Method of dynamically controlling cache size

A method of operating a power saving cache comprising:

• using circuitry to dynamically reduce the logical size of the cache in order to save power by powering off selected areas of the cache;
• determining an optimum size for the cache for balancing power and performance given a set of power and performance criteria;
• and
• maintaining coherency of data in the cache, as the size of the cache is altered. by ensuring that copies of all data elements in the cache exist in an area of the cache not powered off.

A method of operating a power saving cache, wherein the cache includes data and some of the data in the cache is modified data, the method comprising:

• using circuitry to dynamically reduce the logical size of the cache in order to save power;
• maintaining integrity of the data as the size of the cache is altered;
• powering off sections of the cache;
• wherein the step of maintaining integrity of the data includes the step of, before powering off one of the sections of the cache, saving any modified data in said one section of the cache and ensuring that copies of all data elements in the cache exist in sections of the cache not powered off;
• and
• further comprising the step of determining an optimum size for the cache given a set of power and performance criteria, and wherein the step of using circuitry includes the step of using circuitry to reduce the size of the cache to said optimum size.