GEOS SDK TechDocs
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Machine Architecture
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2 8086 Architecture Overview
The commercial microcomputer essentially began with Intel's introduction of the 8008 chip in 1972. This was an 8-bit machine that eventually led to the 8080 (in 1974), which was the precursor to the processors that now provide the power of today's PCs.
The 8080 was an 8-bit processor that used seven general-purpose registers and an external 8-bit bus. It addressed 64K of memory; such a small memory space necessitated optimization of each instruction in an attempt to keep as many instructions as possible under one byte in length. This optimization resulted in many instructions being forced to work on specific registers; for example, most arithmetic and logical operations used the accumulator as the destination register.
In 1978, the 8086 followed, bringing 16-bit architecture to microcomputers. The designers of this new chip, however, wanted to aid in quick software development, so they gave the 8086 an instruction set and architecture reminiscent of the 8080--this allowed software based on the earlier chip to be ported to the new hardware quickly and cheaply. The 8086 offered significant advances, most notably the ability to access up to one megabyte of memory in 64K segments.
A year later, in 1979, the 8088 was introduced. This chip had all the advanced features of the 16-bit 8086 except one: Rather than using a 16-bit external data bus, the 8088 used the same 8-bit bus used in the 8080. This step backwards made it possible for systems and peripherals designed for use with the 8080 to be used with a faster, more powerful chip. The 8088 was built into IBM's personal computers for just this reason.
Both the 8088 and the 8086 can run the same software; they use the same instruction set. However, the power of the data processing offered by the 8086 eventually won out as systems and software became more complex.
GEOS SDK TechDocs
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| Machine Architecture
| 2 8086 Architecture Overview