Exam Board:
OCR
1.1a: The CPU
Specification:
J277
Watch on YouTube:
Purpose of the CPU
CPU Components
Von Neumann Architecture
The Central Processing Unit (CPU) is the most important component in any computer system.
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Like many computer components, it is attached to the motherboard.
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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 control signals to direct the operation of the CPU.
Control signals and timing signals are sent to the ALU and other components such as RAM.
It also decodes instructions as part of the fetch-execute cycle.
ALU stands for ‘Arithmetic and Logic Unit’.
It performs simple calculations and logical operations.
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A register is a temporary storage space for one instruction or address.
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Different registers are used during the fetch-execute cycle.
Cache memory is used to temporarily store data that is frequently accessed.
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Cache memory is split into different levels.
Cache is slower to access than the registers but much faster than RAM.
Computer Architecture
The way a computer is designed and structured is known as its architecture.
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The most common type of computer architecture is Von Neumann. It is named after the mathematician John Von Neumann (pronounced Von Noy-man)
Von Neumann Architecture
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​A computer with Von Neumann architecture stores both program instructions and data in the same memory (RAM) and in the same format (in binary).
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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.
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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:
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1a. What does 'CPU' stand for? [1]
1b. What is the purpose of the CPU? [2]
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2. Draw a diagram of the CPU, and label the four main components. [4]
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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]
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4a. Describe the key feature of Von Neumann architecture. [2]
4b. Explain how an instruction is different to data. [2]