Wednesday, October 10, 2012

What is RAM (Memory)

Memory is the workspace for the processor. It is a temporary storage area where the programs and data being operated on by the processor must reside. Memory storage is considered temporary because the data and programs remain there only as long as the computer has electrical power or is not reset. Before the computer is shut down or reset, any data that has been changed should be saved to a more permanent storage device (usually a hard disk) so it can be reloaded into memory in the futur


Memory often is called RAM, for random access memory. Main memory is called RAM because you can randomly (as opposed to sequentially) access any location in memory. This designation is somewhat misleading and often misinterpreted. Read-only memory (ROM), for example, is also randomly accessible, yet is usually differentiated from the system RAM because it maintains data without power and can’t normally be written to. Although a hard disk can be used as virtual random access memory, we don’t consider that RAM either.

Over the years, the definition of RAM has changed from a simple acronym to become something that means the primary memory workspace the processor uses to run programs, which usually is constructed of a type of chip called dynamic RAM (DRAM). One of the characteristics of DRAM chips (and therefore most types of RAM in general) is that they store data dynamically, which really has two meanings. One meaning is that the information can be written to RAM repeatedly at anytime. The other has to do with the fact that DRAM requires the data to be refreshed (essentially rewritten) every few milliseconds or so; faster RAM requires refreshing more often than slower RAM. A type of RAM called static RAM (SRAM) does not require the periodic refreshing. An important characteristic of RAM in general is that data is stored only as long as the memory has electrical power.
RAM can refer to both the physical chips that make up the memory in the system and the logical mapping and layout of that memory. Logical mapping and layout refer to how the memory addresses are mapped to actual chips and what address locations contain which types of system information.
Memory temporarily stores programs when they are running, along with the data being used by those programs. RAM chips are sometimes termed volatile storage because when you turn off your computer or an electrical outage occurs, whatever is stored in RAM is lost unless you saved it to your hard drive. Because of the volatile nature of RAM, many computer users make it a habit to save their work frequently. Many software applications perform periodic saves automatically in order to minimize the potential for data loss.
Physically, the main memory in a system is a collection of chips or modules containing chips that are usually plugged into the motherboard. These chips or modules vary in their electrical and physical designs and must be compatible with the system into which they are being installed to function properly.
To better understand physical memory in a system, you should understand what types of memory are found in a typical PC and what the role of each type is. Three main types of physical memory are used in modern PCs.
■ ROM—Read-only memory
■ DRAM—Dynamic random access memory
■ SRAM—Static RAM

The only type of memory you normally need to purchase and install in a system is DRAM. The other types are built in to the motherboard (ROM), processor (SRAM), and other components such as the video card, hard drives, and so on.

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