A cache is a type of high-speed memory responsible for keeping all the frequently used memory addresses in the main memory. It is a kind of Random Access Memory (RAM) that caters to the needs of another of another RAM and whose purpose is to decrease the average time it takes to fetch a "regularly accessed" address in the RAM. The main client of the cache is the central processing unit (CPU). Cache can be organized in three different ways namely direct mapping, fully associative mapping and set mapping. In direct mapping, a certain address is mapped with a single data thus if two data with the same mapped address are triggered at the same time then they tend to knock each other. In fully associative mapping, a requested address looked-up in all a specific directory. If the address is found, the address is returned to the processor, otherwise, it reports a miss. Set mapping, on the other hand, behaves like a direct mapping, only there is a specific set of location where the address will be looked at. Cache memory is I think the smallest type of RAM followed by the virtual memory and the main RAM. The major processing requirements are done using the main RAM and the computer's memory processing depends on the amount of main memory installed and supported by the OS and the computer. Virtual memory on the other hand uses a specific harddisk space to be used as a temporary storage of what the user is working.
Response:
I agree with George in saying that cache memory are scanned first by the microprocessor before actually searching the main RAM when a request is made. This enhances the searching of data as a smaller location is searched first and if a miss was reported then it is only the time when the RAM (which is definitely larger than the cache) is search. Just like if we are searching for something, we start looking at the place we think we left the thing like in a room rather than starting to look all around the house first. This definitely reduces searching time. A disk cache is also vital as this is helpful for users. One use of disk cache is when we see our list of recent documents.
Works Cited
Tyson, Jeff. How Virtual Memory Works. n.d. Web. 13 Jun 2013. < http://www.howstuffworks.com/virtual-memory.htm>
