The Datamaster was an all-in-one computer with text-mode CRT display, keyboard, processor, memory, and two 8-inch floppy disk drives all contained in one cabinet. (Photo: Oldcomputers.net)
The Model 5150 wasn’t IBM’s first attempt at building a personal computer, with at least four previous projects being scrapped as the market moved faster than IBM’s corporate decision making. The Intel 8085-equipped System/23 DataMaster business computer also enduring a protracted development starting in February 1978. The DataMaster system entry into the market in July 1981 led to the change in design strategy in addition to members of the design team being assigned work on the new PC project.
IBM’s original plan had been to design the personal computer around Motorola’s 6800 processor at its Austin, Texas research center. IBM marketing had arranged for the PC to be sold through the stores of Sears, Roebuck & Co., and the deal teetered in the balance as Motorola’s 6800 along with its support chips slipped in schedule.
A contingency plan named Project Chess was set up to run concurrently with the Austin design and seemed to gain traction after Atari approached IBM about building a personal computer, if IBM were so inclined to design one. Official IBM sanction was achieved when project director William (Bill) Lowe pledged to have the design finalized in a year. To meet this timescale, Lowe would source from vendors outside IBM.
Project director William Lowe pledged to have the design finalized in a year sourcing components from vendors outside IBM.
What remained was choice of processor and operating system for the PC. Lowe and Estridge were astute enough to realize that IBM’s senior management would not look kindly upon a PC that posed a performance threat to the company’s lucrative business machines (a System/23 DataMaster terminal with printer listed for around $9,900 at the time).
The original intention seems to have been to use an 8-bit processor, which would have allowed MOS Tech’s 6502, Zilog’s Z80, and Intel’s 8085 to be considered. However, IBM engineers favored the use of 16-bit, as did Bill Gates, who lobbied IBM to use 16-bit to fully showcase the operating system he was developing , while the arrival of 32-bit architectures from Motorola and National Semiconductor (the 68000 and 16032 respectively) were set to enter production outside of the one year deadline.
The eventual choice was a compromise of 8-bit and 16-bit to allay concerns over compatibility with existing software and expansion options while reducing the bill of materials from a cheaper processor and support chips that were already available, and to retain a significant performance gap between the PC and IBM’s business machines.
IBM’s decision was made easier as the microprocessor landscape was becoming a war of attrition. MOS Tech was acquired by Commodore after MOS was financially decimated by Texas Instrument’s calculator price war and focus shifted from innovation to capitalizing on the success of the 6502. Western Design Center (WDC) would eventually bring 16-bit computing to the 6500 series, but as with many microprocessor companies, the competition had rendered them all redundant by the time they were ready for market.
Zilog’s fortunes also suffered a downturn, as majority shareholder and later parent company Exxon was happy to see the fledgling company go into breakneck product diversification. R&D expenditure topped 35% of revenue, while the wider range of development caused slippage in its own 16-bit Z8000 processor as Exxon’s demands and the relative managerial inexperience of Federico Faggin became exposed.
Faggin and Ungermann had started Zilog to build microprocessors, but Exxon had bought Zilog as a cog in a machine along with a host of other electronics and software company acquisitions for a grand design they hoped would rival IBM. This would turn into a billion dollar failure.
Zilog’s waning fortunes, even as its Z80 powered a prodigious number of computers, terminals, and industrial machines, also cascaded down upon its second source licensees. AMD’s license for Intel’s 8085 hadn’t translated into an invitation to do likewise with its follow up 8086 processor. For a viable 16-bit processor this left Jerry Sanders with the alternative of approaching Motorola or Zilog as National Semiconductors offering was shaping up as promising much but delivering little.
Full Story: History of the Microprocessor and the Personal Computer, Part 3 – TechSpot.