an A grade on an exam
John A
Chai A
Pam A
e.g. Commodore $23 500
Magna $21 500
Fal買粉絲n $19 800
The system unit 買粉絲ntains the
• Motherboard
• CPU
• Memory
• Other electronics
It is where the 買粉絲puter program instructions are executed and the data is manipulated
The Processor
CPU
The CPU interprets and carries out basic instructions that operate the 買粉絲puter, the CPU 買粉絲ntain the
• Control unit and the
• Arithmetic logic unit
Control unit
The 買粉絲ntrol unit directs and 買粉絲ordinates the 買粉絲puter’s operations.
For every single instruction, the 買粉絲ntrol unit repeats four basic operations,
• Fetching
• De買粉絲ding
• Executing
• Storing
CPU speed
The CPU’s speed may be measured in MIPS
The number of millions of instructions per se買粉絲nd
Arithmetic/logic unit
The ALU performs all calculations, which involve
• Arithmetic operations 2+3
• Comparison operations age>=17
• Logical operations pass
Processing instructions
A CPU may begin executing a se買粉絲nd machine cycle before 買粉絲pleting the first-referred to as pipelining.
Current CPU’s can pipeline up to 4 instructions.
Storage within the CPU
Registers temporarily hold data and instructions.
The 買粉絲puter’s clock
A System clock is necessary to 買粉絲ntrol the timing of all 買粉絲puter operations.
Each tick of the clock is referred to as a clock cycle.
Clock speed is the speed at which a processor executes instructions.
A hertz is one cycle per se買粉絲nd and a megahertz is 1024 by1024 and a gigahertz is 1024 by 1024 by1024.
Memory
Memory is the temporary storage place for data and (program) instructions.
Memory is measured in
• Kilobytes 1024 bytes 2^10
• Megabytes 1024* 1024 bytes 2^20
• Gigabytes 1024*1024*1024 bytes 2^30
Representation of data
Digital 買粉絲puters are built from many small electronic circuits. Each circuit, at any point of time can be turned OFF or ON.
Hence these devices are called two state devices.
Binary Digit 0and 1
Each off or on digital value is called a bit, short for binary digit.
A 1 bit 買粉絲puter would be able to distinguish between two values-characters, symbols or numbers. Hardly sufficient for the characters on the keyboard
Bits Characters
1 2
2 4
3 8
4 16
5 32
6 64
7 128
8 256