Memory

Main Memory or RAM
RAM or Random access memory described earlier as main memory or primary storage is used to store programs and data that the CPU is presently in processing. The reason it is called “random access” memory is that data can be retrieved at random from anywhere in a RAM chips equal amounts of time. RAM is volatile memory

Volatile Memory
It means that data stored in RAM is lost when computer is switched off that is, it is temporary storage.<br>
RAM chips are often mounted on a small circuit board, such as SIMM or DIMM which is plugged into the Motherboard.

SIMM
Single in line memory module has Ram Chips only on one side. The SIMM was used with computers using a 486, early Intel Pentium, and compatible processors. SIMM is only 32-bits wide, they must be installed two at
a time when used with any 64-bit processor.

DIMM
Dual inline memory module has RAM chips on both sides. Dual In-line Memory Module, DIMM is a circuit board that holds memory chips. DIMMs have a 64-bit path because of the Pentium Processor requirements.
Because of the new bit path, DIMMs can be installed one at a time

DRAM
(Dynamic Random Access Memory) chips used for most main memory. DRAM stores its information in a cell containing a capacitor and transistor; because of this design, these cells must be refreshed with new
electricity every few milliseconds allowing the memory to keep its charge and hold the data as long as need

SRAM
(Static Random Access Memory) chips, used for some specialized purpose within main memory. Static RAM, SRAM is computer memory that requires a constant power flow in order to hold information. Power
consumption varies widely based on how frequently the memory is accessed. It is commonly only used in cache and video card memory.

ROM
Read only memory is memory from which data may retrieve, but the contents cannot be change by the user. They store instructions in permanent, or non-volatile, form. Non-volatile storage does not lose its contents when the power is turned off. Variation of ROM Chip

PROM
Programmable Read Only Memory. It is also a non-volatile storage.

EPROM
Erasable Programmable Read Only Memory. PROM cannot be changed or altered and EPROM when in use information can only be read and remain in the chip until it is erased.    

EEPROM
Electrically Erasable Programmable Read Only Memory. EEPROM chip can be erased, either within a computer or extrenally, by electric power. the process usally requires more voltage than the common +5 volts used in login circuits. 

other forms of memory
Moving data between R M and the CPU’s registers is one of the most time consuming operation a CPU must  perform, simply because RAM is much slower than the CPU. A partial problem to this solution is to include a cache memory on the micro processor chip or elsewhere on motherboard. Cache (pronounced “Cash”) is  similar to RAM except that it is extremely fast compared to normal memory and is used in a different way.

VIRTUAL MEMORY
It is a condition in which part of a program is stored on disk and is brought into memory only as needed. This features which requires, special software, uses the disk as an extension of RAM. The virtual memory program
puts as many piece of the program into RAM as possible.

VIDEO MEMORY
V(RAM) chips are used to store display images for the monitor. The amount of video memory determines how fast images appear and how many colures are available. Video memory chips are particularly desirable if you are running programs that display a lot of graphics.

FLASH MEMORY
Flash memory is non-volatile memory. That is, it retains data even when the power is turned off flesh memory can be used not only to simulate main memory but also supplement or replace hard disk drives for permanent
storage.