Gregory's ServerThe Datamaster, also known as the IBM System/23, was released in July 1981, just a month before the IBM PC. The 16-bit PC overshadowed the 8-bit Datamaster as it was both more powerful and cheaper. But the Datamaster is interesting since it is the IBM PC's parent. 2/8
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 The Datamaster had an 80×24 display, matching IBM's popular 3270 terminal. (80 columns date back to punch cards.) The IBM PC was going to copy the Datamaster's display, but they managed to squeeze in one more line. That's why today's console windows default to 80×25. 4/8 The Datamaster in my photos is at the System Source computer museum in Hunt Valley MD, just outside Baltimore. The museum is well worth a visit if you're in the area. 5/8 Getting back to the 8088's system bus, the bus uses a four-step sequence of operations to access memory or I/O devices. These steps are called T-states: T1, T2, T3, and T4. A read operation provides the address during T1 and receives the data during T3. 6/8 A complicated state machine moves the processor through the T-states. This diagram shows the location of the bus state machine circuitry on the die of the 8088 processor. Back in 1979, just a few flip-flops and logic gates occupied a substantial area on the die. 7/8 The 8088's bus state machine is too complicated to explain here. Instead, see my blog post for lots of diagrams and schematics: https://www.righto.com/2024/04/intel-8088-bus-state-machine.html 8/8  @kenshirriff If anything that also shows just how optimized the rest is to not fit all the functionality in the rest of the space, especially with the decode logic taking up so much too. |
The Datamaster influenced the PC in many ways. Both desktop computers used BASIC. The PC used the same keyboard, but detached from the unit. The PC's 62-pin expansion bus came from the Datamaster. 3/8