Dictionary of Computers - cache memory

The cache memory may be constructed from SRAM, which is faster but more expensive than the normal DRAM. Most programs access the same instructions or data repeatedly. If these frequently used instructions and data are stored in a fast-access SRAM memory cache, the program will run more quickly. In other cases, the memory cache is normal DRAM, but is used to store frequently used instructions and data that would normally be accessed from backing storage. Access to DRAM is faster than access to backing storage so, again, the program runs more quickly. This type of cache memory is often called a disk cache.

Read cache is used to store copies of data and instructions that are retrieved from main memory or mass storage. If the central processing unit (CPU) needs to access the same data or instructions again, it can use the copy in read cache. This is much faster the going back to main memory or mass storage again. Write cache is a temporary store for data that needs to be written to main memory or mass storage. The CPU can move the data into cache very quickly, and then continue executing instructions. The data is subsequently moved to its permanent location by the cache controller, a process that takes more time because main memory and mass storage devices are much slower to access than cache memory.

There are different levels of cache. Level one cache is the fastest and most expensive, and is positioned the closest to the CPU. Level two cache is slower, but cheaper, and usually found in larger quantities. Modern PCs are technically capable of having level three cache. This is slower and cheaper than level one or two.