Microprocessors History and How They Work


All modern computers, from business servers to personal laptops to high-end gaming PCs, depend on microprocessors to function. Also known as a CPU or central processing unit, a microprocessor is a complete computation engine that has been fabricated onto a single chip.

The first microprocessor was Intel’s 4004, invented in 1971. The 4004 could only add and subtract numbers, and could only work with four bits of memory at a time, but it was an enormous technological leap. Before the 4004, engineers had to build computers from collections of chips, or discrete components of transistors wired one at a time. The first microprocessor to be used in a home computer was Intel’s 8080, an 8-bit computer chip, introduced in 1974.

Also referred to as integrated circuits, microprocessor chips are small, thin pieces of silicon onto which transistors making up the microprocessor are etched. A chip can be as large as an inch, and can contain tens of millions of transistors. A microprocessor executes a collection of machine instructions that tell a processor what to do. Based on instructions, a microprocessor can do three basic things:

  • Use its ALU (Arithmetic/Logic Unit) to perform mathematical operations like addition, subtraction, multiplication, and division. Modern microprocessors contain floating point processors that can perform sophisticated operations on floating point numbers.
  • Make decisions and jump to a new set of instructions based on those decisions.
  •  Move data from one memory location to another.

A microprocessor has:

  • An address bus (8, 16, or 32 bits wide) that sends an address to memory.
  • A data bus (8, 16, or 32 bits wide) that sends data to memory, or receives data from memory.
  • An RD (read) and WR (write) line that tells memory whether it wants to set or get the addressed location.
  •  A clock line that lets a clock pulse sequence the processor.
  • A reset line that resets the program counter to zero and restarts extraction.

Microprocessors will contain either RAM or ROM. RAM, random access memory, contains bytes of information that can be read or written, and are what allows a computer to write, save, and edit data on the fly. However, all data on RAM is lost when power is cut off, either on purpose or by accident. Therefore, ROM, Read Only Memory, is used to store critical data for the computer. ROM contains the BIOS, Basic Input/Output System. The BIOS consists of the basic instructions for the computer’s functioning, and is read by the computer during the boot-up sequence. However, ROM cannot be edited, so it cannot be used for frequently used and edited programs. 


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