Microprocessor Overview 8086 - Microprocessor

Discuss the overview of Microprocessor 8086?

As we have discussed about 8085 Microprocessor in earlier sessions, this 8086 Microprocessor is an enhanced version of 8085Microprocessor that was designed by Intel in between 1976-1978. It is a 16-bit Microprocessor used as CPU in a Microprocessor possessing 20 address lines and16 data lines that supports up to 1MB storage. It accepts instructions in the form of 16-bit binary words. It possesses powerful instruction set, which helps in performing certain operations like multiplication and division easily.
It supports two hardware modes of operation, i.e. Maximum mode and Minimum mode. Maximum mode is suitable for large application system having multiple processors and Minimum mode is suitable for system having a single processor as all the control signals are given out by the microprocessor chip only.

Features of 8086

The most prominent features of a 8086 microprocessor are as follows −
  • It has a powerful instruction queue, which helps in storing of six instruction bytes from the memory. This indicates in faster processing.
  • It was the first 16-bit processor having 16-bit ALU, 16-bit registers, internal data bus, and 16-bit external data bus resulting in faster processing.
  • It is available in 3 versions based on the frequency of operation −
    • o8086 → 5MHz
    • o8086-2 → 8MHz
    • o(c)8086-1 → 10 MHz
  • It uses two stages of pipelining, i.e. Fetch Stage and Execute Stage, which improves performance.
  • Fetch stage can pre fetch up to 6 bytes of instructions and stores them in the queue.
  • Execute stage executes these stored instructions.
  • It has 256 vectored interrupts.
  • It consists of 29,000 transistors.

Comparison between 8085 & 8086 Microprocessor

  • Size − 8085 is 8-bit microprocessor, whereas 8086 is 16-bit microprocessor.
  • Address Bus − 8085 has 16-bit address bus while 8086 has 20-bit address bus.
  • Memory − 8085 can access up to 64Kb, whereas 8086 can access up to 1 Mb of memory.
  • Instruction − 8085 doesn’t have an instruction queue, whereas 8086 has an instruction queue.
  • Pipelining − 8085 doesn’t support a pipelined architecture while 8086 supports a pipelined architecture.
  • I/O − 8085 can address 2^8 = 256 I/O's, whereas 8086 can access 2^16 = 65,536 I/O's.
  • Cost − The cost of 8085 is low whereas that of 8086 is high.

Architecture of 8086

The following diagram depicts the architecture of a 8086 Microprocessor −

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