IBM Personal Computer

The IBM Personal Computer, usually recognized as the IBM PC, is the innovative adaptation and progenitor of the IBM PC attuned hardware platform. It is IBM model number 5150 that was introduced on August 12, 1981. It was shaped by a group of engineers and designers under the trend of Don Estridge of the IBM Entry Systems Division in Boca Raton, Florida.

The phrase "personal computer" was already common in usage before 1981, and was used in the early days of 1972 to distinguish Xerox PARC's Alto. Nevertheless, because of the success of the IBM PC, what had been a standard term became to often particularly signify a microcomputer attuned with IBM's PC products.

Idea of IBM

The first PC was an IBM effort to penetrate into the small computer market then monopolized by the Commodore PET, Atari 8-bit family, Apple II and Tandy Corporation's TRS-80s, and various machines. IBM's first desktop microcomputer was the IBM 5100 launched in 1975, but its cost was sky scraping in contrast to microprocessor based machines.

Adapting a non traditional approach, an unusual group was gathered with approval to avoid normal company limits and get something to market fast. This project was given the code name Project Chess.

The team had twelve people lead by Don Estridge and Chief Scientist Larry Potter. They made the PC in about a year. To get this they initially determined to structure the machine with off-the-shelf parts from a assortment of diverse unique equipment manufacturers (OEMs) and countries. Formerly IBM had produced their own gears. Eventually, they decided on an open structural design so that other producers could design and sell secondary machinery and compatible software. IBM also sold an IBM PC Technical Reference Manual which incorporated a list of the ROM BIOS source code.

The original PC had a edition of Microsoft BASIC —IBM Cassette BASIC— in ROM. The CGA (Color Graphics Adapter) video card could use a typical television set or an RGBI monitor for display; IBM's RGBI monitor was the display model 5153. The other option that offered by IBM was an MDA (Monochrome Display Adapter) and the monochrome display unit 5151. It was promising to install both an MDA and a CGA card and use both display units at the same time, if supported by the program being executed. Such as, AutoCAD allowed use of a CGA card for graphics and a separate monochrome board for text menus. A few model 5150 PCs with CGA monitors and a copier port also incorporated the MDA adapter by default, since IBM provided the printer port and MDA port on the same adapter card; it was in reality an MDA/printer port combo card.

The most frequently used storage medium was the floppy disk, though cassette tape was initially predicted by IBM as a low funded substitute. As a result, the IBM 5150 PC was accessible with one or two floppy drives or with no drives or storage media; in the latter case IBM planned that users attach their own existing cassette recorders via the 5150's cassette jack. A hard disk could not be put into the 5150's system unit without reinforcing a stronger power supply, but an "Expansion Unit", also referred as the "IBM 5161 Expansion Chassis" was obtainable, which came with one 10MB hard disk and also permitted the setting up of a second hard disk. The system unit had five extension slots; the extension unit had eight; though, one of the system unit's slots and one of the expansion unit's slots had to be occupied by the Extender Card and Receiver Card, respectively, which were needed to attach the expansion unit to the main system unit and make the expansion unit's other slots on hand, for a total of 11 slots, a
few of which though had to already be engaged by display, disk, and I/O adapters, etc. as none of these were existing on-board with the 5150; the only on-board connectors were the keyboard and cassette ports. The original PC's maximum memory using IBM parts was 256 kB, 64 kB on the main board and three 64 kB extension cards. The processor was an Intel 8088 (early on 1978 version, later were 1978/81/82 versions of Intel chip; second-sourced AMDs were used after 1983) operating at 4.77 MHz (4/3 the typical NTSC color burst frequency of 3.579545 MHz), which could be substituted with a NEC V20 for a minor boost in processing speed. An Intel 8087 co-processor could also be added for hardware floating-point arithmetic. IBM sold it in configurations with 16 kB or 64 kB of RAM pre incorporated using either nine or thirty-six 16-kbit DRAM chips.

Even though the TV-compatible video board, cassette port and FCC Class B guarantee were all intended at turning it into a home computer the original PC proved too costly for the domestic market. At the beginning a PC with 64 kB of RAM and a single 5 1/4 inch floppy drive and monitor sold for US $3,005, while the cheapest configuration ($1,565) that had no floppy drives, only 16KB RAM, and no display units were too unappealing. While the 5150 did not turned to be a top selling home computer, its floppy-based design became a surprisingly big hit with businesses.