RAM
Random Access Memory abbreviation RAM work as a main memory of a computer where the operating system, application programs and data in current use are kept so they can be quickly reached by the device's processor.
The purpose of RAM is to provide quick read and write access to a storage device. Your computer uses RAM to load data because it's much quicker than running that same data directly off of a hard drive. Data remains in RAM as long as the computer is running. When the computer is turned off, RAM loses its data. When the computer is turned on again, the OS and other relevant files are once again loaded into RAM from secondary storage.
There are two types of RAM differ in the technology they use to hold data, with Dynamic Random Access Memory (DRAM) being the more common type. In terms of speed, Static Random Access Memory (SRAM) is faster.
ROM
Read-Only Memory or ROM is a storage medium that is used with computers and other electronic devices. As the name indicates, data has been prerecorded on the memory. Once data has been written onto a ROM chip, it cannot be removed and can only be read.
Unlike RAM, ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile. Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer.
A variation of a ROM is a Programmable Read-Only Memory (PROM). PROMs are manufactured as blank chips on which data can be written with a special device called a PROM programmer.
Cache
The Cache Memory is the memory which is very nearest to the CPU that a computer microprocessor can access more quickly than it can access regular RAM.
A computer can have several different levels of cache memory. The level numbers refers to distance from CPU where Level 1 is the closest. All levels of cache memory are faster than RAM. The cache closest to CPU is always faster but generally costs more and stores less data then other level of cache.
The cache memory works according to various algorithms, which decide what information it has to store. These algorithms work out the probability to decide which data would be most frequently needed. This probability is worked out on the basis of past observations.
