IBM PC 5150 64K

IBM introduced the Personal Computer (Model 5150), a minimal, open-architecture machine built from off-the-shelf parts, with a base configuration featuring 64K of RAM and no disk drive, priced at $1,379 for a single-drive system.

The IBM PC 5150 was not a clean-sheet design but a pragmatic repurposing of existing elements, most notably drawing from the IBM System/23 DataMaster, an obscure 1980 office computer⁹¹⁰. Many engineers who worked on the 5150 had previously labored on the DataMaster, and that lineage shows in the PC’s utilitarian layout and constrained expansion⁹¹⁰. The machine’s architecture centered on the Intel 8088 microprocessor, a 16-bit CPU³⁸.

Memory configuration was both a selling point and a limitation. The base model included 64K of RAM, expandable on the motherboard⁵. Full expansion to 640K was possible, though the method of expansion is not specified in the sources. A 256K RAM upgrade kit carried a list price of $360, though resellers like JADE offered it for $147.80¹. The ROM held 40Kb of firmware, including a built-in BASIC interpreter and power-on self-test (POST) diagnostics, features that eliminated the need for external boot media just to run simple programs⁸.

Storage options were strictly floppy-based. The 5150 never shipped from the factory with a hard disk, a constraint attributed to the chassis’s limited expansion room and the system’s modest resource allocation³⁴. Instead, users chose configurations with 0, 1, or 2 diskette drives with storage capacity ranging from 160Kb to 320Kb⁸. The Tandon 100-2 drive was listed at $169, while the TEAC 55B was listed at $129¹. An external 5MB hard drive, such as the one journalist Dick Pountain purchased for £1,500, was a prohibitively expensive aftermarket addition¹².

Expansion relied on five I/O slots and a socket for the Intel 8087 math coprocessor, though few users could afford both the chip and the RAM needed to exploit it²³⁴¹¹. The system also included 4-channel DMA support, a feature critical for disk and display performance⁸. The power supply delivered 63.5 watts, tight headroom that discouraged internal modifications²³⁴¹¹.

Display options split between monochrome and color. The monochrome display adapter listed for $225 ($189.95 from JADE), while the high-resolution "BoB" (Board of Boards) display adapter carried a $595 list price¹. The IBM Monochrome Display (5151001) sold for $599, despite a $275 list price, suggesting either a markup or a documentation anomaly⁶. The Color Display (5153001) was priced at $999⁶. The fact sheet provides no resolution or color depth details.

Keyboard pricing varied: the standard IBM keyboard was listed at $179, the Keytronics 5151 at $199, and a model specifically labeled "5150 keyboard" at $189⁵. Peripherals like the Microsoft Mouse retailed for $144, while the Flight Simulator package cost $34⁵. PC DOS 2.0 was sold separately for $60¹³.

By March 1983, only two official configurations remained in circulation: the Model 166 (256K RAM, one floppy) and Model 176 (256K, two floppies)²³⁴¹¹. The base 64K configuration lacked an official model number in the fact sheet, though it was offered as the "System Unit 64KB – No Drive" and "IBM CPU PC 64K 1 DRIVE"¹⁶. Motherboard variants were designated Type 1 (16/64K) and Type 2 (64/256K), with the latter supporting higher memory configurations⁷.

The 5150’s obsolescence was swift. After IBM introduced the XT on April 2, 1985, a model that included a hard drive and more expansion, the original PC became a hard sell, offering less for nearly the same price³. Its legacy lies not in longevity but in its openness: by using standard components and publishing technical details, IBM inadvertently enabled a clone market that soon eclipsed its own⁹¹⁰. The machine that began as a stopgap project in Boca Raton ended as the foundation of an ecosystem it could not control.

References

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