A microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip containing millions of very small components including transistors, resistors, and diodes that work together. Some microprocessors in the 20th century required several chips. Microprocessors help to do everything from controlling elevators to searching the Web. Everything a computer does is described by instructions of computer programs, and microprocessors carry out these instructions many millions of times a second. [1]
Microprocessors were invented in the 1970s for use in embedded systems. The majority are still used that way, in such things as mobile phones, cars, military weapons, and home appliances. Some microprocessors are microcontrollers, so small and inexpensive that they are used to control very simple products like flashlights and greeting cards that play music when you open them. A few especially powerful microprocessors are used in personal computers.
1. Microprocessor Evolution & Types
Intel 4004 :-
This was the first commercially available microprocessor produced in 1971.
This was a 4 bit microprocessor with 45 instructions and a speed of 50K instructions per
second (< ENIAC)
This contained 2300 PMOS transistors. It was a 4 bit device used with some other
devices to use it as a calculator.
Intel 8008 :-
In 1972, Intel designed 8008 microprocessor working with 8 bit words and Motorola
6800.
This required 20 or more additional devices to form a functional CPU.
Intel 8080 :-
Designed in 1974, 8080 had a larger instruction set and required only 2 additional
devices to form a functional CPU.
NMOS transistors were used in this for faster operations.
Intel 8085 :-
In 1977, Intel developed 8085 microprocessor with internal clock generator having
higher frequency at reduced cost and integration.
It was a single NMOS device implemented with 6200 transistors
Intel 8086 & 8088 :-
This is the first actual processor designed in 1978
Object code programs created for these processors still can be executed on the latest
members of Intel Architecture (IA) family.
8086 has 16 bit registers and 16 bit external data bus with 20-bit addressing giving 1MB
address space.
8088 was identical to 8086, except for a smaller external data bus of 8-bits.
These processors introduced IA segmentation, but only in real mode.
16-bit registers could be used as pointers to address into segments of up to 64Kbytes in
size.
Intel 80286 :-
In this processor, Protected Mode was introduced, in which segment register contents
are selectors or pointers to descriptor tables.
The descriptor provides 24 bit base addresses, allowing a maximum physical memory
size of up to 16 Mbytes, support for virtual memory management on a segment
swapping basis, and various protection mechanisms.
2. The various protection mechanisms included segement limit checking, read only and
execute only segment options, and up to four privilege levels to protect operating system
code from application or user programs.
The hardware task switching and local descriptor tables allowed the operating system to
protect application or user programs from each other.
Intel 80386 :-
This introduced 32 bit registers ( for operands) into the architecture, for both calculation
& addressing
The lower half of each 32 bit register retained the properties of one of the 16 bit registers
of the earlier two generations, to provide complete upward compatibility.
A new Virtual 8086 mode was provided to yield greater efficiency when executing
programs created for the 8086 and 8088 processors on the new 32 bit machine.
The 32 bit addressing was supported with an external 32 bit address bus giving a $
GBytes address space and also allowed each segment to be as large as 4 Gbytes.
The original instructions were enhanced with new 32 bit operand and addressing forms,
and completely new instructions were provided, including those for bit manipulation.
The Intel 386TM
processor introduced paging into Intel Architecture, with the fixed 4Kbyte
page size providing method for virtual memory management which was superior when
compared to segments.
Segmentation along with paging led to flat model addressing system in the architecture,
including complete implementations of the widely used mainframe operating system
UNIX.
Intel 80486 :-
