Yesterday & Today
At the heart of the microprocessor-based
computer system is the microprocessor integrated circuit. The microprocessor is the
controlling element in a computer system and is sometimes referred to as the CPU (central
Processing Unit). The microprocessor controls memory and I/O through a series of
connections called buses. Buses select an I/O or memory device, transfer data between an
I/O device or memory and the microprocessor, and control the I/O and memory system. Memory
and I/O are controlled through instructions that are stored in the memory and executed by
the microprocessor. The power of microprocessor is in its ability to execute millions of
instructions per second from a program or software stored in the memory system.
The microprocessor performs three main tasks for the computer system.
The worlds first microprocessor, the Intel 4004, was a 4-bit microprocessor- a programmable controller on a chip. It addresses a mere 4,096 4-bit wide memory locations. A bit is a binary digit with a value of one or zero. A 4-bit wide memory location is often called a nibble. A 4-bit microprocessor debuted in early video game systems and small microprocessor based control systems. Most calculators are also still based on 4-bit microprocessor that process 4-bit BCD(binary-coded decimal) codes. In 1971, Intel Corporation released the 8088-an extended 8-bit version of the 4004 microprocessor.
In 1978, Intel released the 8086 microprocessor. It was 16-bit microprocessor, which executed instructions in as little as 400 ns (2.5 MIPs or 2.5 million instruction per second). 8088 and 8086 addressed 1M byte system. In 1983 Intel introduced 80286 microprocessor. 80286 microprocessor was identical to the previous microprocessor, except it addressed a 16M byte memory system.
In 1986, 80386 microprocessor was introduced. The 80386 was Intels first 32-bit microprocessor that contained a 32-bit data bus and a 32-bit memory addresses. Again in 1989, Intel released the 80486 microprocessor. The internal structure of 80486 was modified, so half of its instructions is executed in one clock instead of two clocks.
The Pentium, introduced in 1993, was similar to the 80386 and 80486 microprocessor. It was labeled as P5 or 80586. Pentium operated with a clocking frequency of 60 Mhz and 66 Mhz and a speed of 110 MIPs, with a higher frequency of 100 Mhz one and one-half clocked version operating at 150 MIPs. In 1995, Intel introduced Pentium Pro microprocessor. They contains 21 million transistors, 3 integer units, as well as a floating-point unit to increase the performance of most software. The basic clock frequency is 150 Mhz, 166 Mhz , 200 Mhz, 233 Mhz. Pentium Pro can address either a 4G byte memory system or a 64G byte memory system.