1. AS Level ICT
Selection and use of storage requirements, media, and devices: storage and storage capacity
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

2. Primary and Secondary storage
The two means of storing programs and data in a computer system are:
Primary storage – this is storage that uses chips within the control, arithmetic, and logic units
Secondary storage – also know as backup storage, this uses media that is outside the control, arithmetic, and logic units
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

3. Primary storage The two types of primary storage chips are:
ROM – Read Only Memory
RAM – Random Access Memory
The programs and data stored on these ROM and RAM chips are available as soon as the computer is switched on
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

4. ROM
ROM is fast, permanent memory used for holding the instructions that are needed to start a computer
It is stored on a memory chip inside the combined control, arithmetic, and logic units
It is non-volatile memory because it is not lost when the power is turned off
The contents of ROM cannot be altered by the user
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

5. RAM
ROM is fast, temporary memory used for holding any programs and data that are being used at a particular time
It is stored on a memory chip inside the combined control, arithmetic, and logic units
It is volatile memory because it is lost when the power is turned off
The contents of RAM is read/write memory and can be altered by the user
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

6. Memory size As with most things in life, size does matter!
The larger the memory available …
The faster applications will run
The larger the number of applications that can be run at the same time
The quicker it is for the user to switch from one application to another
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

7. Measuring memory Memory is measured using a binary-based system
A single character typed on a keyboard will take up one byte (one byte is made up of 8 bits [binary digits] and is 2 x 2 x 2 bits)
The byte is the smallest unit of measure usually used when describing the size of memory
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

8. Measuring memory
1024 bytes are called a kilobyte (approximately 1000 bytes): abbreviation = Kb
1024 kilobytes are called a megabyte (approximately 1000 kilobytes): abbreviation = Mb
1024 megabytes are called a Gigabyte (approximately 1000 megabytes): abbreviation = Gb
1024 gigabytes are called a Terabyte (approximately 1000 gigabytes): abbreviation = Tb
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

9. Measuring storage capacity and performance
Storage capacity is usually measured in Mb or Gb, although it is likely that Tb will be used more and more in the future, and Mb will become as little used as Kb has
The terms commonly used to describe storage are:
Storage density – how much space does the storage medium take up? (N.B. the smaller the storage medium for a given storage capacity, the better!)
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

10. Measuring storage capacity and performance
Access time – How long does it take for a particular piece of data to be accessed from or saved to the storage device? (N.B. The quicker, the better!)
Transfer rate – What is the throughput of the transfer of data to and from the storage device? (N.B. the more data that can be transferred in a given time, the better!)
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

11. Measuring storage capacity and performance
Physical size – storage devices need to be as light and as small as possible
Portability – some storage devices, particularly those used as backups, are removable so that they can be stored in a safe and secure area away for the computer; it is therefore important that they are as portable as possible
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity

12. AS Level ICT
Selection and use of storage requirements, media, and devices: storage and storage capacity
Unit 1 Topic a - Selection and use of storage requirements, media, and devices: Storage and storage capacity