DMA

Question 1

A hard disk is connected to a 50 MHz processor through a DMA controller. Assume that the initial set-up of a DMA transfer takes 1000 clock cycles for the processor, and assume that the handling of the interrupt at DMA completion requires 500 clock cycles for the processor. The hard disk has a transfer rate of 2000 Kbytes/sec and average block transferred is 4 K bytes. What fraction of the processor time is consumed by the disk, if the disk is actively transferring 100% of the time?

A
Theory Explanation.
Computer-OrganizationDMAGATE 1996
Question 2

Which of the following requires a device driver?

A
Register
B
Cache
C
Main memory
D
Disk
Computer-OrganizationDMAGATE 2001
Question 2 Explanation: 
Disk driver is software which enables communication between internal hard disk (or drive) and computer.
Question 3
 Consider a computer system with DMA support, The DMA module is transferring one 8-bit character in one CPU cycle from a device to memory through cycle stealing at regular intervals. Consider a 2 MHz processor. If 0.5% processor cycles are used for DMA, the data transfer rate of the device is ______ bits per second.
A
80,000
Computer-OrganizationDMAGATE 2021 CS-Set-2Video-Explanation
Question 3 Explanation: 
Question 4

A hard disk with a transfer rate of 10 Mbytes/ second is constantly transferring data to memory using DMA. The processor runs at 600 MHz, and takes 300 and 900 clock cycles to initiate and complete DMA transfer respectively. If the size of the transfer is 20 Kbytes, what is the percentage of processor time consumed for the transfer operation?

A
5.0%
B
1.0%
C
0.5%
D
0.1%
Computer-OrganizationDMAGATE 2004
Question 4 Explanation: 
Clock cycle time = 1/600 × 10-6 (time = 1/frequency)
For DMA initiation and completion total 1200 cycles is required. So total time will be = 1200 × 1/600 × 10-6 = 2μs
Disk transfer rate = 10MB/s
1B = 1/107 s
So, total transfer 20KB time taken will be,
20 × 103 × 1/(107) s
= 2000μs
∴ Percentage of processor time consumed is,
2/2+2000 × 100 = 0.1%
There are 4 questions to complete.

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