Learning objective
The processor instruction set: Understand the term ‘processor instruction set’ and know that an instruction set is processor specific. Know that instructions consist of an opcode and one or more operands (value, memory address or register). A simple model will be used in which the addressing mode will be incorporated into the bits allocated to the opcode so the latter defines both the basic machine operation and the addressing mode. Students will not be expected to define opcode, only interpret opcodes in the given context of a question. For example, 4 bits have been allocated to the opcode (3 bits for basic machine operation, eg ADD, and 1 bit for the addressing mode). 4 bits have been allocated to the operand, making the instruction, opcode + operand, 8 bits in length. In this example, 16 different opcodes are possible (24 = 16).
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Structure and role of the processor and its components
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The processor instruction set
Aqa A Level Computer ScienceFundamentals of computer organisation and
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Quick explanation
The processor instruction set: Understand the term ‘processor instruction set’ and know that an instruction set is processor specific. Know that instructions consist of an opcode and one or more operands (value, memory address or register). A simple model will be used in which the addressing mode will be incorporated into the bits allocated to the opcode so the latter defines both the basic machine operation and the addressing mode. Students will not be expected to define opcode, only interpret opcodes in the given context of a question. For example, 4 bits have been allocated to the opcode (3 bits for basic machine operation, eg ADD, and 1 bit for the addressing mode). 4 bits have been allocated to the operand, making the instruction, opcode + operand, 8 bits in length. In this example, 16 different opcodes are possible (24 = 16)
- This point belongs to Structure and role of the processor and its components, especially The processor instruction set.
- You need to be able to the processor instruction set: Understand the term ‘processor instruction set’ and know that an instruction set is processor specific. Know that instructions consist of an opcode and one or more operands (value, memory address or register). A simple model will be used in which the addressing mode will be incorporated into the bits allocated to the opcode so the latter defines both the basic machine operation and the addressing mode. Students will not be expected to define opcode, only interpret opcodes in the given context of a question. For example, 4 bits have been allocated to the opcode (3 bits for basic machine operation, eg ADD, and 1 bit for the addressing mode). 4 bits have been allocated to the operand, making the instruction, opcode + operand, 8 bits in length. In this example, 16 different opcodes are possible (24 = 16).
- Use the linked flashcards and practice questions to check recall, then practise applying the idea in an exam-style answer.
Why it matters
This objective helps connect The processor instruction set to exam-style questions, flashcards, and revision notes for Structure and role of the processor and its components.
Quick student answer
What is meant by a processor instruction set?
Direct answer
The collection of instructions that a processor can interpret and execute
Key terms
- Processor instruction set: The set of instructions that a particular processor can interpret and execute.
- Operand: The part of an instruction that provides a value, memory address or register for the operation.
Common trap
Treating the operand as the operation: The opcode identifies the basic machine operation and, in this model, the addressing mode. The operand supplies a value, memory address or register.
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Related learning objectives
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