Memory Access Time and Disk Access Time

This last friday we were learning about context switching, where I learn that proccesor must have his own memory so this can be done.

Context switching means that we will interrupt a process for a time, and later we will be resumng it.
(http://en.wikipedia.org/wiki/Context_switch)

I understood that this proccess is called process control block, and it is the information we need to manage a process.
(http://en.wikipedia.org/wiki/Process_control_block)

That's the reason I am talking now about access time:
Memory Access Time between a memory operation request and the time this operation completes. When reading from memory, Memory Access Time is the time from the point that the CPU places an address on the address bus and the CPU takes the data off the data bus.
(http://webster.cs.ucr.edu/AoA/Windows/HTML/SystemOrganizationa4.html)

Disk Acces Time is the time that the computer takes to procces the data request from the processor and then retrieve that data from a storage device.