SISD Architecture (Single Instruction, Single Data)
SISD Architecture (Single Instruction, Single Data)
Computer Architecture - Unit IV: Parallel Processing
Instituto Tecnológico de Comitán
Instructor: M. en S. Paulo Eduardo Chapela Gómez
Semester: August-December 2025
What is SISD?
- • SISD stands for Single Instruction, Single Data.
- • It is the simplest and most traditional computer architecture.
- • A single processor executes one instruction at a time on one data stream.
- • Example: A traditional sequential CPU.
How SISD Works
- • The Control Unit (CU) fetches and decodes one instruction at a time.
- • The ALU executes that instruction using data from memory.
- • The result is stored back in memory or a register.
- • Process: 1. Fetch → 2. Decode → 3. Execute → 4.Store
SISD Diagram
Typical SISD Model:
| Control Unit |
| ALU/CPU Core |
| Memory |
| Data Stream |
Examples of SISD Systems
- • Early computers: IBM 360, Intel 8086, Motorola 68000.
- • Most modern personal computers (when using a single core).
- • Sequential programs (e.g., basic C or Java code without threads).
Advantages of SISD
- 1. Simple design and control.
- 2. Easier to program - no need for synchronization.
- 3. Predictable execution time.
- 4. Lower cost and hardware complexity.
SIMD Architecture
- Single Instruction, Multiple Data
- Overview of parallel data processing.
Definition
SIMD refers to a computer architecture in which a single instruction is executed simultaneously on multiple data elements.
Key Characteristics
- One control unit
- Multiple processing units
- Executes the same instruction across multiple data points
- Highly parallel data processing
Advantages
- High performance for vector and matrix operations
- Efficient for graphics, multimedia, and scientific computing
- Reduces instruction overhead
Disadvantages
- Not suitable for tasks requiring different operations per data element
- Less flexible than MIMD architectures
- Requires data to be highly regular and parallelizable
Common Applications
- Image and video processing
- Deep learning and AI acceleration
- Vectorized numerical computations
- GPU operations
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