Question

Please help me with 2 questions in the following pictures!

DMA uses physical memory addresses as following Select one: a. Virtual addresses are written into the DMA controller, then DMA must use MMU to have the physical- to-physical translation b. Virtual addresses are written into the DMA controller, then DMA must use MMU to have the physical- to-virtual translation C. OS convert the virtual address of the intended memory buffer into a physical address and write this physical address into the DMA controller's address register, then DMA must use MMU to have the virtual- to-physical translation d. Virtual addresses are written into the DMA controller, then DMA must use MMU to have the virtual-to- physical translation A disk queue with requests for 1/0 blocks on cylinders in orders: 10, 22, 20, 2, 40, 6, 38. Assume that the disk head is initially at cylinder 18 and the head move downward. How many cylinders does Total head movement move when the elevator algorithms are used?

Answer 1

Q1.

The option (c) is the correct option.

The only reason it's correct because DMA never uses virtual address. It will always use physical address.

Q2.

Arranging request in increasing cylinder#

2 , 6 , 10 , 20 , 22 , 38 , 40

Here since the head movement is going down from 18. It will service all request down to 18 which is 10 , 6 and 2. Then it will go to the extreme end which is 0. Then again start from 0 in upward direction and service all request.

The total head movement = (18-10) +(10-6) +(6-2) +(2-0) +(20-0) +(22-20) +(38-22) (+40-38)

= 18 + 40 = 58

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