Question

Got asked in an interview. They asked to order the following in terms of speed:

• CPU register access,
• Context switch
• Memory access
• Disk seek.

pretty sure the disk seek is the slowest and register access is the fastest, but not quite sure about the two in between. Can anyone explain it a bit?

Answer 1

I happened to find a surprisingly good answer on Yahoo!:

Fastest to slowest:

1. CPU
2. Memory
3. Context switching
4. Disk

Although:

Disk access may be significantly faster at times due to caching … so
can memory access (CPUs sometimes manage a caches from main memory to
help speed up access and avoid competition for the bus).

Memory access could also be as slow or slightly slower than disk
access at times, due to virtual memory page swapping.

Context switching needs to be extremely fast in general … if it was
slow then your CPU could begin to spend more time switching between
processes than actually performing meaningful work when several
processes are running concurrently.

Register access is nearly instantaneous.

(emphasis mine)

I agree with that answer.