IBM Personal Computer

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"IBM PC" redirects here. For IBM-like PCs in general ("clones"), see IBM PC compatible.
IBM PC (model 5150)
Type Personal computer
Released August 12, 1981
Discontinued April 2, 1987
Processor Intel 8088 @ 4.77 MHz
Memory 16 kB ~ 640 kB
Operating system IBM BASIC / PC-DOS 1.0
CP/M-86
UCSD p-System

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981. It was created by a team of engineers and designers under the direction of Don Estridge of the IBM Entry Systems Division in Boca Raton, Florida.

The term "personal computer" was common currency before 1981, and was used as early as 1972 to characterize Xerox PARC's Alto. However, because of the success of the IBM PC, what had been a generic term sometimes meant specifically a microcomputer compatible with IBM's products. .

Contents

[edit] Concept

The original PC was an IBM attempt to get into the small computer market then dominated by the Commodore PET, Atari 8-bit family, Apple II and Tandy Corporation's TRS-80s, and various CP/M machines.[1] IBM's first desktop microcomputer was the IBM 5100 introduced in 1975, but its price was high compared to microprocessor-based computers.

Rather than going through the usual IBM design process, a special team was assembled with authorization to bypass normal company restrictions and get something to market rapidly. This project was given the code name Project Chess.

The team consisted of twelve people headed by Don Estridge and Chief Scientist Larry Potter. They developed the PC in about a year. To achieve this they first decided to build the machine with "off-the-shelf" parts from a variety of different original equipment manufacturers (OEMs) and countries. Previously IBM had developed their own components. Secondly, they decided on an open architecture so that other manufacturers could produce and sell peripheral components and compatible software. IBM also sold an IBM PC Technical Reference Manual which included a listing of the ROM BIOS source code.[2]

At the time, Don Estridge and his team considered using the IBM 801 processor and its operating system that had been developed at the Thomas J. Watson Research Center in Yorktown Heights, New York (The 801 is an early RISC microprocessor designed by John Cocke and his team at Yorktown Heights.) The 801 was at least an order of magnitude more powerful than the Intel 8088, and the operating system many years more advanced than the DOS operating system from Microsoft, that was finally selected. Ruling out an in-house solution made the team’s job much easier and may have avoided a delay in the schedule, but the ultimate consequences of this decision for IBM were far-reaching. IBM had recently developed the Datamaster business microcomputer which used an Intel processor and peripheral ICs; familiarity with these chips and the availability of the Intel 8088 processor was a deciding factor in the choice of processor for the new product. Even the 62-pin expansion bus slots were designed to be similar to the Datamaster slots. Delays due to in-house development of the Datamaster software also influenced the design team to a fast track development process for the PC, with publicly-available technical information to encourage third-party developers. [3]

Other manufacturers soon reverse engineered the BIOS to produce their own non-infringing functional copies. Columbia Data Products introduced the first IBM-PC compatible computer in June 1982. In November 1982, Compaq Computer Corporation announced the Compaq Portable, the first portable IBM PC compatible. The first models were shipped in March 1983.

Once the IBM PC became a commercial success the PC came back under the usual IBM management control, with the result that competitors had little trouble taking the lead from them. (In this regard, IBM's tradition of "rationalizing" their product lines—deliberately restricting the performance of lower-priced models in order to prevent them from "cannibalizing" profits from higher-priced models—worked against them).

[edit] Third-party distribution

Sears Roebuck and Computerland executives were involved with the IBM team from the start. The IBMers - especially H.L. ('Sparky') Sparks, who was in charge of sales and marketing - relied on them for much of their knowledge of the marketplace. In turn, almost by default, they were to become the main outlets for the new product. Sears Roebuck would set up a handful of computer centers. Most importantly, more than 190 Computerland stores already existed. From IBM's point of view, this meant that there would be immediate widespread distribution across the US. In the event, Sears Roebuck failed to live up to expectations, when the new PC turned out to be selling to the office market rather than the home - where it had originally been targeted.

[edit] Models

The models of IBM's first-generation Personal Computer (PC) series have the following names:

The original PC had a version of Microsoft BASIC —IBM Cassette BASIC— in ROM. The CGA (Color Graphics Adapter) video card could use a standard television for display; the other option that was offered by IBM is a MDA (Monochrome Display Adapter) and a monochrome display model 5151. The standard storage device is cassette tape. A floppy disk drive was an optional extra; no factory-installed hard disk was available. It has only five expansion slots; maximum memory using IBM parts is 256 kB (256 KiB) , 64 kB on the main board and three 64 kB expansion cards. The processor is an Intel 8088 (early 1978 version, later were 1978/81/2 versions of intel chip, second-sourced AMDs were used after 1983) running at 4.77 MHz (4/3 the standard NTSC color burst frequency of 3.579545 MHz), which could be replaced with a NEC V20 for a slight increase in processing speed. An Intel 8087 co-processor could also be added for enhanced mathematical processing power. IBM sold it in configurations with 16 kB or 64 kB of RAM preinstalled using either nine or thirty-six 16-kbit (16-Kibit) DRAM chips. (As was common at the time, an extra bit is used for parity checking of memory.) The IBM 5161 Expansion Chassis was eventually released and allowed for more expansion boards to be installed as well as additional hard drives.

Although the TV-compatible video board, cassette port and FCC Class B certification were all aimed at making it a home computer [4] the original PC proved too expensive for the home market. At introduction a PC with 64 kB of RAM and a single 5 1/4 inch floppy drive sold for US $3000. [5] [6]It was an unexpectedly large success with businesses. The "IBM Personal Computer XT" is an enhanced machine that was designed for business use. It has 8 expansion slots and a 10 megabyte hard disk. It can take 256 kB of memory on the main board (using 64 kbit DRAM); later models are expandable to 640 kB. (The 384 kB of BIOS ROM, video RAM, and adapter ROM space filled the rest of the one megabyte address space of the 8088 CPU.) It was usually sold with a Monochrome Display Adapter (MDA) video card. The processor is a 4.77 MHz Intel 8088 and the expansion bus 8-bit Industry Standard Architecture (ISA) with XT bus architecture.

The "IBM Personal Computer/AT", announced August 1984, uses an Intel 80286 processor, originally at 6 MHz. It has a 16-bit ISA bus and 20 MB (20 million bytes) hard drive. A faster model, running at 8 MHz, was introduced in 1986. IBM made some attempt at marketing it as a multi-user machine, but it sold mainly as a faster PC for power users. Early PC/ATs were plagued with reliability problems, in part because of some software and hardware incompatibilities, but mostly related to the internal 20 MB hard disk. While some people blamed IBM's hard disk controller card and others blamed the hard disk manufacturer Computer Memories Inc. (CMI), the IBM controller card worked fine with other drives, including CMI's 33-megabyte model. The problems introduced doubt about the computer and, for a while, even about the 286 architecture in general, but after IBM replaced the 20 MB CMI drives, the PC/AT proved reliable and became a lasting industry standard.

All IBM personal computers are software compatible with each other in general, but not every program will work in every machine. Some programs are time sensitive to a particular speed class. Older programs will not take advantage of newer higher-resolution display standards.

The IBM PC range
Model name Model # Introduced CPU Features
PC 5150 Aug 1981 8088 Floppy disk system
XT 5160 Mar 1983 8088 First IBM PC with a "hard drive"
XT/370 5160/588 Oct 1983 8088 System/370 mainframe emulation
3270 PC 5271 Oct 1983 8088 With 3270 terminal emulation
PCjr 4860 Nov 1983 8088 Floppy-based home computer
PC Portable 5155 Feb 1984 8088 Floppy-based portable
AT 5170 Aug 1984 80286 Medium-speed hard disk
Convertible 5140 Apr 1986 8088 Microfloppy laptop portable
XT 286 5162 Sep 1986 80286 Slow hard disk, but zero wait state memory on the motherboard. This 6 MHz machine was actually faster than the 8 MHz ATs (when using planar memory) because of the zero wait states

[edit] Technology

[edit] Electronics

The main circuit board in an IBM PC is called the motherboard (IBM terminogy calls it a planar). This carries the CPU and memory, and has a bus with slots for expansion cards.

The bus used in the original PC became very popular, and was subsequently named ISA. It is in use to this day in computers for industrial use. Later, requirements for higher speed and more capacity forced the development of new versions. IBM introduced the MCA bus with the PS/2 line. The VESA Local Bus allowed for up to three, much faster 32-bit cards, and the EISA architecture was developed as a backward compatible standard including 32-bit card slots, but it only sold well in high-end server systems. The lower-cost and more general PCI bus was introduced in 1994 and has now become ubiquitous.

The motherboard is connected by cables to internal storage devices such as hard disks, floppy disks and CD-ROM drives. These tend to be made in standard sizes, such as 3.5" (90 mm) and 5.25" (133.4 mm) widths, with standard fixing holes. The case also contains a standard power supply unit (PSU) which is either an AT or ATX standard size.

Intel 8086 and 8088-based PCs require expanded memory (EMS) boards to work with more than one megabyte of memory. The original IBM PC AT used an Intel 80286 processor which can access up to 16 megabytes of memory (though standard DOS applications cannot use more than one megabyte without using additional APIs.) Intel 80286-based computers running under OS/2 can work with the maximum memory.

[edit] Keyboard

The original 1981 IBM PC's keyboard at the time was an extremely reliable and high quality keyboard originally developed in North Carolina for the Datamaster system [7]. Each key was rated to be reliable to over 100 million keystrokes. Compared to the keyboards of other small computers at the time, the IBM PC keyboard was far superior and played a significant role in establishing a high quality impression. Byte magazine in the fall of 1981 went so far as to state that the keyboard was 50 percent of the reason to buy an IBM PC. The importance of the keyboard was definitely established when the IBM PCjr flopped, in very large part for having a much different and mediocre Chiclet keyboard that made a poor impression on customers. Oddly enough, the same thing almost happened to the IBM PC when in early 1981 management seriously considered substituting a cheaper but lower quality keyboard. This mistake was narrowly avoided by the advice of one of the original development engineers.

However, the original 1981 IBM PC's keyboard was severely criticized by typists for its non-standard placement of the return and left shift keys. In 1984, IBM corrected this on its AT keyboard, but shortened the backspace key, making it harder to reach. In 1987, it introduced the enhanced keyboard, which relocated all the function keys and the Ctrl keys. The Esc key was also relocated to the opposite side of the keyboard.

Another criticism of the original keyboard was the relatively loud "clack" sound each key made when pressed. Since typewriter users were accustomed to keeping their eyes on the hardcopy they were typing from and had come to rely on the sound that was made as each character was typed onto the paper to ensure that they had pressed the key hard enough (and only once), the PC keyboard "clack" feature was intended to provide that same reassurance. However, it proved to be very noisy and annoying, especially if many PCs were in use in the same room, and later keyboards were significantly quieter.

An "IBM PC compatible" may have a keyboard that does not recognize every key combination a true IBM PC does, such as shifted cursor keys. In addition, the "compatible" vendors sometimes used proprietary keyboard interfaces, preventing the keyboard from being replaced.

Although the PC/XT and AT used the same style of keyboard connector, the low-level protocol for reading the keyboard was different between these two series. An AT keyboard could not be used in an XT, nor the reverse. Third-party keyboard manufacturers provided a switch to select either AT-style or XT-style protocol for the keyboard.

See also: Keyboard layout

[edit] Serial port addresses and interrupts

COM Port IRQ Base Port Address
COM1 IRQ4 3F8H
COM2 IRQ3 2F8H
COM3 IRQ4 3E8H
COM4 IRQ3 2E8H

Only COM1: and COM2: addresses were defined by the original PC. Attempts to share IRQ 3 and IRQ4 to use additional ports require special measures in hardware and software, since shared IRQs were not defined in the original PC design.

[edit] Character set

The original IBM PC used the 7-bit ASCII alphabet as its basis, but extended it to 8 bits with nonstandard character codes. This character set was not suitable for some international applications, and soon a veritable cottage industry emerged providing variants of the original character set in various national variants. In IBM tradition, these variants were called code pages. These codings are now obsolete, having been replaced by more systematic and standardized forms of character coding, such as ISO 8859-1, Windows-1251 and Unicode. The original character set is known as Code page 437.

[edit] Storage media

5 1/4 inch Diskette Drive with a partially inserted double-density diskette containing DOS 1.1.
5 1/4 inch Diskette Drive with a partially inserted double-density diskette containing DOS 1.1.

Originally, the only storage medium for the original IBM PC model 5150 was a port for connection to a cassette drive. This was not the sort of unit expected in such an expensive computer and it was seldom used; few (if any) IBM PCs left the factory without a floppy disk drive installed. The 1981 PC had one or two 160 kilobyte 5¼ inch single-sided double-density floppy disk drives (180 kilobyte in later MS-DOS versions).[8] XTs generally had one double-sided 360 kB drive (next to the hard disk).

The first IBM PC that included a fixed, non-removable, hard disk was the XT. Hard disks for IBM compatibles soon became available with very large storage capacities. If a hard disk was added that was not compatible with the existing disk controller, a new controller board had to be plugged in; some disks were integrated with their controller in a single expansion board, commonly called a "Hard Card".

In 1984, IBM introduced the 1.2 megabyte dual sided floppy disk along with its AT model. Although often used as backup storage, the high density floppy was not often used by software manufacturers for interchangeability. In 1986, IBM began to use the 720 kB double density 3.5" microfloppy disk on its Convertible laptop computer. It introduced the so-called "1.44 MB" high density version with the PS/2 line.[9] These disk drives could be added to existing older model PCs. In 1988 IBM introduced a drive for 2.88 MB "DSED" diskettes in its top-of-the-line PS/2 models; it was an instant failure and is all but forgotten today (but survives as a possible "size" choice in disk-formatting utilities).

[edit] Original software

All IBM PCs include a relatively small piece of software stored in ROM. The original IBM PC 40 KB ROM included 8 KB for power-on self-test (POST) and basic input/output system (BIOS) functions plus 32 KB BASIC in ROM (Cassette BASIC). The ROM BASIC interpreter was the default user interface if no DOS boot disk was present. BASICA was distributed on floppy disk and provided a way to run the ROM BASIC under PC-DOS control.

In addition to PC-DOS, buyers could choose either CP/M-86 or UCSD p-System as operating systems. Due to their higher prices, they never became very popular and PC-DOS or MS-DOS came to be the dominant operating system.

[edit] Longevity

While the IBM PC technology is largely obsolete by today's standards, many are still in service. As of June 2006, IBM PC and XT models are still in use at the majority of U.S. National Weather Service upper-air observing sites. The computers are used to process data as it is returned from the ascending radiosonde, attached to a weather balloon. They are being phased out over a several year period, to be replaced by the Radiosonde Replacement System.

[edit] See also

[edit] Notes

  1. ^ "Total share: 30 years of personal computer market share figures", Jeremy Reimer Dec.14, 2005 http://arstechnica.com/articles/culture/total-share.ars/4
  2. ^ Charlie Anderson (2003-11-13). The Virtual PC Museum. Charlie Anderson. Retrieved on 2006-12-16.. Personal website with an image of the technical manual. "The official documentation came in cool three-ring binders, complete with slip covers. Completely typeset.... This book wasn't free, either—I think it cost $60. Supposedly, no Compaq BIOS programmer ever saw one of these. Yeah, right." Jargon File 3.0.0—TechRef. Jargon File, TechRef: /tek'ref/ [MS-DOS] n. The original "IBM PC Technical Reference Manual", including the BIOS listing and complete schematics for the PC. The only PC documentation in the issue package that's considered serious by real hackers."
  3. ^ David J. Bradley, The Creation of the IBM PC, BYTE Magazine Volume 15 No. 9 September 1990 pages 414-420
  4. ^ David J. Bradley The Creation of the IBM PC, BYTE,ISSN 0360-5280/09,Volume 15, Number 9, September 1990 pp. 414-420
  5. ^ http://www.tmworld.com/article/CA187350.html Whence Came the IBM PC Test and Measurement World retrieved 2008 03 02
  6. ^ Gene Smart and Andrew Reinhardt, 15 years of Bits, Bytes and Other Great Moments, BYTE Magazine, September 1990 pg. 382
  7. ^ David Bradley, BYTE Sept. 1990
  8. ^ IBM (July 1982). Technical Reference: Personal Computer Hardware Reference Library, Revised Edition, IBM Corp., page 2-93. 6025008.  The drives are soft sectored, single or double sided, with 40 tracks per side. They are Modified Frequency Modulation (MFM) coded in 512 byte sectors, giving a formatted capacity of 163,840 bytes per drive for single sided and 327,680 bytes per drive for double sided.
  9. ^ The actual storage capacity of these floppy disks was 1440×1024 B

[edit] References

  • Norton, Peter (1986). Inside the IBM PC. Revised and enlarged. New York. Brady. ISBN 0-89303-583-1.
  • August 12, 1981 press release announcing the IBM PC (PDF format).
  • Mueller, Scott (1992). Upgrading and Repairing PCs, Second Edition, Que Books, ISBN 0-88022-856-3
  • Chposky, James; Ted Leonsis (1988). Blue Magic - The People, Power and Politics Behind the IBM Personal Computer. Facts On File. ISBN 0-8160-1391-8. 
  • IBM (1983). Personal Computer Hardware Reference Library: Guide to Operations, Personal Computer XT. IBM Part Number 6936831.
  • IBM (1984). Personal Computer Hardware Reference Library: Guide to Operations, Portable Personal Computer. IBM Part Numbers 6936571 and 1502332.
  • IBM (1986). Personal Computer Hardware Reference Library: Guide to Operations, Personal Computer XT Model 286. IBM Part Number 68X2523.
  • This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

[edit] External links

IBM PC Series
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