Computer Science theory IGCSE

3 secondary storage devices

1. Magnetic Disks

2. Optical Storage

3. Solid State Drives

What shape is on Magnetic Disks

Concentric circles (tracks) which are divided into sections

What is the advantages of Magnetic Disks

1. Cheap

2. Large Capacity

3. Fast write speed

What are the drawbacks of Magnetic Disks

1. Lots of mechanical parts

2. Bad Durability

3. Not very portable

How much storage is on a magnetic disk

500GB - 12TB or more

How is optical storage stored

Data is stored in spiral tracks (laser reflects of the pits = 0)

3 examples of optical storage

1. CD-ROM

2. DVD

3. Blu-Ray

2 Advantages of optical storage

1. Cheap

2. Portable

3. Takes up little space

2 Disadvantages of optical storage

1. Less storage

2. Not very durable

3. A reader is required

4. Slow write speed

Uses of optical storage

1. Songs

2. Videos

3. Backup

4. Multi media

2 Advantages of Solid State Drives (SSD)

1. Very durable

2. No moving parts

3. Fast write speeds

4. Fast start ups

2 disadvantages of SSD’s

1. More expensive

2. Similar storage to Magnetic Disks

Capacity of SSD’s

100GB - 16TB

How do SSD’s store information

They use non-volatile flash memory to store information

Purpose of the CPU

1. Run instructions for programs/algorithms

2. Controls computer parts

Where are all devices in a computer located

Motherboard connecting them to the CPU

Where are instructions fetched from

RAM or CPU (one at a time)

3 components in the CPU

1. ALU - arithmetic logic unit

2. CU - control unit

3. Registers

What are registers

Small blocks of volatile memory that store temporary values (used as instructions for CPU)

How fast are registers

As fast as the CPU

What are registers with specific purposes called

Special purpose registers

What does the ALU do

1. Responsible for manipulating numbers with calculations (e.g. +,-,x)

2. Logical operations

What does the ALU use

Special purpose register called Accumulator (ACC)

Stores results of calculation or operation

What does the CU do

1. Manages Decoding instructions

2. Manages execution of instructions

3. Sends and receives control signals

4. Sends regular pulse to CPU to control timing

What is a bus

Set of parallel wires connecting two or more components

Name 3 buses

1. Address bus - carries address of memory or device to be read

2. Data bus - carries data to and from CPU

3. Control bus - carries control signals to control all activities in CPU

When is the address bus needed

When the CPU wishes to access a particular main memory location

How many devices can use a bus at a time

1

What 3 operations does the CPU repeat

1. Fetch - from main memory

2. Decode - work out what is being asked

3. Execute - instruction is run

Where is a program loaded when executed

Storage to RAM

What does the address bus do

Carries memory address pointing to the location of the first instruction inside RAM

Which bus is unidirectional

Address bus

What is faster single or dual core

Dual core

What is clock speed

Number of (Fetch, decode, execute) cycles it can do in a second

What is clock speed measured in

Hertz (Hz)

Why does RAM have a clock speed

It is the time taken for it to fetch one item of data

What is Cache memory

Stores the frequently accessed data/instructions

Is faster than RAM

How does Cache memory benefit the CPU

Because it’s fast instructions can be fetched faster so the CPU is not idle

(It is expensive)

Factors affecting CPU performance

1. Number of cores

2. Cache size

3. Clock speed

What is RAM

Random access memory - can be added to and be read (contents change)

Temporary storage data is volatile

What is faster RAM or a storage device

RAM

What is ROM

Read Only Memory - stores startup instructions and stores Basic Input Output System (BIOS) and is non-volatile

2 things boot software on ROM does

1. Does self test

2. Boots OS

3. Checks if RAM is connected

4. Checks if there are connected devices

2 types of inputs

1. Keystrokes

2. Mouse clicks

3. Sensors

2 examples of outputs

1. Reports

2. Notifications

3. Displays

Pixel definition

Smallest element of a bitmap image

What is image resolution

Density of pixels in a image

How to calculate color depth

2 to the power of the number of bits

What happens if a image resolution increases

Better image quality, takes up more storage

How do you calculate file size

Width X hight X color depth (%8 to get Bytes and then %1000 to get KB)

How to get from a MG to a GB

X1000

3 examples of metadata

1. File type

2. Height

3. Width

4. Color depth

5. Resolution

6. Time/date edited

Analogue definition

Constantly changing

What is bit depth

Number of bits used to record each sample

What is sample interval

The length of time between each sample

What happens if the sample rate is high

Level of detail in the sound will increase being more accurate

What is sample rate

Number of samples per second

How to calculate file size of a image

Sample rate X bit depth X duration