Chapter 6: Allison Hamann, Chris Barile

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=876437

Sector Cache

A. Organziation

1) Sectors
2) Subsectors
3) Validity Bit

B. Load Procedure

1) Sector miss
2) Subsector miss

C. Advantages

Sector Caches are organized into sectors, which correspond to sectors of the main storage. Sectors are then organized into subsectors, which are similar to cache lines. Each subsector has a "validity bit" which tells whether or not that subsector has been loaded into cache from the main storage.

When a process requests data that is not in the cache, a cache sector is assigned to the sector on the main storage device where the requested data is stored. Then a portion of that sector, known as the subsector, is loaded into the cache. The subsector's validity bit is then set to reflect that it has been loaded from the main storage.

One reason for this approach is that programs are generally organized in contiguous blocks on disk. Another is that data is first looked up by sector, and then by subsector, which means that it can be found much quicker, and the hardware to do the simultaneous comparison of tags is less expensive.