Small fast memory, big slow memory

Computing · Computer Systems · ages 18-19

Name ______________________ Date ____________

A loop reuses the same value many times. Which locality is that?
- Temporal locality
- Spatial locality
- No locality
Which order lists the layers from fastest to slowest?
- Main memory, caches, registers, disk
- Registers, caches, main memory, disk
- Disk, main memory, caches, registers
Spatial locality means touching neighbours next.
Circle one: True False
A loop reads cells 0, 1, 2, 3 in order. Which locality does it use?
- Spatial locality
- Temporal locality
- Neither locality
Why can column by column run several times slower on the same data?
- It visits fewer cells
- It sorts the array first
- It jumps across rows
Which layer is the smallest and fastest?
- Main memory
- Registers
- Disk
Loop A steps through neighbours in order. Loop B jumps across rows over the same data. Which wins?
- Loop A reuses each cache line
- Loop B, because jumping skips cells
- They always tie
A student says column by column must be faster because columns look shorter. What is the mistake?
- Row order uses more memory
- Cache lines only hold columns
- Order decides, not looks

Answer key

For grown-ups. Fold this page away before handing over the rest.

Temporal locality · Reuse of the same value is reuse over time.
Registers, caches, main memory, disk · Speed falls at each step down the stack.
True · Neighbour-next access is the spatial kind.
Spatial locality · Ordered cells are neighbours, and neighbours mean spatial.
It jumps across rows · Jumps across rows waste each cache line.
Registers · Registers top the stack for speed.
Loop A reuses each cache line · Ordered visits reuse each line; jumps waste them.
Order decides, not looks · Looks never decide; visit order decides.