Computer Hardware

Main Parts of a Computer:

• CPU (Central Processing Unit) or Microprocessor
• Random Access Memory – RAM
• Read-only memory – ROM
• Basic Input/output system – BIOS
• Motherboard
• Hard Disk or secondary memory
• Various Input/Output devices

What happens when you turn a computer on?

1. BIOS runs – it checks memory and for the existence of I/O devices
2. BIOS loads in the operating system (Windows 2000)
3. Operating system lets you run programs and sends output to correct devices.

What does a microprocessor do?

1. Simple math (add, subtract, multiply and divide
2. Movement of data from one memory location to another
3. Comparisons of values (<, >, =)
4. Movement from one set of instructions to another

It contains:

• Busses – wires that move data between the CPU and memory
• Registers – temporary data locations within the CPU
• ALU – logic circuitry that performs the math and comparisons
• Control Unit – logic that moves data in and out of the CPU

Performance is measured by speed:

1.5 gigahertz (clock speed) in a Pentium 4

1.7 billion instructions per second

How does memory work?

• Random Access Memory (DRAM) is a capacitor which needs to be recharged. If charge level is high, it is a “1”. If it is low, it is a “0”.
• “Refreshing” is necessary to keep bringing capacitors up to charge. If refreshing stops (like when you turn the computer off), all memory goes to 0.

• Secondary memory is kept more permanently either by magnetizing pieces of plastic (your floppy disk) or marking up an optical disk (CD)

• Memory is measured in bytes – the memory needed to store one letter of the alphabet. Good computers will have at least 64 million (mega) bytes RAM, and 5-10 billion (giga) bytes of hard disk storage