Unit 1 - CPU

CPU

• Central Processing Unit
• Responsible for all of the computer's processing
• Much like a human brain
• Arguabley the most important part of a computer

Control Unit

• Coordinates all the activities that take place within the CPU

ALU

• Arithmetic Logic Unit
• Responsible for all the calculations that take place in the CPU

PC

• Program Counter
• Holds the address of the next instruction that will be executed

MAR

• Memory Address Register
• Holds the memory address of current instruction
• Holds the memory address of the data that will be used

MDR

• Memory Data Register
• Holds the instruction
• Holds the data that has be fetched from the memory

Accumulator

• Holds the result of an instruction before it is transfered back to memory

Fetch

Decode

Execute

Clock Speed

• Everything in the computer acts on the impulse of an internal clock
• The faster the clock speed the faster the computer
• Because more instructions can be processed in the same time

Processor Speed

• 1 Hz = 1 instruction completed a second
• The higher the Hz the faster it is as more instructions can be completed faster
• Hz = Hertz

Multi-core processing

• The more cores a CPU has the faster it can process
• A quad core under ideal circumstances can performe four times faster than a single core
• This only really has a affect when more than one programme is being run

Cache memory

• Small amount of memory
• Really fast
• Expensive

Cache levels

• Level 1 - Extremely fast, small, located on the CPU
• Level 2 - fairly fast, medium-sized, fairly close to the processor

Benefits of Cache memory

• Data most often used is held in Level 1 and can be accessed instantly
• In most systems, 95% of the time data is accessed through level 2
• Greatly reduces time for an instruction to get from the main memory

Embedded system

• A single microprocessor
• Includes RAM, ROM and a CPU
• Used to perform only one function.
• Example - Dishwashers have Embedded systems to perform simple tasks

What is RAM

• Random Access Memory
• Can be read from
• Can be writen to
• Very fast
• Normally stores the operating system, software currently in use and data required by the software

What happens if you run out of space

• If you run ot of space on the RAM, it will go onto the virtual memory.
• This is an extension of the RAM which takes a place on the hard disk.

What is ROM

• Read Only Memory
• Stores data permenantly, even when the computer is off
• Can only be read