Give two reasons why caches are useful. What problems do they solve? What problems to they cause? If a cache can be made as large as the device for which caching (for instance, as large as a disk), why not make it that large and eliminate the device?
1. Caches allow faster access to data by storing data in a physically faster device (e.g. memory instead of disk).
2. Caches reduce the cost of finding data by requiring only a small number of items be searched.
3. Caches reduce the load on a slow physical devices, by handling most accesses to data on a faster, more capable device.
Caches solve the problem of slow data access, by keeping needed data in a cheap-to-access place.
Caches cause consistency problems, because the real data (for example, on disk) may be different than the cache.
Making a cache as large as the device may be useful if it can be made fast. However, the device is still needed to store data when power is turned off.