Computer Architectures (Cambridge International A-Level Computer Science)
Exam board Cambridge International · A-LevelUpdated 2025-05-14
Architecture types
What is a computer architecture?
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A computer architecture is the design and structure of a computer system
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It describes how it fetches, processes, and stores data and instructions
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It defines how components like the CPU, memory, and input/output devices work together to execute programs
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Each architecture is categorised as:
- Single or Multiple Instruction stream
- Single or Multiple Data stream
SISD – Single Instruction, Single Data
| Description | Key Features |
|---|---|
| One processor executes one instruction on one data stream at a time | Traditional serial (non-parallel) architecture |
| Used in basic, single-core processors | Step-by-step processing |
Example: Classic desktop CPU running one task at a time
Single Instruction, Single Data Diagram
SIMD – Single Instruction, Multiple Data
| Description | Key Features |
|---|---|
| One instruction is applied to multiple pieces of data at once | Useful for parallel processing |
| All processing units perform the same operation in parallel | Ideal for graphics or scientific computation |
Example: GPU operations, image processing
Single Instruction, Multiple Data Diagram
MISD – Multiple Instruction, Single Data
| Description | Key Features |
|---|---|
| Multiple processors execute different instructions on the same data | Very uncommon in practice |
| Used in specialised systems for fault tolerance | Each unit checks the same input differently |
Example: Redundant systems in safety-critical environments
Multiple Instruction, Single Data Diagram
MIMD – Multiple Instruction, Multiple Data
| Description | Key Features |
|---|---|
| Multiple processors execute different instructions on different data sets | Most modern multi-core processors use this model |
| Allows full concurrent processing of independent tasks | Flexible and scalable for parallel programs |
Example: Multi-core CPUs, distributed systems, cloud computing
Multiple Instruction, Multiple Data Diagram
Summary table
| Architecture | Instruction Stream | Data Stream | Used In |
|---|---|---|---|
| SISD | Single | Single | Standard sequential processors |
| SIMD | Single | Multiple | Vector processing (e.g. GPUs) |
| MISD | Multiple | Single | Specialised fault-tolerant systems |
| MIMD | Multiple | Multiple | Multi-core processors, parallel systems |
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