Random-Access-Memory(RAM)

Random Access Memory (RAM)

Random Access Memory (RAM) provides space for your computer to read and write data to be accessed by the CPU (central processing unit). When people refer to a computer's memory, they usually mean its RAM.

If you add more RAM to your computer, you reduce the number of times your CPU must read data from your hard disk. This usually allows your computer to work considerably faster, as RAM is many times faster than a hard disk.

RAM is volatile, so data stored in RAM stays there only as long as your computer is running. As soon as you turn the computer off, the data stored in RAM disappears.

DRAM -- Dynamic RAM

Dynamic random access memory (DRAM) is the most common kind of random access memory (RAM) for personal computers and workstations. Memory is the network of electrically-charged points in which a computer stores quickly accessible data in the form of 0s and 1s. Random access means that the PC processor can access any part of the memory or data storage space directly rather than having to proceed sequentially from some starting place. DRAM is dynamic in that, unlike static RAM (SRAM), it needs to have its storage cells refreshed or given a new electronic charge every few milliseconds. Static RAM does not need refreshing because it operates on the principle of moving current that is switched in one of two directions rather than a storage cell that holds a charge in place. Static RAM is generally used for cache memory, which can be accessed more quickly than DRAM.
DRAM stores each bit in a storage cell consisting of a capacitor and a transistor. Capacitors tend to lose their charge rather quickly; thus, the need for recharging. A variety of other RAM interfaces to the computer exist, such as EDO RAM and SDRAM.

RDRAM -- Rambus DRAM



If you are using RDRAM, make sure that all memory sockets of a channel are filled with either a memory chip or a continuity module.
RDRAM often has to be installed in pairs of the same type of memory chips.

RDRAM devices may be configured into single-, dual- or quad-channel RIMM modules. For dual-channel or quad-channel (4-channel) RDRAM chipsets and motherboards, memory module upgrades should be in matched pairs. For instance, to add 512 MByte of memory into a dual or 4-channel system, two matched 256 MByte modules should be inserted.

32-bit RIMM modules, such as RIMM 4200, 4800, and 6400 modules, can be upgraded singly on dual channel systems.


DIMM (Dual Inline Memory Module) or RIMM (Rambus Inline Memory Module)?

A: RIMM is the trademarked name for a Direct Rambus memory module.
RDRAM is available only in RIMM packages (such as 184-pin RIMMs).
RIMMs look similar to DIMMs, but have a different pin count. (Typically DIMMs are 168-pin, while RIMMs are 184-pin.) RIMMs transfer data in 16-bit chunks.


Example of RDRAM speeds include PC 800 (PC-800 or PC800) and PC 1066 (PC-1006 or PC1066).

Dual Channel RDRAM -- Dual-channel PC800 RDRAM, as found in Intel's 850 Pentium 4 chipset, provides a higher bandwidth than even PC2700 DDR-SDRAM (DDR333).



SDRAM -- Synchronous DRAM (JEDEC SDRAM)



SDRAM (synchronous DRAM) is a generic name for various kinds of dynamic random access memory (DRAM) that are synchronized with the clock speed that the microprocessor is optimized for. This tends to increase the number of instructions that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns). This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanoseconds by dividing the chip speed into 1 billion ns (which is one second). For example, an 83 MHz RAM would be equivalent to 12 ns.


DDR (Double Data Rate SDRAM)

DDR basically doubles the rate of data transfer of standard SDRAM by transferring data on the up and down tick of a clock cycle. DDR memory operating at 333MHz actually operates at 166MHz * 2 (aka PC333 / PC2700) or 133MHz*2 (PC266 / PC2100). DDR is a 2.5 volt technology that uses 184 pins in its DIMMs. It is incompatible with SDRAM physically, but uses a similar parallel bus, making it easier to implement than RDRAM, which is a different technology.