resembles a tail. Some newer mice are wireless.

Mouse

A mouse usually has two buttons: a primary button (usually the left button) and a secondary button. Many mice also have a wheel between the two buttons, which allows you to scroll smoothly through screens of information.

When you move the mouse with your hand, a pointer on your screen moves in the same direction. (The pointer’s appearance might change depending on where it’s positioned on your screen.) When you want to select an item, you point to the item and then click (press and release) the primary button. Pointing and clicking with your mouse is the main way to interact with your computer. For more information, see Using your mouse.

 

Keyboard

A keyboard is used mainly for typing text into your computer. Like the keyboard on a typewriter, it has keys for letters and numbers, but it also has special keys:

•	The function keys, found on the top row, perform different functions depending on where they are used.
•	The numeric keypad, located on the right side of most keyboards, allows you to enter numbers quickly.
•	The navigation keys, such as the arrow keys, allow you to move your position within a document or webpage.

 

Keyboard

You can also use your keyboard to perform many of the same tasks you can perform with a mouse. For more information, see Using your keyboard.

Monitor

A monitor displays information in visual form, using text and graphics. The portion of the monitor that displays the information is called the screen. Like a television screen, a computer screen can show still or moving pictures.

There are two basic types of monitors: CRT (cathode ray tube) monitors and LCD (liquid crystal display) monitors. Both types produce sharp images, but LCD monitors have the advantage of being much thinner and lighter. CRT monitors, however, are generally more affordable.

LCD monitor (left); CRT monitor (right)

Printer

A printer transfers data from a computer onto paper. You don’t need a printer to use your computer, but having one allows you to print e‑mail, cards, invitations, announcements, and other materials. Many people also like being able to print their own photos at home.

The two main types of printers are inkjet printers and laser printers. Inkjet printers are the most popular printers for the home. They can print in black and white or in full color and can produce high-quality photographs when used with special paper. Laser printers are faster and generally better able to handle heavy use.

Inkjet printer (left); laser printer (right)

Speakers

Speakers are used to play sound. They may be built into the system unit or connected with cables. Speakers allow you to listen to music and hear sound effects from your computer.

Computer speakers

 

 

 

Modem

To connect your computer to the Internet, you need a modem. A modem is a device that sends and receives computer information over a telephone line or high-speed cable. Modems are sometimes built into the system unit, but higher-speed modems are usually separate components.

Cable modem

Computer parts..Demo..1

Basic Hardware –

 

	Motherboard
		- Explanation of function. Demonstration of its parts
	Processor
		- Explanation of function. Demonstration of installation
		- Discussion of various brands of processor
		- Discussion of difference between cartridge and ZIF socket processors
	RAM
		- Explanation of function. Demonstration of installation
		- Discussion of difference between SIMM and DIMM
	Discussion of relationship between Processor, Ram, and Hard Drive
		- Explanation of terminology relating to size and speed of hardware
	Hard Drive
		- Explanation of function. Demonstration of installation
		- Discussion regarding cabling, slaving, and secondary IDE channel
		- Discussion of physical causes of data corruption and loss
	CD/DVD drive
		- Explanation of function. Demonstration of installation
		- Discussion of similarity between hard drive and CD/DVD
	Floppy Drive
		- Explanation of function. Demonstration of installation
		- Discussion of usefulness, reliability of floppies
	AGP
		- Explanation of function
	PCI, EPCI
		- Explanation of function
	ISA, EISA
		- Explanation of function
	Power Supply
		- Explanation of function. Demonstration of installation
		- Discussion of ATX, AT, and Pentium 4
		- Discussion regarding moving parts
		- Discussion regarding safety, dangers involved with electricity
	Ports on the Motherboard
		- Discussion about keyboard/mouse, serial/parallel, and video ports
		- Discussion about USB, sound, and other peripheral ports
	Keyboard
		- Explanation of function. Demonstration of installation
	Mouse
		- Explanation of function. Demonstration of installation
	Monitor
		- Explanation of function. Demonstration of installation
	Discussion of functional system
		- Demonstrations of incorrect setups, and symptoms they cause
	Introduction to the BIOS
		- Explanation of function. Demonstration of usage
		- Discussion of safety
		- Discussion of navigation and modification in the BIOS
		- Discuss common BIOS functions; temperature, wake, boot sequence
		- Saving and exiting BIOS
	Terminology to cover:
	RAM, CPU, PCI, ISA, AGP, BUS, IDE, ZIF, SIMM, DIMM, ATX, AT,
	Pentium, Intel, AMD, BIOS, ROM, Kilo, Mega, Giga, Terra, hurtz,
	bits, bytes, master, slave, jumpers, serial, parallel, USB, PS/2,
	DIN-5, DIN-6, DB-9, DB-25