In the case of a CPU cache, it is faster because it's on the same die as the processor. In other words, the requested data doesn't have to be bussed over to the processor; it's already there.

In the case of the cache on a hard drive, it's faster because it's in solid state memory, and not still on the rotating platters.

In the case of the cache on a web site, it's faster because the data has already been retrieved from the database (which, in some cases, could be located anywhere in the world).

So it's about locality, mostly. Cache eliminates the data transfer step.

Locality is a fancy way of saying data that is "close together," either in time or space. Caching with a smaller memory works because typically a relatively small amount of the overall data is the data that is being accessed the most often.

Further Reading
Cache (Computing) on Wikipedia

In the case of a CPU cache, it is faster because it's on the same die as the processor. In other words, the requested data doesn't have to be bussed over to the processor; it's already there.

In the case of the cache on a hard drive, it's faster because it's in solid state memory, and not still on the rotating platters.

In the case of the cache on a web site, it's faster because the data has already been retrieved from the database (which, in some cases, could be located anywhere in the world).

So it's about locality, mostly. Cache eliminates the data transfer step.

Locality is a fancy way of saying data that is "close together," either in time or space. Caching with a smaller, faster (but generally more expensive) memory works because typically a relatively small amount of the overall data is the data that is being accessed the most often.

Further Reading
Cache (Computing) on Wikipedia

In the case of a CPU cache, it is faster because it's on the same die as the processor. In other words, the requested data doesn't have to be bussed over to the processor; it's already there.

In the case of the cache on a hard drive, it's faster because it's in solid state memory, and not still on the rotating platters.

In the case of the cache on a web site, it's faster because the data has already been retrieved from the database (which, in some cases, could be located anywhere in the world).

So it's about locality, mostly. Cache eliminates the data transfer step.

Cache is smaller than the device it is caching for reasons of locality. Locality is a fancy way of saying data that is "close together," either in time or space. Caching with a smaller memory works because typically a relatively small amount of the overall data is the data that is being accessed the most often.

In the case of a CPU cache, it is faster because it's on the same die as the processor. In other words, the requested data doesn't have to be bussed over to the processor; it's already there.

In the case of the cache on a hard drive, it's faster because it's in solid state memory, and not still on the rotating platters.

In the case of the cache on a web site, it's faster because the data has already been retrieved from the database (which, in some cases, could be located anywhere in the world).

So it's about locality, mostly. Cache eliminates the data transfer step.

Locality is a fancy way of saying data that is "close together," either in time or space. Caching with a smaller memory works because typically a relatively small amount of the overall data is the data that is being accessed the most often.

Further Reading
Cache (Computing) on Wikipedia