Sunday, August 25, 2013

In the following article we shall discuss history and evolution of microprocessors.

Introduction

The Microprocessor, also known as Central Processing Unit (CPU), is the brain of any computing device. It is an integrated chip that performs various logical and arithmetic functions on various small number holding areas called registers. Modern day microprocessor resides in our computers, phones or tablets having billion of transistors fabricated in the integrated chip and executing various programs. Here we will focus on Intel microprocessors family.

History and Evolution

History of Microprocessor started long ago in 1971, when Intel introduced first commercial microprocessor 4004 in market. The 4004 was not very powerful. it was primarily used to perform simple mathematical operations in a calculator called “Busicom.” 4004 was a 4-bit microprocessor capable of addressing 1K data memory and 4K program memory. 4004 was a Harvard architecture having 16 data registers. It could handle up to 8 inputs and 24 outputs. It had 3-level stack and operable up to 108 kHz, available in 16-pin DIP package.

Its successor was 8008 (originally called 1201), a 8-bit microprocessor with 14-bit address bus capable of addressing 16KB memory. In contrast to 4004, Intel 8008 has a von neumann architecture with only 7 data registers. It could handle up to . It had 7-level stack and operable up to 800kHz, available in 18-pin DIP package.

Next came the 8080. it was also 8-bit microprocessor,  A enhanced version of 8008. Although it is not binary code compatible with 8008, it was still source code compatible. It had many new instructions.  It could address up to 64 KB memory and handle up to 256 I/O ports. New stack pointer (SP) was introduced in 8080, which could specify the external stack in CPU memory. It was operable up to 2 MHz, available in 40-pin DIP package.

After 8080, Intel launched 8085 microprocessor. It was better than 8080 with enhancements like single 5V volt power supply, clock oscillator and system controller were on chip, serial port included in CPU, new instructions. It was operable up to 8 MHz, available in 40-pin DIP package.

Influenced by architecture of 8085, Its successor 8086, was a 16-bit microprocessor with 16-bit internal registers, 16-bit data bus, and 20-bit address bus. It was source-code compatible with 8080 and 8085. It was capable of addressing 64K 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 could be positioned anywhere in memory. So, user programs could change their position, thus memory independent code could be wrote when size of stack, data and code is less than 64KB. The complexity of the code increases when the size of stack, data and code is larger than 64 KB. This limitation is eliminated in its successor 80386 with introducing protected mode. The 8086 greatly influenced architecture of its successors, creating the base for today's highly successful x86 microprocessor family.

Feature Comparison

Microprocessor
4004
8008
8080
8085
8086
Year of introduction
1971
1972
1974
1976
1978
Clock speed
108 KHz
800 KHz
2 and 4 MHz
3, 5 and 6 MHz
5 and 10 MHz
No. of
instructions
46
66
111
113
133
No. of flags
4
4
5
5
9
Maximum memory size
4 KB (program)
640 B(data)
16 KB
64 KB
64 KB
1 MB
Add. bus width
4
8
16
16
16
Data bus width
4
8
8
8
16
IO ports
-
8 inputs
24 outputs
256 inputs
256 outputs
256 inputs
256 outputs
64K inputs
64K outputs
Technology
10 micron
10 micron
6 micron
3 micron
3 micron
No. of pins
16
18
40
40
40

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