What is a computer?
• An electronic device that:
o Takes an input
o Processes data
o Delivers an output
• A computer system includes both hardware + software that work together to complete
tasks for the computer:
o Hardware = Physical things that make up the computer system (e.g. CPU,
motherboard, etc.)
o Software = Programs/applications that a computer system runs (e.g. an
operating system)
• Computers process binary data
An Introduction to Computers +
the CPU
The Purpose of the CPU (Central Processing Unit)
• The CPU is the main component of a computer
• It is known as the ‘brain’ of the computer system
• It’s main purpose it to process data + instructions
• It runs the fetch-execute (or fetch-decode-execute) cycle to do this – it fetches +
then decodes + then executes instructions
, Fetch
• 1) The memory address (e.g. 1) is copied from the PC to the MAR
• 2) The address is passed to the main memory (or RAM – Random Access Memory) to find
out the corresponding data/instructions (e.g. the corresponding instructions to address 1 is
ADD 2) – the main memory is not part of the CPU
• 3) The data/instructions (e.g. ADD 2) is passed onto the MDR
• 4) The PC is incremented by 1, ready for the next cycle
Fetc Decode
h • The data/instruction in the
MDR is then immediately
What Actions decoded by the CU to find out
The Decod what needs to be done
Occur at Each
Speed of e
Stage of the
the Cycle Fetch-Execute
Cycle
Execute
• The instruction (that has now been decoded so
The Speed of the Cycle Execu the CPU now knows what to do) is carried out
• The cycle is carried out
te • This could be:
billions of times per second
o Performing a calculation:
on a modern computer
1) The data/instructions are
• The speed depends on the
size of the computer’s passed to the ALU, which performs
processor: arithmetic + logical operations
o A 1GHz processor can 2) The result of the ALU is then
perform 1 billion temporarily stored in the ACC
3) The result can then be stored in
cycles per second
o A 3GHz processor can the main memory for later use
o Storing some data back in the main
perform 3 billion
cycles per second memory
o etc. o Halting the program
• An electronic device that:
o Takes an input
o Processes data
o Delivers an output
• A computer system includes both hardware + software that work together to complete
tasks for the computer:
o Hardware = Physical things that make up the computer system (e.g. CPU,
motherboard, etc.)
o Software = Programs/applications that a computer system runs (e.g. an
operating system)
• Computers process binary data
An Introduction to Computers +
the CPU
The Purpose of the CPU (Central Processing Unit)
• The CPU is the main component of a computer
• It is known as the ‘brain’ of the computer system
• It’s main purpose it to process data + instructions
• It runs the fetch-execute (or fetch-decode-execute) cycle to do this – it fetches +
then decodes + then executes instructions
, Fetch
• 1) The memory address (e.g. 1) is copied from the PC to the MAR
• 2) The address is passed to the main memory (or RAM – Random Access Memory) to find
out the corresponding data/instructions (e.g. the corresponding instructions to address 1 is
ADD 2) – the main memory is not part of the CPU
• 3) The data/instructions (e.g. ADD 2) is passed onto the MDR
• 4) The PC is incremented by 1, ready for the next cycle
Fetc Decode
h • The data/instruction in the
MDR is then immediately
What Actions decoded by the CU to find out
The Decod what needs to be done
Occur at Each
Speed of e
Stage of the
the Cycle Fetch-Execute
Cycle
Execute
• The instruction (that has now been decoded so
The Speed of the Cycle Execu the CPU now knows what to do) is carried out
• The cycle is carried out
te • This could be:
billions of times per second
o Performing a calculation:
on a modern computer
1) The data/instructions are
• The speed depends on the
size of the computer’s passed to the ALU, which performs
processor: arithmetic + logical operations
o A 1GHz processor can 2) The result of the ALU is then
perform 1 billion temporarily stored in the ACC
3) The result can then be stored in
cycles per second
o A 3GHz processor can the main memory for later use
o Storing some data back in the main
perform 3 billion
cycles per second memory
o etc. o Halting the program
