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Thursday, November 23, 2017

What "bit" architecture did the Intel 8086 use?

What "bit" architecture did the Intel 8086 use?

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What "bit" architecture did the Intel 8086 use?


Intel 8086 microprocessor is a first member of x86 family of processors. Advertised as a "source-code compatible" with Intel 8080 and the Intel 8085 processors, the 8086 was not object code compatible with them. The 8086 has complete 16-bit architecture - 16-bit internal registers, 16-bit data bus, and 20-bit address bus (1 MB of physical memory). Because the processor has 16-bit index registers and memory pointers, it can effectively address only 64 KB of memory. To address memory beyond 64 KB the CPU uses segment registers - these registers specify memory locations for code, stack, data and extra data 64 KB segments. The segments can be positioned anywhere in memory, and, if necessary, user programs can change their position. This addressing method has one big advantage - it is very easy to write memory-independent code when the size of code, stack and data is smaller than 64 KB each. The complexity of the code and programming increases, sometimes significantly, when the size of stack, data and/code is larger than 64 KB. To support different variations of this awkward memory addressing scheme many 8086 compilers included 6 different memory models: tiny, small, compact, medium, large and huge. 64 KB direct addressing limitation was eliminated with the introduction of the 32-bit protected mode in intel 80386 Processor


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