Computer systems

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ROM

Read only memory is

memory which is non-volatile

and which contents cannot

be changed or modified. Rom is a more complex electronic circuit that does not require power to

maintain its contents. Rom contains the boot program which is used to start up the computer and load the operating system

RAM

Random access memory is a

volatile memory

that is used to temporarily

store instructions the computer is running, and the data it is processing when a computer

is running the ram will contain:

The operating system software

Application software currently being used

Any data being processed

Amount of RAM

Ram sizes can range

from 512mb to 64gb. The

more ram the more expensive it will be. Ram usually goes up in powers of

2. Buying more RAM for

your computer will increase the performance of your computer as more programs can be ran at once

Virtual memory

Virtual memory is a section of

the hard drive which is used to store information the CPU needs to process when there is

no space available in main memory. Because instructions are constantly being moved between the hard

drive, ram and CPU the performance of the computer will significantly drop.

Virtual memory is also known as secondary memory.

Cache memory

Cache memory is a very fast, very expensive

memory that is located

right next to the CPU. Cache memory is very small, a few MB, but can increase performance massively.

Cache memory is used to store data that has just been, or about to be, processed.

Flash Memory (http://www.youtube.com/watch?v=kS7gSuseE0s)

Flash memory is a type of ROM that can be re-written by applying a charge

to all or some of the circuit. Flash is used to store and boot and operating system in some

devices. Flash memory allows

the program to be updated. Flash is also used in USBs with a range from 4GB to 256GB. Access times for flash memory

are not as fast as RAM but faster than hard disks making them suitable for additional drives or back-up drives.

What is the CPU?

The CPU is the

brains of the computer where the instructions for programs and the operating system are executed, the CPU contains two parts:

Arithmetic logic unit (ALU)

Control unit (CU)

Arithmetic logic unit

The ALU is the part

of the CPU that performs calculations such as addition,

subtraction, multiplication and

comparisons such as greater than or less than

Control Unit

The CU performs the fetch-execute cycle. It

extracts instructions from the main memory, decodes them into machine code and

executes them, it sends the necessary logic signals to the ALU

Clock Speed

A vibrating crystal

alternates between a low and high voltage signal. Each low and high voltage

signal is a cycle. The

clock speed of a CPU is how many cycles it can perform per second. It is

usually measured in GHz

(billions of cycles

per second). For example a 3GHz CPU would perform 3 billion cycles per second.

Cache memory

Cache memory is a very small, very fast memory

located near the CPU to

minimise the distance instructions needs to travel along busses. Data is

taken from main memory before being stored in the cache ready to be sent to the

CPU. Cache memory is very

expensive so a mid range laptop may have 8GB RAM but only 4MB cache memory.

Cores

There is a limit to

how fast a CPU can process instructions to solve this multi-core CPUs were

invented, multi-core CPUs

are single components with two or more independent CPUs this means multiple instructions can be

executed at the same time.

Memory

CPU