Types of RAM
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Types of Ram and Memory
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 primarily used for cache.
Notes: short for static random access memory, and pronounced as “ess-ram.” SRAM is a type of memory that is faster and more reliable than your common DRAM (dynamic RAM). The term static is derived from the fact that it doesn’t need to be refreshed like dynamic RAM. But, DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as 10 nanoseconds. In addition, its cycle time is a lot shorter than that of DRAM, because, it does not need to pause between access. Unfortunately, it is also much more expensive to produce than DRAM. Due to its high cost, SRAM is often used only as a memory cache.
DRAM: Dynamic random access memory has memory cells with a paired transistor and capacitor requiring constant refreshing.
Notes: a type of physical memory used in most personal computers. The term dynamic indicates that the memory must be constantly refreshed (re-energized) or it will lose its contents. RAM (random-access memory) is sometimes referred to as DRAM (pronounced dee-ram) to distinguish it from static RAM [SRAM]. Static RAM is faster and less volatile than dynamic RAM, but it requires more power and it is more expensive.
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 and row and 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.
In depth – information: this is a type of DRAM that is faster than conventional DRAM.
Unlike conventional DRAM which can only access one block of data at a time, EDO RAM can start fetching the next block of memory at the same time that it sends the previous block to the CPU.
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 and 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 five percent faster than EDO RAM and 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 is 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 and 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.
CMOS RAM: CMOS RAM is a term for the small amount of memory used by your computer and some other devices to remember things like hard disk, keyboard and mouse.
Notes: this memory uses a small battery to provide it with the power it needs to maintain the memory contents.
In depth – information: CMOS (pronounced see-moss) stands for complementary metal-oxide semiconductor. This is a type of memory chip with very low power requirements. But, in PCs it operates itself by using small batteries and it was referred as CMOS RAM. This is a tiny 64-byte region of memory that uses battery power to retain data when the PC is shutdown.
VRAM: VideoRAM, also known as multiport – dynamic – random – access memory (MPDRAM). It 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 and graphics processor to access the RAM simultaneously. VRAM is located on the graphics card and it comes in a variety of formats – many of which are proprietary. The amount of VRAM is a determining factor in the resolution and color depth of the display. VRAM is also used to hold graphics-specific information such as 3D geometry data and textured maps. True multiport VRAM tends to be expensive. So today, many graphics cards uses SGRAM (Synchronous Graphics RAM) instead. Performance is nearly the same, but SGRAM is cheaper.
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