Disk Controller

Direct Memory Access (DMA)
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Direct Memory Access (DMA)

Regardless of whether a CPU does or does not have memory-mapped I/O, it needs to address the device controllers to exchange data with them. The CPU can request data from an I/O controller one byte at a time but doing so wastes the CPU's time, so a different scheme, called

Disk Arm Scheduling Algorithms
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Disk Arm Scheduling Algorithms

Now we will consider some issues related to disk drivers in general. First, look at how long it takes to read or write a disk block. The time needed is determined by three factors:For most disks, the seek time dominates the other two times, so reducing the mean seek time can improve system performance considerably.

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