Exam Board:
Cambridge OCR
1.1a: The CPU
Specification:
GCSE - J277
Watch on YouTube:
The CPU
The function of each CPU component:
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Control Unit (CU)
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Arithmetic Logic Unit (ALU)
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Registers
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Cache
What Von Neumann architecture is.
What You Need to Know
The Central Processing Unit
The Central Processing Unit (CPU) is the most important component in any computer system.
Like many computer components, it is attached to the motherboard.
The purpose of the CPU is to process data and instructions by constantly repeating the fetch-execute cycle.
CPU Components
The Control Unit (CU) sends signals to control hardware and coordinate the flow of data inside the CPU and across the computer.
It also decodes instructions as part of the fetch-execute cycle.
The Arithmetic Logic Unit (ALU) performs mathematical calculations, logical operations and binary shifts.
The results of calculations made by the ALU are stored in a register called the accumulator.
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A register is a temporary storage space for one piece of data, instruction or address.
Different registers are used during the fetch-execute cycle.
Cache memory stores frequently accessed data and instructions because it is much faster for the CPU to access (fetch from) than RAM.
Computer Architecture
The way a computer is designed and structured is known as its architecture.
A common type of computer architecture is Von Neumann (pronounced Von Noy-man), named after mathematician John Von Neumann.
Von Neumann Architecture
Instruction
Data
RAM
ADD
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A computer with Von Neumann architecture stores both program instructions and data in the same memory (RAM). This is different from other architectures that have an instruction memory and a separate data memory.
Instructions (technically called the opcode) and data (technically called the operand) are not the same.
An instruction is an action to perform and data is the value to be used. For example with the command 'ADD 43', ADD is the instruction and 43 is the data.
Von Neumann architecture also contains the key CPU components of a control unit, arithmetic logic unit (ALU), registers and cache memory.
Questo's Questions
1.1a - The CPU:
1a. What does 'CPU' stand for? [1]
1b. What is the purpose of the CPU? [2]
2. Draw a diagram of the CPU, and label the four main components. [4]
3. Describe the purpose of:
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a. The Control Unit [2]
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b. The ALU [2]
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c. The registers [2]
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d. Cache memory [2]
4a. Describe the key feature of Von Neumann architecture. [2]
4b. Explain how an instruction is different to data. [2]