The 8086 architecture, released in 1978 and introduced by Intel, was the first in the Intel X86 microprocessor family available to the public. The 8086 had a 16-bit data-bus and one megabyte (MB) of storage.
The 8086 instruction set falls in the category of Complex Instruction Set Computer (CISC). In contrast with the Reduced Instruction Set Computer (RISC), which uses multiple instructions to complete an operation, CISC computers attempt to complete operations with as few instructions as possible.
The 8086 architecture is byte addressable. In other words, each byte can be accessed with a separate address. Each word is 16 bits wide. Since a byte corresponds to eight bits, each word is two bytes wide. Data defined as 32-bit is also called "Double Word," with an address width of 20 bits. Hence, the addressable memory is two to the power of twenty bytes, which equals one MB.
The 8086 registers are divided into the following categories: General Purpose, Segment, Special Purpose and Flag.
The 8086 architecture uses the concept of segments. Each register width is 16 bits, so that's the only type it stores. The address width is 20 bits, which is generated with two registers: segment and offset. A left-shift operation is performed on the segment register. This is equivalent to multiplying the register value by 16. This shifted value is then added to the offset register to generate the memory address.
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