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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