computer science

Página 1

The Central Processing Unit (CPU)

The CPU is the component that preforms calculations and fetches and executes program instructions.

Memory

RAM (Random Access Memory)

When a program is loaded from the computer's hard disk, its data and instructions are loaded into RAM which is normally much smaller and a lot faster than a hard disk.

When the computer is turned off or subject top a loss of power, the content of RAM is. This means Ram is volatile.

RAM is temporary storage between hard drive and CPU.

ROM ( Read Only Memory)

'Read-only' means that the content cannot be edited or deleted. As such, ROM stores data or instructions that will not need to be updated.ROM will typically store bootstrapping instructions, which tell the computer the initial steps in finding and initialising the operating system when the computer is turned on.

ROM is used to start up the computer.

Secondary memory

Main memory is volatile because it loses its content when the computer is turned off. A more long term means of storage is needed. The most common secondary storage device is a computers internal hard disk, which keeps the data and programs stored even once the computers turned off.

Optical

Is a CD,DVD and Blu-ray disks, are written to and read from using lasers. Just like magnetic disks, optical disks spin to allow the laser to read the data from the correct location. the surface of the disk will have billions of locations in which hole can be physically burned by a laser, or not burned, to represent either a 0 or a 1

Solid State

use electronic circuits, and no moving parts, to store data electronically. with no moving parts, these devices are both sturdier and quieter than magnetic or optical devices

Virtual memory

is a feature of an operating system (OS) that allows a computer to compensate for shortages of physical memory by temporarily transferring pages of data from random access memory(RAM) to disk storage.

Página 2

Networks

Is a collection of computers and other hardware that has been connected together in order to allow communication and sharing of resources.

A resource might be a file, a prio

Página 3

File Types

HTML- Hyper Text Mark-up Language Used to create websites (language of the web)

JPEG- used as image format.

BMP- used as image format.

Ping- used as image format.

MPEG- used as an animation or video format.

MP3- used as a sound format.

MP4- used as a sound format.

Gifs- used as animation format.

Input- Mice, Keyboard, Microphone, Tablet, USB, Printer

Output- Screen, Speaker, Tablet, USB, Printer

Storage:

Solid state (Expensive – used in tablets – able to move about)

Magnetic (Fairly expensive – lots of memory)

Optical (Not expensive – used for burning CDs – bad memory)

Open source: Readable available code, can be changed by everyone, unreliable (android)

Preparatory software:When bought no one can change the system, expensive, stable, and expensive (Microsoft, Apple)

Data types stored by a computer:

Date- normally in a set format

Integer- whole number

Real- decimal number

String- text

Programming:

Const VAT = 20

Input cost

Input amount sold

If sold is > 0 Total amount = Cost*

amount sold Payment = total amount*VAT/100

End if

Output payment

(Note: *= times)

DON’T PUT COMPANY NAMES e.g. IPad, kindle NO MARKSIf a system is not reliable it becomes unstable. RI-RO (rubbish in- rubbish out)

Binary

128 64 32 16 8 4 2 1

Página 4

Logic gates

Not gates

input 1 - output 0

input 0 - output 1

And gates

input 1 - input 1 - output 1

input 1 - input 0 - output 0

input 0 - input 0 - output 0

input 0 - input 1 - output 0

Or gates

input 1 - input 1 - output 1

input 0 - input 1 - output 1

input 1 - input 1 - output 1

input 0 - input 0 - output 0