1. Motherboard External Hard disk USB 1 DVD Drive RAM CPU (Main Memory)
CPU speed or clock speed is measured in Hz (cycles per second)
A mid range laptop my have clock speed of 3GHz (3 billion cycles per second/300 million instructions per second)
Very fast access time, almost as fast as the CPU
Measured in Mb (2- 3Mb in a typical laptop)
££££
Can read ahead to store other instructions that are likely to be used next
Stores programs (instructions) and data when NOT in use (non volatile)
Relatively slow access time
Measured in Tb
Stores programs (instructions) and data when in use (volatile)
Fast access time but not as fast as the CPU can process instructions
Measured in Gb (Typical laptop may have 4-6Gb of RAM)
£££
External Hard disk
USB 1
Motherboard
ALU
CPU CU
DVD Drive
Cache memory
RAM
(Main Memory)
Hard disk
ROM
Data is moved around on ‘buses’ (measured in MHz)

2. Multi Core Processor – Principles are the same but the number of processors are increased
Motherboard
ALU
CPU CU
Cache memory
ALU
CPU CU
Cache memory
RAM
(Main Memory)
Hard disk
ROM

3. Factors affecting CPU speed
Clock speed
Cache size
Bus Speed
Number of processor cores
Word size – (The number of bits the CPU can process in one go – typically 32 or 64 bits)

4. Motherboard External Hard disk USB 1 DVD Drive RAM CPU (Main Memory)
Very fast access time, almost as fast as the CPU
Measured in Mb (2- 3Mb in a typical laptop)
££££
Can read ahead to store other instructions that are likely to be used next
Static RAM
4/5 transistors per bit. Do not need to be refreshed.
Fast yet expensive
Secondary Storage
Stores programs (instructions) and data when NOT in use (non volatile)
Relatively slow access time compared to RAM
Measured in Tb
Stores programs (instructions) and data when in use (volatile)
Fast access time but not as fast as the CPU can process instructions
Measured in Gb (Typical laptop may have 4-6Gb of RAM)
£££
Dynamic RAM
One transistor and one capacitor per bit.
Needs constantly ‘refreshed’
Flash Memory – A type of ROM that is ‘writeable’. Involves using a large ‘flash’ of electrical current to trap electrons.
Slow compared to RAM but fast compared to magnetic/optical technologies.
External Hard disk
USB 1
Motherboard
ALU
CPU CU
DVD Drive
Cache memory
RAM
(Main Memory)
Hard disk
Virtual Memory – Used when RAM is full
ROM
Data is moved around on ‘buses’ (measured in MHz)
ROM – Read Only Memory. Similar to RAM but cannot be written to and is Non Volatile. Used to store ‘boot’ sequence. PROM/EPROM/EEPROM