DRAM(dynamic random access memory) :- You can expand the memory in a computer by adding DRAM chips.People use DRAM to expand the memory in the computer because it's cheaper than any other type of memory.Dynamic RAM is less complex to manufacture.Dynamic refers to the memory chips' need for a constant update signal also known as refresh memory in order to keep the information that is written there.If this signal is not received every so often, the information will cease to exist.
SRAM(static random access memory) :- Static random access memory doesn't require a refresh signal like DRAM.The chips are more complex and are thus more expensive.SRAM is faster than DRAM(DRAM access times come in at 80nanoseconds(ns) or more but SRAM has access times of 15 to 20 ns).SRAM is often used for cache memory.
ROM(read-only memory) :- ROM is called read only because it can't be written to.IF once information has been written to the ROM then it can't be changed.it is only used to store the computer's BIOS, because BIOS information does not change.The system ROM enables the computer to "pull itself up by its bootstraps," or boot the Pc.
CMOS :- CMOS is a special kind of memory that stores the BIOS configuration settings.CMOS memory is powered by a small battery so the settings are retained when the computer is shut off.The BIOS keeps the information about which hard drive types are configured for this computer to use, which drive it should look for boot sectors and so on.CMOS memory is usually not upgradeable in terms of its capacity.
