IBM PC COMPATIBLE computers are those similar to the original IBM PC , XT , and AT , able to run the same software and support the same expansion cards as those. Such computers used to be referred to as PC CLONES, or IBM CLONES. They duplicate almost exactly all the significant features of the PC architecture, facilitated by IBM's choice of commodity hardware components and various manufacturers' ability to reverse engineer the BIOS firmware using a "clean room design " technique. Columbia Data Products built the first clone of the IBM personal computer by a clean room implementation of its BIOS.
Early IBM PC compatibles used the same computer bus as the original PC and AT models. The IBM AT compatible bus was later named the Industry Standard Architecture bus by manufacturers of compatible computers. The term "IBM PC compatible" is now a historical description only, since IBM has ended its personal computer sales.
Descendants of the IBM PC compatibles comprise the majority of
personal computers on the market presently with the dominant operating
* 1 Origins
* 2 Compatibility issues
* 2.1 Non-compatible MS-DOS computers * 2.2 "Operationally Compatible"
* 3 The decreasing influence of IBM
* 4 Expandability
* 5 "IBM PC compatible" becomes "Wintel"
* 6 Design limitations and more compatibility issues
* 7 Challenges to
* 8 The
IBM PC compatible
The original IBM PC (Model 5150) motivated the production of clones during the early 1980s.
IBM decided in 1980 to market a low-cost single-user computer as
quickly as possible in response to Apple Computer 's success in the
burgeoning microcomputer market. On 12 August 1981, the first IBM PC
went on sale. There were three operating systems (OS) available for
it. The least expensive and most popular was
PC DOS made by Microsoft
. In a crucial concession, IBM's agreement allowed
IBM at first asked developers to avoid writing software that addressed the computer's hardware directly, and to instead make standard calls to BIOS functions that carried out hardware-dependent operations. This software would run on any machine using MS-DOS or PC-DOS. Software that directly addressed the hardware instead of making standard calls was faster, however; this was particularly relevant to games. Software addressing IBM PC hardware in this way would not run on MS-DOS machines with different hardware. The IBM PC was sold in high enough volumes to justify writing software specifically for it, and this encouraged other manufacturers to produce machines which could use the same programs, expansion cards , and peripherals as the PC. The 808x computer marketplace rapidly excluded all machines which were not hardware- and software-compatible with the PC. The 640 KB barrier on "conventional" system memory available to MS-DOS is a legacy of that period; other non-clone machines, while subject to a limit, could exceed 640 kB.
Rumors of "lookalike", compatible computers, created without IBM's approval, began almost immediately after the IBM PC's release. InfoWorld wrote on the first anniversary of the IBM PC that
The dark side of an open system is its imitators. If the specs are clear enough for you to design peripherals, they are clear enough for you to design imitations. Apple ... has patents on two important components of its systems ... IBM, which reportedly has no special patents on the PC, is even more vulnerable. Numerous PC-compatible machines—the grapevine says 60 or more—have begun to appear in the marketplace.
By June 1983
NON-COMPATIBLE MS-DOS COMPUTERS
At the same time, many manufacturers such as Tandy /
Tandy described the Tandy 2000 , for example, as having a "'next generation' true 16-bit CPU", and with "More speed. More disk storage. More expansion" than the IBM PC or "other MS-DOS computers". While admitting in 1984 that many MS-DOS programs did not support the computer, the company stated that "the most popular, sophisticated software on the market" was available, either immediately or "over the next six months".
Like IBM, Microsoft's intention was that application writers would write to the application programming interfaces in MS-DOS or the firmware BIOS, and that this would form what would now be termed a hardware abstraction layer . Each computer would have its own Original Equipment Manufacturer (OEM) version of MS-DOS, customized to its hardware. Any software written for MS-DOS would operate on any MS-DOS computer, despite variations in hardware design.
This expectation seemed reasonable in the computer marketplace of the
time. Until then
Microsoft's competing OS was intended initially to operate on a similar varied spectrum of hardware, although all based on the 8086 processor. Thus, MS-DOS was for several years sold only as an OEM product. There was no Microsoft-branded MS-DOS: MS-DOS could not be purchased directly from Microsoft, and each OEM release was packaged with the trade dress of the given PC vendor. Malfunctions were to be reported to the OEM, not to Microsoft. However, as machines that were compatible with IBM hardware—thus supporting direct calls to the hardware—became widespread, it soon became clear that the OEM versions of MS-DOS were virtually identical, except perhaps for the provision of a few utility programs.
MS-DOS provided adequate functionality for character-oriented
applications such as those that could have been implemented on a
text-only terminal . Had the bulk of commercially important software
been of this nature, low-level hardware compatibility might not have
mattered. However, in order to provide maximum performance and
leverage hardware features (or work around hardware bugs), PC
applications quickly developed beyond the simple terminal applications
MS-DOS supported directly. Spreadsheets ,
MS-DOS itself did not provide any way to position the text cursor
other than to advance it after displaying each letter (teletype mode
). While the
BIOS video interface routines were adequate for
rudimentary output, they were necessarily less efficient than direct
hardware addressing, as they added extra processing; they did not have
"string" output, but only character-by-character teletype output, and
they inserted delays to prevent CGA hardware "snow" (a display
artifact of CGA cards produced when writing directly to screen
memory)——an especially bad artifact since they were called by IRQs
, thus making multitasking very difficult. A program that wrote
directly to video memory could achieve output rates 5 to 20 times
faster than making system calls .
Turbo Pascal used this technique
from its earliest versions.
* Graphics capability was not taken seriously in the original IBM
design brief; graphics were considered only from the perspective of
generating static business graphics such as charts and graphs. MS-DOS
did not have an API for graphics, and the
BIOS only included the
rudimentary graphics functions such as changing screen modes and
plotting single points. To make a
BIOS call for every point drawn or
modified increased overhead considerably, making the
notoriously slow. Because of this, line-drawing , arc-drawing, and
blitting had to be performed by the application to achieve acceptable
speed, which was usually done by bypassing the
BIOS and accessing
video memory directly. Software written to address IBM PC hardware
directly would run on any IBM clone, but would have to be rewritten
especially for each non-PC-compatible
* Video games , even early ones, mostly required a true graphics
mode. They also performed any machine-dependent trick the programmers
could think of in order to gain speed. Though initially the major
market for the PC was for business applications, games capability
became an important factor motivating PC purchases as prices
decreased. The availability and quality of games could mean the
difference between the purchase of a PC compatible or a different
platform with the ability to exchange data like the
PC compatibility was an important concern. Even the Commodore
In May 1983, Future Computing defined four levels of compatibility:
* Operationally Compatible. Can run "the top selling" IBM PC
software, use PC expansion boards, and read and write PC disks. Has
"complementary features" like portability or lower price that
distinguish computer from the PC, which is sold in the same store.
Examples: (Best) Columbia Data Products, Compaq; (Better) Corona;
* Functionally Compatible. Runs own version of popular PC software.
Cannot use PC expansion boards but can read and write PC disks. Cannot
become Operationally Compatible. Example: TI Professional .
* Data Compatible. May not run top PC software. Can read and/or
write PC disks. Can become Functionally Compatible. Examples: NCR
Compaq engineers found that
Many companies were reluctant to have their products' PC
compatibility tested. When
Creative Computing in 1985 stated, "we reiterate our standard line regarding the IBM PC compatibles: try the package you want to use before you buy the computer." Companies modified their computers' BIOS to work with newly discovered incompatible applications, and reviewers and users developed stress tests to measure compatibility; by 1984 the ability to operate Lotus 1-2-3 and Flight Simulator became the standard, with compatibles specifically designed to run them.
IBM believed that some companies such as Eagle, Corona, and Handwell infringed on its copyright, and after Apple Computer, Inc. v. Franklin Computer Corp. successfully forced the clone makers to stop using the BIOS. The Phoenix BIOS in 1984, however, and similar products such as AMI BIOS , permitted computer makers to legally build essentially 100%-compatible clones without having to reverse-engineer the PC BIOS themselves. A September 1985 InfoWorld chart listed seven compatibles with 256 KB RAM, two disk drives, and monochrome monitors for $1,495 to $2,320, while the equivalent IBM PC cost $2,820. By 1986 Compute! stated that "clones are generally reliable and about 99 percent compatible".
THE DECREASING INFLUENCE OF IBM
In February 1984 Byte wrote that "IBM's burgeoning influence in the
PC community is stifling innovation because so many other companies
are mimicking Big Blue", but as the market grew IBM's influence
diminished. In November 1985
After IBM announced the OS/2 -oriented PS/2 line in early 1987, sales of existing DOS-compatible PC compatibles rose, in part because the proprietary operating system was not available. In 1988 Gartner Group estimated that the public purchased 1.5 clones for every IBM PC. By 1989 Compaq was so influential that industry executives spoke of " Compaq compatible", with observers stating that customers saw the company as IBM's equal.
After 1987, IBM PC compatibles dominated both the home and business
markets of commodity computers, with other notable alternative
architectures being used in niche markets, like the Macintosh
computers offered by
* IBM designed the PC with an open architecture which permitted
clone makers to use freely available non-proprietary components.
No mass-market personal computer hardware vendor dared to be
incompatible with the latest version of Windows, and Microsoft's
annual WinHEC conferences provided a setting in which
This terminology itself is becoming a misnomer, as Intel has lost
absolute control over the direction of x86 hardware development with
DESIGN LIMITATIONS AND MORE COMPATIBILITY ISSUES
Although the IBM PC was designed for expandability, the designers
could not anticipate the hardware developments of the 1980s, nor the
size of the industry they would engender. To make things worse, IBM's
choice of the
"Expanded" and "extended" memory have incompatible interfaces, so anyone writing software that used more than one megabyte had to provide for both systems for the greatest compatibility until MS-DOS began including EMM386, which simulated EMS memory using XMS memory. A protected mode OS can also be written for the 80286, but DOS application compatibility was more difficult than expected, not only because most DOS applications accessed the hardware directly, bypassing BIOS routines intended to ensure compatibility, but also that most BIOS requests were made by the first 32 interrupt vectors, which were marked as "reserved" for protected mode processor exceptions by Intel.
Video cards suffered from their own incompatibilities. Once video
cards advanced to
SVGA the standard for accessing them was no longer
clear. At the time, PC programming used a memory model that had 64 KB
memory segments . The most common
When the 386 was introduced, again a protected mode OS could be written for it. This time, DOS compatibility was much easier because of virtual 8086 mode . Unfortunately programs could not switch directly between them, so eventually, some new memory-model APIs were developed, VCPI and DPMI , the latter becoming the most popular.
Because of the great number of third-party adapters and no standard for them, programming the PC could be difficult. Professional developers would operate a large test-suite of various known-to-be-popular hardware combinations.
Meanwhile, consumers were overwhelmed by the competing, incompatible standards and many different combinations of hardware on offer. To give them some idea of what sort of PC they would need to operate their software, the Multimedia PC (MPC) standard was set during 1990. A PC that met the minimum MPC standard could be marketed with the MPC logo, giving consumers an easy-to-understand specification to look for. Software that could operate on the most minimally MPC-compliant PC would be guaranteed to operate on any MPC. The MPC level 2 and MPC level 3 standards were set later, but the term "MPC compliant" never became popular. After MPC level 3 during 1996, no further MPC standards were established.
CHALLENGES TO WINTEL DOMINATION
By the late 1990s, the success of
Very early on in PC history, some companies introduced their own
XT-compatible chipsets . For example, Chips and Technologies
Companies such as
A major alternative to
Wintel domination is the rise of mobile
computing since the early 2000s, which has been marked as the start of
a post-PC era . By mid-2016, Windows-running PCs had a little less
than half the market share of all computers; but all such "IBM PC"
compatibles with the additional macOS -running computers, that are
also capable of running Windows, "PCs" had at that point a slight
majority. Mobile computers, running Android and iOS – Tablets and
smartphones – based on CPUs with the
THE IBM PC COMPATIBLE TODAY
See also: Legacy-free PC
The term "IBM PC compatible" is not commonly used presently because
all current mainstream desktop and laptop computers are based on the
PC architecture, and IBM no longer makes PCs. The competing hardware
architectures have either been discontinued or, like the
The processor speed and memory capacity of modern PCs are many orders of magnitude greater than they were for the original IBM PC and yet backwards compatibility has been largely maintained – a 32-bit operating system released during the 2000s can still operate many of the simpler programs written for the OS of the early 1980s without needing an emulator , though an emulator like DOSBox now has near-native functionality at full speed. Additionally, many modern PCs can still run DOS directly, although special options such as USB legacy mode and SATA-to-PATA emulation may need to be set in the BIOS setup utility. Computers using the Extensible Firmware Interface might need to be set at legacy BIOS mode to be able to boot DOS. However, the BIOS/EFI options in most mass-produced consumer-grade computers are very limited and cannot be configured to truly handle OSes such as the original variants of DOS.
The recent spread of the x86-64 architecture has further distanced
current computers' and operating systems' internal similarity with the
original IBM PC by introducing yet another processor mode with an
instruction set modified for 64-bit addressing, but x86-64 capable
processors also retain standard x86 compatibility. Intel started
making x86 CPUs (
AT (form factor)
ATX form factor
Baby AT form factor
* ^ Norton, Peter (5 February 1985). "Software for Once and All". PC Magazine. p. 103. Retrieved 28 October 2013. * ^ Libes, Sol (December 1981). "Bytelines". BYTE. pp. 314–318. Retrieved 29 January 2015. * ^ "Lookalikes From Home & Abroad". PC Magazine. February–March 1982. p. 5. Retrieved 20 October 2013. * ^ Zussman, John Unger (1982-08-23). "Let\'s keep those systems open". InfoWorld. p. 29. Retrieved 29 January 2015. * ^ Sandler, Corey (June 1983). "Getting To Know You". PC Magazine. p. 31. Retrieved 21 October 2013. * ^ A B Mace, Scott (9–16 January 1984). "IBM PC clone makers shun total compatibility". InfoWorld. pp. 79–81. Retrieved 4 February 2015. * ^ Cook, Karen; Langdell, James (24 January 1984). "PC-Compatible Portables". PC Magazine. p. 39. Retrieved 23 October 2013. * ^ "Radio Shack Computer Catalog RSC-12, page 4". radioshackcatalogs dot com. Tandy/Radio Shack. Retrieved June 27, 2017. * ^ "Radio Shack Computer Catalog RSC-11, page 6". radioshackcatalogs dot com. Tandy/Radio Shack. Retrieved June 27, 2017. * ^ A B C Pournelle, Jerry (November 1984). "NCC Reflections". BYTE. p. 361. Retrieved 23 October 2013. * ^ Ward, Ronnie (November 1983). "Levels of PC Compatibility". BYTE. pp. 248–249. Retrieved 19 March 2016. * ^ A B Yakal, Kathy (January 1985). " Bruce Artwick / The Designer Behind Flight Simulator II". Compute!'s Gazette. p. 32. Retrieved 6 July 2014. * ^ Alsop, Stewart (31 January 1994). "A public Windows pane to make compatibility clearer". InfoWorld. p. 102. Retrieved 28 February 2011. * ^ da Cruz, Frank (1984-01-23). "IBM PC Kermit" . Info-Kermit Digest (Mailing list). Kermit Project, Columbia University. Retrieved 23 February 2016. * ^ Krasnoff, Barbara (20 March 1984). "No Matter Who\'s Invited, Some Will Turn Out To Be Incompatible". PC Magazine. p. 57. Retrieved 24 October 2013. * ^ Krasnoff, Barbara (3 April 1984). "Putting PC Compatibles To the Test". PC Magazine. pp. 110–144. Retrieved 24 October 2013. * ^ "Pick Up Where IBM Leaves Off.". InfoWorld (advertisement). 1984-02-27. p. 41. Retrieved 18 January 2015. * ^ Malloy, Rich (September 1983). "The Corona Portable PC". BYTE. pp. 226–228. Retrieved 16 August 2015. * ^ A B Pournelle, Jerry (July 1984). "The West Coast Faire". Byte . p. 136. Retrieved November 8, 2011. * ^ A B Lockwood, Russ (September 1985). "Zenith Z-151; choice of U.S. Air Force and Navy". Creative Computing. p. 50. Retrieved 26 February 2013. * ^ Poor, Alfred (2 October 1984). "Zenith Strikes Twice". PC Magazine. p. 206. Retrieved 25 October 2013. * ^ Callamaras, Peter V. (November 1984). "The Columbia Multipersonal Computer-VP". BYTE. p. 276. Retrieved 23 October 2013. * ^ Mace, Scott; Karen Sorensen (5 May 1986). "Amiga, Atari Ready PC Emulators". InfoWorld. p. 5. Retrieved 28 February 2011. * ^ Caruso, Denise (1984-02-27). "IBM wins disputes over PC copyrights". InfoWorld. p. 15. Retrieved 18 January 2015. * ^ Langdell, James (1984-07-10). "Phoenix Says Its BIOS May Foil IBM\'s Lawsuits". PC Magazine. p. 56. Retrieved 25 October 2013. * ^ Schmidt, Robert (July 1994). "What Is The BIOS?". Computing Basics. Archived from the original on 2012-03-10. Retrieved 2011-09-19. * ^ "Competing on Price". InfoWorld. 1985-09-30. p. 1. Retrieved 20 February 2015. * ^ Halfhill, Tom R. (December 1986). "The MS-DOS Invasion / IBM Compatibles Are Coming Home". Compute!. p. 32. Retrieved 9 November 2013. * ^ Curran, Lawrence J. (Feb 1984). "The Compatibility Craze". BYTE. p. 4. Retrieved 26 August 2015. * ^ Machrone, Bill (26 November 1985). "Compatibility Wars—Here and Abroad". PC Magazine. p. 59. Retrieved 29 October 2013. * ^ Webster, Bruce (January 1987). "View and Reviews". Byte . p. 367. Retrieved 4 November 2013. * ^ Borrell, Jerry (May 1992). "Opening Pandora\'s Box". Macworld. pp. 21–22. * ^ Parker, Rachel (1987-05-04). "PC Vendors\' Sales Rise Following PS/2 Debut". InfoWorld. pp. 1,85. * ^ A B C Scisco, Peter (December 1988). "Bus, Bus, Magic Bus". Compute!. p. 10. Retrieved 10 November 2013. * ^ LaPlante, Alice; Furger, Roberta (1989-01-23). " Compaq Vying To Become the IBM of the \'90s". InfoWorld. pp. 1, 8. Retrieved 17 March 2016. * ^ Reimer, Jeremy. "Total share: 30 years of personal computer market share figures". Ars Technica. Retrieved 13 September 2008. * ^ Miller, Michael. "Why The IBM PC Had An Open Architecture". forwardthinking dot pcmag dot com. Ziff Davis. Retrieved June 27, 2017. * ^ Brown, Marcel. "IBM Signs A Deal With The Devil". thisdayintechhistory dot com. MB Tech, Inc. Retrieved June 27, 2017. * ^ Killen, Michael (Fall 1984). "IBM Forecast / Market Dominance". Byte . pp. 30–38. Retrieved 18 March 2016. * ^ InfoWorld July 1986 ad: "Career Starter Kit: Everything you need to begin serious computing immediately". * ^ InfoWorld July 1986. * ^ Mike Tooley (2005). PC Based Instrumentation and Control (3rd ed.). Newness. p. 32. ISBN 978-1-136-37449-4 . * ^ Scott M. Mueller (2011). Upgrading and Repairing PCs (20th ed.). Que Publishing. p. 171. ISBN 978-0-13-268218-3 . * ^ Intel vs. Nvidia: The tech behind the legal case