Assume the following computer system. The I/O device currently holds 10MB of dat

Question

Assume the following computer system. The I/O device currently holds 10MB of data to be transferred to the main memory. Each data transfer between the I/O device and the I/O controller takes lOOps. Each data transfer using the internal bus takes 100 mu s The I/O device and the I/O controller are connected by 16-parallel wires (16 bits can be transferred in one shot). The I/O controller, the processor and the memory are connected by 16-parallel wires (16 bits can be transferred in one shot). Each context switching takes the processor 50 mus. Each interrupt transfers 16bits while DMA can transfer any number of bits (but a multiple of 16 bits) in one DMA transfer session. Ignore any other overhead How long will it take to complete data transfer using interrupt and DMA? Note: B - "byte" b - "bit" M= 106 1 second - 1,000ms and I ms - 1,000mus

Explanation / Answer

Here are the short summary related to Direct Memory Access (DMA)

Summary related to Interrupt Handling

CPU issues read command

I/O module gets data from I/O device = Total (100 us x 10 MB)

where 10 MB = 10 x 10^6 bits

1 shot = 16 bits

Therefore, 10x10^6 bits = (10x10^6)/16 shots.

[(10x10^6)/16 x 100us] = 'Time' = [(10x10^6)/16 x 10^(-4)]sec = 62.5s.

Goes to CPU = context switch = 50us+'Time'

using Interrupt = Each Interrupt = 16 bits

[(10x10^86)/16]Interrupts.

Therefore, Overhead = [50 x (10x10^16)/16]

when CPU reuests data = 100+50+Time + [50 x (10x10^6)/16]us

& I/o module transfer its = 50us + 62.5sec +31250000 us

= 0.00015sec+62.5+31.25sec

= 93.75 seconds

But with DMA = 100+50+Time+[50 x (10x10^6)/16] us

= 150us+ 62.5s+500sec

= 0.00015+62.5s+500s

=562.5 seconds

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