RAM
From Extreme Overclocking
RAM (Random Access Memory) is very fast memory in computer components used to store frequently used data where it can be quickly recalled. However, once RAM loses its power, all data is lost, and for this reason it is known as volatile storage.
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System RAM
Types of RAM
DRAM
Dynamic Random Access Memory is comprised of "memory cells"; a paired transistor and capacitor which needs to be frequently refreshed, before "emptying". This is the basis for most ram, where it all started.
EDO DRAM
Extended Data-Out Dynamic Random Access Memory. Rather than completing the processing of the first bit in sequence, as soon as the address of the first bit is located, EDO DRAM begins looking for the next bit.
SDRAM
Synchronous Dynamic Random Access Memory stays on the row containing the requested bit moving then through the columns, reading each bit as it goes. The data needed by the CPU, for the most part, will be in sequence. For this reason, SDRAM is slightly faster than EDO RAM and is the most common form in desktops today.
DDR SDRAM
Double Data Rate SDRAM is technically no different than regular SDRAM, but rather a technology applied to it. Instead of only sending and receiving data on the high points of the transmission, it uses both the high and the low, effectively doubling the rate at which data is transferred.
DDR2 RAM
Used in Intel (Socket 775) systems as well as AMD (socket AM2, or socket F). DDR2 is offers both greater clock frequencies and significantly greater theoretical bandwidth while consuming less power than DDR. DDR2 has been well developed to provide a wide range of low latency and high clocking DDR2 memory. Currently (Q2 2007) DDR2 is cheaper than DDR, as a result of its adoption as the standard memory platform for almost all new systems.
RDRAM
Rambus Dynamic Random Access Memory uses a Rambus in-line memory module (RIMM). While it looks similar to normal DIMMs, RDRAM is quite different. Its use of a high-speed bus, as well as chips that work in parallel, allows for the data rate of the RAM to be significantly higher than that of typical RAM, typically 800 MHz. RDRAM is used on the following Intel chipsets: 860, 850E, 850, 840, 820E, and 820.
SODIMM
While technically this is not a different form of ram, it is a different DIMM, used in laptop motherboards. They are generally half the size of a regular DIMM, and can have less/more contacts, but they still are based off of the other forms of RAM.
LATENCIES
Latencies are the delays the RAM has before it can give you data. The lower these latencies are, the better. Regular DDR has latencies as low as CAS2, meaning the RAM can access the CAS in 2 clocks. The latencies on DDRII are a little higher, to compensate for this it runs at much higher frequencies.
