OCR J277/01 – 1.2 Memory and Storage

The need for primary storage
The difference between RAM and ROM
The purpose of ROM in a computer system
The purpose of RAM in a computer system
Virtual memory

The need for secondary storage
Common types of storage:

Optical
Magnetic
Solid state

Suitable storage devices and storage media for a given application
The advantages and disadvantages of different storage devices and storage media relating to these characteristics:

Capacity
Speed
Portability
Durability
Reliability
Cost

The units of data storage:

Bit
Nibble (4 bits)
Byte (8 bits)
Kilobyte (1,000 bytes or 1 KB)
Megabyte (1,000 KB)
Gigabyte (1,000 MB)
Terabyte (1,000 GB)
Petabyte (1,000 TB)

How data needs to be converted into a binary format to be processed by a computer
Data capacity and calculation of data capacity requirements

Numbers
How to convert positive denary whole numbers to binary numbers (up to and including 8 bits) and vice versa
How to add two binary integers together (up to and including 8 bits) and explain overflow errors which may occur
How to convert positive denary whole numbers into 2-digit hexadecimal numbers and vice versa
How to convert binary integers to their hexadecimal equivalents and vice versa
Binary shifts

Characters
The use of binary codes to represent characters
The term ‘character set’
The relationship between the number of bits per character in a character set, and the number of characters which can be represented, e.g.:

ASCII
Unicode

Images
How an image is represented as a series of pixels, represented in binary
Metadata
The effect of colour depth and resolution on:

The quality of the image
The size of an image file

Sound
How sound can be sampled and stored in digital form
The effect of sample rate, duration and bit depth on:

The playback quality
The size of a sound file

The need for compression
Types of compression:

Lossy
Lossless