Gate CS-2011 Question Paper With Solutions

Q. 28 On a non-pipelined sequential processor, a program segment, which is a part of
the interrupt service routine, is given to transfer 500 bytes from an I/O device to
memory.

Initialize the address register
              Initialize the count to 500
        LOOP: Load a byte from device
              Store in memory at address given by address register
              Increment the address register
              Decrement the count
              If count != 0 go to LOOP

Assume that each statement in this program is equivalent to a machine instruction
which takes one clock cycle to execute if it is a non-load/store instruction. The
load-store instructions take two clock cycles to execute.
The designer of the system also has an alternate approach of using the DMA
controller to implement the same transfer. The DMA controller requires 20 clock
cycles for initialization and other overheads. Each DMA transfer cycle takes two
clock cycles to transfer one byte of data from the device to the memory.
What is the approximate speedup when the DMA controller based design is used
in place of the interrupt driven program based input-output?

Learn More:   Gate EE-2006 Question Paper With Solutions

(A) 3.4

(B) 4.4

(C) 5.1

(D) 6.7

Answer: (A)

Explanation:

Gate CS-2011 Question Paper With Solutions

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