- Tracing the roots of the 8086 instruction set to the Datapoint 2200 minicomputer (righto.com)
The Intel 8086 processor started the x86 architecture that is still extensively used today. The 8086 has some quirky characteristics: it is little-endian, has a parity flag, and uses explicit I/O instructions instead of just memory-mapped I/O. It has four 16-bit registers that can be split into 8-bit registers, but only one that can be used for memory indexing. Surprisingly, the reason for these characteristics and more is compatibility with a computer dating back before the creation of the microprocessor: the Datapoint 2200, a minicomputer with a processor built out of TTL chips. In this blog post, I’ll look in detail at how the Datapoint 2200 led to the architecture of Intel’s modern processors, step by step through the 8008, 8080, and 8086 processors.
- Intel 8080 (Wikipedia)
The Intel 8080 ("eighty-eighty") is the second 8-bit microprocessor designed and manufactured by Intel. It first appeared in April 1974 and is an extended and enhanced variant of the earlier 8008 design, although without binary compatibility. The initial specified clock rate or frequency limit was 2 MHz, with common instructions using 4, 5, 7, 10, or 11 cycles. As a result, the processor is able to execute several hundred thousand instructions per second. Two faster variants, the 8080A-1 (sometimes referred to as the 8080B) and 8080A-2, became available later with clock frequency limits of 3.125 MHz and 2.63 MHz respectively. The 8080 needs two support chips to function in most applications: the i8224 clock generator/driver and the i8228 bus controller. It is implemented in N-type metal–oxide–semiconductor logic (NMOS) using non-saturated enhancement mode transistors as loads thus demanding a +12 V and a −5 V voltage in addition to the main transistor–transistor logic (TTL) compatible +5 V.
