'read'command for data to retrieve from magnetic disk. describe the
resulting mechanical movement and the movement of data.

Hello Amanda12,

There is a pretty good explanation of the operation of disk drives as
part of a simulation paper at
  http://www.hpl.hp.com/research/ssp/papers/IEEEComputer.DiskModel.pdf
The paper was written in 1994 and some of the information is dated
(e.g., capacity of the disk drive) but the basic information is still
correct.

From that paper, the "read" portion can be summarized as follows:

Figure 2 has a time line of the read operation, showing the sequence
of disk operations which are basically:
 o [D] disk controller interprets the command from the computer
 o [M] seek - reposition the heads to the cylinder with the data
 o [M] rotational latency - wait for the data to appear under the heads
 o [D/M] transfer the off the disk into memory on the disk controller
 o [D] access the bus (e.g., SCSI, ATA) to transfer data to the computer
The notation [D} refers to data transfer, [M] refers to mechanical
movement, and [D/M] refers to both. The timeline also shows a "head
switch" where it may be necessary to move the heads to read all the
data if the disk supports large or chained data transfers (sizes
greater than a single disk block).

Figure 1 has an illustration of the mechanical assembly of a disk drive showing:
 o spindle and (one or more) platters
 o arms and arm assembly moving across the platters
 o heads (one per platter surface) attached to the arms
This also shows in a simple form the concepts of cylinders, tracks,
and sectors of data on the disk.

For further information, try seach phrases such as
  explain disk drive mechanical operation
  disk drive mechanical operation tutorial
or add more general phrases such as
  encyclopedia
  "how it works"
and so on.

If you need more specific information for your answer - please use a
clarification request.

  --Maniac