Computer Architecture and organization

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Computer Architecture and organization

• FAHIM KHATTAK
• Student of Electrical Engineering
• University of Science and Technology, Bannu

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Computer Architecture vs computer organization

Computer Architecture Computer Organization
Computer Architecture is concerned with the way hardware components are connected together to form a computer system. Computer Organization is concerned with the structure and behavior of a computer system as seen by the user.
It acts as the interface between hardware and software. It deals with the components of a connection in a system.
Computer Architecture helps us to understand the functionalities of a system. Computer Organization tells us how exactly all the units in the system are arranged and interconnected.
A programmer can view architecture in terms of instructions, addressing modes and registers. Whereas Organization expresses the realization of architecture.
While designing a computer system architecture is considered first. An organization is done on the basis of architecture.
Computer Architecture deals with high-level design issues. Computer Organization deals with low-level design issues.
Architecture involves Logic (Instruction sets, Addressing modes, Data types, Cache optimization) Organization involves Physical Components (Circuit design, Adders, Signals, Peripherals)
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Flynns classification

• M.J. Flynn proposed a classification for the
  organization of a computer system by the number
  of instructions and data items that are
  manipulated simultaneously
• The sequence of instructions read from memory
  constitutes an instruction stream.
• The operations performed on the data in the
  processor constitute a data stream.
• Flynn's classification divides computers into
  four major groups that are
• Single instruction stream, single data stream
  (SISD)
• Single instruction stream, multiple data stream
  (SIMD)
• Multiple instruction stream, single data stream
  (MISD)
• Multiple instruction stream, multiple data
  stream (MIMD)

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Flynns classification
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SISD
Where, CU  Control Unit, PE  Processing Element,
 M  Memory  
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SISD

• SISD stands for 'Single Instruction and Single
  Data Stream'. It represents the organization of a
  single computer containing a control unit, a
  processor unit, and a memory unit.
• Instructions are executed sequentially, and the
  system may or may not have internal parallel
  processing capabilities.
• Most conventional computers have SISD
  architecture like the traditional Von-Neumann
  computers.
• Parallel processing, in this case, may be
  achieved by means of multiple functional units or
  by pipeline processing.
• Instructions are decoded by the Control Unit and
  then the Control Unit sends the instructions to
  the processing units for execution.
• Data Stream flows between the processors and
  memory bi-directionally.
• Examples
• Older generation computers, minicomputers, and
  workstations

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SIMD
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SIMD

• SIMD stands for 'Single Instruction and Multiple
  Data Stream'. It represents an organization that
  includes many processing units under the
  supervision of a common control unit.
• All processors receive the same instruction from
  the control unit but operate on different items
  of data.
• The shared memory unit must contain multiple
  modules so that it can communicate with all the
  processors simultaneously.
• SIMD is mainly dedicated to array processing
  machines. However, vector processors can also be
  seen as a part of this group

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MISD
Where, M  Memory Modules, CU  Control Unit, P  
Processor Units  
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MISD

• MISD stands for 'Multiple Instruction and Single
  Data stream'.
• MISD structure is only of theoretical interest
  since no practical system has been constructed
  using this organization.
• In MISD, multiple processing units operate on one
  single-data stream. Each processing unit operates
  on the data independently via separate
  instruction stream.
• The experimental Carnegie-Mellon C.mmp computer
  (1971)

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MIMD
Where, M  Memory Module, PE  Processing Element,
 and CU  Control Unit 
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MIMD

• MIMD stands for 'Multiple Instruction and
  Multiple Data Stream'.
• In this organization, all processors in a
  parallel computer can execute different
  instructions and operate on various data at the
  same time.
• In MIMD, each processor has a separate program
  and an instruction stream is generated from each
  program
• Cray T90, Cray T3E, IBM-SP2

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The von Neumann ARCHITECTURE
Buses
CPU
So where is the Input/Output?
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von Neumann architecture

• Memory holds data, instructions.
• Central processing unit (CPU) fetches
  instructions from memory.
• Separate CPU and memory distinguishes
  programmable computer.
• CPU registers help out program counter (PC),
  instruction register (IR), general-purpose
  registers, etc.
• Both instructions and Data stored only in the
  main memory (stored program concept)
• Information fetched from memory through program
  counter (PC) register, is a machine instruction
• Information fetched through address from any
  other register is data

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The Harvard Architecture (1)

• Harvard architecture is a computer architecture
  with physically separate storage and signal
  pathways for instructions and data.

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The Harvard Architecture (2)

• In a computer with a von Neumann architecture
  (and no cache), the CPU can be either reading an
  instruction or reading/writing data from/to the
  memory.
• Both cannot occur at the same time since the
  instructions and data use the same bus system.
• In a computer using the Harvard architecture, the
  CPU can read both an instruction and perform a
  data memory access at the same time, even without
  a cache.
• A Harvard architecture computer can thus be
  faster for a given circuit complexity because
  instruction fetches and data access do not
  contend for a single memory pathway.

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The Harvard Architecture (3)

• In a Harvard architecture, there is no need to
  make the two memories share characteristics. In
  particular, the word width, timing,
  implementation technology, and memory address
  structure can differ.
• In some systems, instructions can be stored in
  read-only memory while data memory generally
  requires read-write memory.
• Instruction memory is often wider than data
  memory.

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Harvard architecture
address
CPU
data memory
PC
data
address
program/instruction memory
data
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Modified Harvard Architecture

• The Modified Harvard architecture is very like
  the Harvard architecture but provides a pathway
  between the instruction memory and the CPU that
  allows words from the instruction memory to be
  treated as read-only data.
• This allows constant data, particularly text
  strings, to be accessed without first having to
  be copied into data memory, thus preserving more
  data memory for read/write variables.
• Special machine language instructions are
  provided to read data from the instruction
  memory.
• Standards-based high-level languages, such as
  the C language, do not support the Modified
  Harvard Architecture, so that in-line assembly or
  non-standard extensions are needed to take
  advantage of it.
• Most modern computers that are documented as
  Harvard Architecture are, in fact, Modified
  Harvard Architecture.

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von Neumann vs. Harvard

• Harvard cant use self-modifying code.
• Harvard allows two simultaneous memory fetches.
• Most DSPs use Harvard architecture for streaming
  data