Operation of processes - Operating System

Q.  Match the following list1 with list2:

a. DMA I/O -------------------------------------- 1. High speed RAM
b. Cache ---------------------------------------- 2. Disk
c. Interrupt I/O --------------------------------- 3. Printer
d. Condition code register ------------------- 4. ALU

- Published on 19 Oct 15

a. a – 2, b – 1, c – 3, d - 4
b. a – 4, b – 1, c – 3, d - 2
c. a – 2, b – 3, c – 1, d - 4
d. a – 3, b – 4, c – 2, d - 1

ANSWER: a – 2, b – 1, c – 3, d - 4


  • Nirja Shah   -Posted on 12 Nov 15
    Condition code register - Also called flag register or condition code register.
    - It is a collection of status flag bits for a processor. For e.g . FLAGS register of the x86 architecture.
    - These flags can be a part of a larger register like a program status word (PSW) register.

    Cache - a component that stores data to assist serving requests faster for that data in future
    - The data stored in cache can come from an earlier computation or the duplicate of data that was stored somewhere else.

    DMA refers to Direct memory access
    - It allows some hardware subsystems to get an access to the main system memory (RAM) while being independent of RAM
    - What would happen without DMA? - The CPU is using programmed input/output, it is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work.
    - With DMA, the CPU first initiates the transfer, then it does other operations while the transfer is in progress, and it finally receives an interrupt from the DMA controller when the operation is done.

    Programmed I/O (PIO) - It refers to the data transfers initiated by a CPU under driver software control to access registers or memory on a device.
    - The CPU issues a command then waits for I/O operations to be complete.
    - As the CPU is faster than the I/O module, the problem with programmed I/O is that the CPU has to wait a long time for the I/O module of concern to be ready for either reception or transmission of data.
    - The CPU, while waiting, must repeatedly check the status of the I/O module, and this process is known as Polling.
    - As a result, the level of the performance of the entire system is severely degraded.

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