Common RAM Types
 

Editor-in-Chief  :

Prof. Riazuddin
Editorial Board  :      

Fawad Saeed (IT)

 Adeel-ur-Rehman(IT)

 M. Jamil  Aslam(Physics)

 Ijaz Ahmed(Physics)
 

SRAM
Static random access memory uses multiple transistors, typically four to six, for each memory cell but doesn't have a capacitor in each cell. It is used primarily for cache.

DRAM
Dynamic random access memory has memory cells with a paired transistor & capacitor requiring constant refreshing.

FPM DRAM
Fast page mode dynamic random access memory was the original form of DRAM. It waits through the entire process of locating a bit of data by column & row & then reading the bit before it starts on the next bit. Maximum transfer rate to L2 cache is approximately 176 MBps.

EDO DRAM
Extended data-out dynamic random access memory does not wait for all of the processing of the first bit before continuing to the next one. As soon as the address of the first bit is located, EDO DRAM begins looking for the next bit. It is about five percent faster than FPM. Maximum transfer rate to L2 cache is approximately 264 MBps.

SDRAM
Synchronous dynamic random access memory takes advantage of the burst mode concept to greatly improve performance. It does this by staying on the row containing the requested bit & moving rapidly through the columns, reading each bit as it goes. The idea is that most of the time the data needed by the CPU will be in sequence. SDRAM is about 5% faster than EDO RAM & is the most common form in desktops today. Maximum transfer rate to L2 cache is approximately 528 MBps.

DDR SDRAM
Double data rate synchronous dynamic RAM is just like SDRAM except that it has higher bandwidth, meaning greater speed. Maximum transfer rate to L2 cache is approximately 1,064 MBps (for DDR SDRAM 133 MHZ).

RDRAM
Rambus dynamic random access memory is a radical departure from the previous DRAM architecture. Designed by Rambus, RDRAM uses a Rambus in-line memory module (RIMM), which is similar in size & pin configuration to a standard DIMM. What makes RDRAM so different is its use of a special high-speed data bus called the Rambus channel. RDRAM memory chips work in parallel to achieve a data rate of 800 MHz, or 1,600 MBps. Since they operate at such high speeds, they generate much more heat than other types of chips. To help dissipate the excess heat Rambus chips are fitted with a heat spreader, which looks like a long thin wafer. Just like there are smaller versions of DIMMs, there are also SO-RIMMs, designed for notebook computers.

Credit Card Memory
Credit card memory is a proprietary self-contained DRAM memory module that plugs into a special slot for use in notebook computers.

PCMCIA Memory Card
Another self-contained DRAM module for notebooks, cards of this type are not proprietary & should work with any notebook computer whose system bus matches the memory card's configuration.

CMOS RAM
CMOS RAM is a term for the small amount of memory used by your computer & some other devices to remember things like hard disk settings -- see Why does my computer need a battery? for details. This memory uses a small battery to provide it with the power it needs to maintain the memory contents.

VRAM
VideoRAM, also known as multiport dynamic random access memory (MPDRAM), is a type of RAM used specifically for video adapters or 3-D accelerators. The "multiport" part comes from the fact that VRAM normally has two independent access ports instead of one, allowing the CPU & graphics processor to access the RAM simultaneously. VRAM is located on the graphics card & comes in a variety of formats, many of which are proprietary. The amount of VRAM is a determining factor in the resolution & color depth of the display. VRAM is also used to hold graphics-specific information such as 3-D geometry data & texture maps. True multiport VRAM tends to be expensive, so today, many graphics cards use SGRAM (synchronous graphics RAM) instead. Performance is nearly the same, but SGRAM is cheaper.