Managing cache

How to manage cache efficiently?

Temporal locality

copy data into cache when accessed

Spatial locality

copy 2k block of data including accessed data item

How to choose range of addresses to copy?

Might choose data from addr - delta to addr + delta

where delta is 2k-1

However, this is not so convenient to manage

Instead, use all addresses with same upper n-k bits

Example:

Want to access data with address A31-0.

Copy 32 bytes with addresses:

A31-5 00000

A31-5 00001

A31-5 00010

. . .

A31-5 11111

These 32 bytes are called a cache line.

The upper 27 bits are the tag.