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Engineering LibreTexts

1.9 Multiprocessor and Multicore Systems

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  • MultiProcessor System 

    Two or more processors or CPUs present in same computer, sharing system bus, memory and I/O is called MultiProcessing System. It allows parallel execution of different processors. These systems are reliable since failure of any single processor does not affect other processors. A quad-processor system can execute four processes at a time while an octa-processor can execute eight processes at a time. The memory and other resources may be shared or distributed among processes.


    Multiple processors, each with their own cache
    Figure \(\PageIndex{1}\): Symmetric multiprocessing system. ("Symmetric multiprocessing system" by Multiple ContributorsWikipedia Commons is licensed under CC BY-SA 3.0)

    Advantages :

    • Since more than one processor are working at the same time, throughput will get increased.
    • More reliable since failure in one CPU does not affect other.
    • It needs little complex configuration.
    • Parallel processing (more than one process executing at same time) is achieved through MultiProcessing.

    Disadvantages :

    • It will have more traffic (distances between two will require longer time).
    • Throughput may get reduced in shared resources system where one processor using some I/O then another processor has to wait for its turn.
    • As more than processors are working at particular instant of time. So, coordination between these is very complex.

    Multicore System

    A processor that has more than one core is called Multicore Processor while one with single core is called Unicore Processor or Uniprocessor. Nowadays, most of systems have four cores (Quad-core) or eight cores (Octa-core). These cores can individually read and execute program instructions, giving feel like computer system has several processors but in reality, they are cores and not processors. Instructions can be calculation, data transferring instruction, branch instruction, etc. Processor can run instructions on separate cores at same time. This increases overall speed of program execution in system. Thus heat generated by processor gets reduced and increases overall speed of execution.

    Multicore systems support MultiThreading and Parallel Computing. Multicore processors are widely used across many application domains, including general-purpose, embedded, network, digital signal processing (DSP), and graphics (GPU). Efficient software algorithms should be used for implementation of cores to achieve higher performance. Software that can run in parallel is preferred because the desire is to achieve parallel execution with the help of multiple cores.


    Figure \(\PageIndex{1}\): Quad Core Processor. ("Diagram of a generic dual-core processor " by Multiple ContributorsWikipedia Commons is licensed under CC BY-SA 3.0)

    Advantages :

    • These cores are usually integrated into single IC (integrated circuit) die, or onto multiple dies but in single chip package. Thus allowing higher Cache Coherency.
    • These systems are energy efficient since they allow higher performance at lower energy. A challenge in this, however, is additional overhead of writing parallel code.
    • It will have less traffic(cores integrated into single chip and will require less time).

    Disadvantages :

    • Dual-core processor do not work at twice speed of single processor. They get only 60-80% more speed.
    • Some Operating systems are still using single core processor.
    • OS compiled for multi-core processor will run slightly slower on single-core processor

    Adapted from:
    "Difference between MultiCore and MultiProcessor System" by GaneshchowdharysadanalaGeeks for Geeks is licensed under CC BY-SA 4.0

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