ITPEC IP April 2020 Question 10

Cache memory — it sits at the top of the memory hierarchy, the fastest and the smallest storage in a computer.

Storage devices ranked by access time, fastest first:

• •Cache memory (SRAM, in or next to the CPU): a few nanoseconds
• •Main memory (DRAM): tens of nanoseconds
• •SSD (flash memory): tens of microseconds, with no moving parts
• •HDD (magnetic disk): milliseconds, spent moving the head and waiting for the disk to rotate

Cache memory exists to hide the gap between the CPU and main memory, so it must be faster than main memory.

Answer (c)

Why not others:

• •(a) HDD — the slowest of the four: every access waits for the mechanical seek and rotation
• •(b) SSD — no moving parts makes it much faster than an HDD, but flash memory is still far slower than DRAM or SRAM
• •(d) Main memory — fast, but DRAM is slower than the SRAM of the cache; that is why the cache is placed in front of it

Key rule: The memory hierarchy runs registers, cache, main memory, SSD, HDD: each step down is slower and larger, and cheaper per bit.

Computer Component · AI-written, may contain errors