IBM Personal Computer AT
IBM Personal System/2 | |
Related | IBM Portable PC IBM PC Convertible IBM PC XT 286 IBM RT PC |
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The IBM Personal Computer AT (model 5170, abbreviated as IBM AT or PC/AT) was released in 1984 as the fourth model in the
.Name
IBM did not specify an expanded form of AT on the machine, press releases, brochures or documentation, but some sources[3] expand the term as Advanced Technology, including at least one internal IBM document.[4]
History
IBM's 1984 introduction of the AT was seen as an unusual move for the company, which typically waited for competitors to release new products before producing its own models. At $4,000–6,000, it was only slightly more expensive than considerably slower IBM models. The announcement surprised rival executives, who admitted that matching IBM's prices would be difficult. No major competitor showed a comparable computer at COMDEX Las Vegas that year.[3]
Features
The AT is IBM PC compatible, with the most significant difference being a move to the 80286 processor from the 8088 processor of prior models. Like the IBM PC, the AT supported an optional math co-processor chip, the Intel 80287, for faster execution of floating point operations.
In addition, it introduces the
Some IRQ and DMA channels are used by the motherboard and not exposed on the expansion bus. Both dual IRQ and DMA chipsets are cascading which shares the primary pair. In addition to these chipsets, Intel 82284 Clock Driver and Ready Interface and Intel 82288 Bus Controller are to support the microprocessor.The 24-bit address bus of the 286 expands RAM capacity to 16 MB.
The motherboard includes a battery-backed real-time clock (RTC) using the Motorola MC146818.[8][9] This was an improvement from the PC, which required setting the clock manually or installing an RTC expansion card. The RTC also included a 1024 Hz timer (on IRQ 8), a much finer resolution than the 18 Hz timer on the PC.[10]
In addition to keeping the time, the RTC includes 50 bytes of
Storage
The standard floppy drive was upgraded to a 1.2 MB 5+1⁄4 inch
A 20 MB
Peripherals
The AT included the
The AT is also equipped with a physical lock that prevents access to the computer by disabling the keyboard and holding the system unit's cover in place.
ATs could be equipped with CGA, MDA, EGA, or PGA video cards.
The
Models
Power supply
The IBM PC AT came with a 192-watt
According to IBM's documentation, in order to function properly, the AT power supply needed a load of at least 7.0 amperes on the +5 V line and a minimum of 2.5 amperes on its +12 V line. The power supply would fail to start unless these minimum load requirements were met, but the AT motherboard did not provide much load on the +12 V line. To solve this problem, entry-level IBM AT models that did not have a hard drive were shipped with a 5-ohm, 50-watt resistor connected on the +12 V line of the hard disk power connector. In normal operation this resistor drew 2.4 amperes (dissipating 28.8 watts), getting fairly hot.[13]
Problems
In addition to the unreliable hard disk drive,[14] the high-density floppy disk drives turned out to be problematic. Some ATs came with one high-density (HD) disk drive and one double-density (DD) 360 KB drive. High-density floppy diskette media were compatible only with high-density drives.
There was no way for the disk drive to detect what kind of floppy disk was inserted, and the drives were not distinguished except by an asterisk molded into the 360 KB disk drive faceplate. If the user accidentally used a high-density diskette in the 360 KB drive, it would sometimes work, for a while, but the high-coercivity oxide would take a very weak magnetization from the 360 KB write heads, so reading the diskette would be problematic.
Conversely, the high-density drive's heads had a track width half that of the 360 KB drive, so they were incapable of fully erasing and overwriting tracks written by a 360 KB drive. Overwriting a DD disk that had been written in a DD drive with an HD drive would result in a disk that read on an HD drive, but produced read errors in a DD drive. Whereas a HD read head would only pick up the half track that drive had written, the wider DD read head would pick up the half-track written by the HD drive mixed with the unerased half-track remnant of the track written earlier by a DD drive. Thus, the DD drive would end up reading both new and old information together, causing it to see garbled data.
Clones
Due to[
In the United States, popular brands of AT clones included the
The AT bus became the de facto ISA (Industry Standard Architecture), while PC XT slots were retroactively named 8-bit ISA. The disk interface was standardized as ATA which evolved and was later renamed PATA (parallel ATA). Further, the same interface was originally named IDE after the fact that the drive controller was on the drive (Integrated Drive Electronics) and not on the interface card. The name IDE stuck and is more commonly known, but ATA refers to the interface specifically.
Reception
As of January 1985[update] AT sales were so strong that IBM and its suppliers could not keep up with demand.[19]
Timeline
Timeline of the IBM Personal Computer |
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Asterisk (*) denotes a model released in Japan only |
See also
References
- ^ Somerson, Paul (1984-11-13). "AT the Party". PC Magazine. p. 123. Retrieved 2014-07-05.
- ^ "IBM PC AT at Vintage Computer". Archived from the original on 2020-08-22. Retrieved 2010-10-20.
- ^ ISSN 0362-4331. Retrieved 2017-07-03.
- ^ IBM Personal System 2 and IBM Personal Computer Publication Reference Jan89 (PDF). 1989. p. 66.
- ^ "IBM PC-AT - UvA Computer Museum catalogue". University of Amsterdam. Retrieved 2023-07-15.
- ISSN 0888-8507.
- ISBN 978-81-203-3076-4.
- ISBN 978-1-4302-4972-6.
- ISBN 0-201-40996-8.
- ISBN 978-0-08-053025-3.
- ^ Dickinson, John (1985-06-25). "The AT's Slipped Disk". PC Magazine. p. 55. Retrieved 2013-10-28.
- ISBN 978-0-521-46280-8.
- ISBN 978-0-13-268218-3.
- ^ IBM's official 1986 response to "What percentage of the 20 MB drives in PC ATs have failed?" was "We consider that information to be confidential. However, based on the several customer surveys on the AT that we have conducted for IBM, an overwhelming percentage of AT owners tell us they're satisfied with the system." (questions on page 110, answers on page 111, PC Magazine, 29 April 1986). The article's opening sentence, which reads "If you own an IBM PC AT and your hard disk hasn't crashed yet, don't worry -- it probably will." Archived 2012-11-04 at the Wayback Machine was described as "a rarity in computer journalism" by the Chicago Sun-Times http://www.encyclopedia.com/doc/1P2-3760999.html and the Sun-Times called it a "badly flawed 20-megabyte" disk drive.
- ^ "HP Computer Museum". hpmuseum dot net. BGImages Australia. Retrieved 2020-07-09.
- ^ Zenith Data Systems (August 1989). "Zenith Innovates Again". PC Magazine. p. 375 – via Google Books.
- ^ "Equity II+ Product Info" (PDF). files.support.epson.com. Epson USA. Retrieved 2020-07-08.
- ^ "Equity III Product Info" (PDF). files.support.epson.com. Epson USA. Retrieved 2020-07-08.
- ^ Sanger, David E. (1985-01-18). "Computer Giant Finds Problems in Success". The New York Times. Retrieved 2011-02-25.
- ^ Ahl, David H. (December 1984). "Top 12 computers of 1984". Creative Computing. Retrieved 2019-03-16.
- ^ Jeffery, Brian (1985-09-30). "IBM's high-end micros encroaching on mini territory". Computerworld. pp. SR/20–21. Retrieved 2015-01-02.
- Notes
- IBM (1986). Personal Computer Hardware Reference Library: Guide to Operations, Personal Computer XT Model 286. IBM Part Number 68X2523.
- PC AT entry at old-computers.com
External links
- Cover story: "IBM brings out the big guns", PC Mag 13 Nov 1984, pp. 117–133
- Wiki entry for PC AT at the Vintage Computer Forums
- Historycorner.de – The IBM PC AT (IBM 5170) (in German)
- IBM 5170 information at www.minuszerodegrees.net