Random Access Memory

Posted on March 27, 2010, 12:57 am

Random Access Memory RAM Random Access Memory. RAM is where your computer stores programs that you currently use and the data you are currently working. RAM can be contrasted with the disk storage. Disk storage holds all your programs and all your data – if you work with them or not. When you turn off your computer, the contents of RAM disappear instantly, but the contents of your storage disk remain intact. RAM is sometimes contrasted with ROM. ROM (Read Only Memory) are memory chips that have information stored on those who can not be changed. What size RAM? RAM is low, both in physical size (it is stored in the chip) and the amount of data it can hold. It is much smaller than your hard drive. A typical computer came in May with 256 million bytes of RAM and a hard drive that can hold 40 billion bytes. RAM comes in the form of “discrete” (meaning separate) microchips and also as modules that plug into holes in the motherboard of the computer. These holes connect through a bus or a set of electrical paths of the processor. The hard drive on the other hand, stores data on a magnetized surface that looks like a phonograph record. Most personal computers are designed to allow you to add modules for additional RAM, to a certain ceiling. Having more RAM in your computer reduces the number of times the computer processor to read data from your hard disk, an operation that takes much longer than reading data from RAM. (RAM access time is in nanoseconds, the time to access the hard drive is in milliseconds.) Types of RAM Here are some common types of RAM: SRAM: Static Random access memory uses multiple transistors, typically four to six years for each memory cell, but does not have a capacitor in each cell. It is used primarily for cache. DRAM: Dynamic random access memory has memory cells with a transistor and capacitor requiring constant refreshing combined. FPM DRAM: Fast page mode dynamic random access memory was the original form of DRAM. He looks through the entire process of locating a bit of data by column and row and reading the bits before it starts the next bit. Maximum transfer rate of L2 cache is approximately 176 MBps. EDO DRAM: Extended data-out dynamic random access memory does not expect the full treatment of the first bit before moving to the next. Once 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 of L2 cache is approximately 264 MBps. SDRAM: Synchronous Dynamic Random Access Memory took advantage of the burst mode concept to greatly improve performance. She is staying on the line 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 required by the processor will be in order. SDRAM is about five percent faster than EDO RAM and is the most common form in desktops today. Maximum transfer rate of L2 cache is approximately 528 MBps. DDR SDRAM: Double data rate synchronous dynamic RAM is just like SDRAM, except it has a higher bandwidth, meaning greater speed. Maximum transfer rate of L2 cache is approximately 1064 MB / s (for DDR SDRAM 133 MHZ). RDRAM: dynamic random access memory Rambus is a radical change from the previous DRAM architecture. Designed by Rambus, RDRAM uses a Rambus memory module online (RIMM), which is similar in size and pin configuration for a standard DIMM. What makes RDRAM so different is its use of a special bus to high data rate called the Rambus channel. The RDRAM memory chips work in parallel to achieve a data rate of 800 MHz, or 1600 Mb / s. As they operate at high speeds, they generate more heat than other types of chips. To help dissipate excess heat Rambus chips are fitted with a heat diffuser, which resembles a long thin plate. Just as there are smaller versions of DIMMs, there are SO-RIMM, designed for laptops. Credit card memory: memory card is a property of self-contained DRAM memory module that plugs into a special connector for use in laptops. PCMCIA Memory Card: Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the configuration memory. 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 settings – see Why does my computer need a battery? For more details. This memory uses a small battery to provide the energy needed to maintain the memory contents. VRAM: Video RAM, also known as multiport memory dynamic random access (MPDRAM) is a type of RAM used specifically for video adapters or 3-D accelerators. The multiport “” A part from the fact that VRAM normally has two ports for independent access instead of one, which allows the CPU and graphics processor to access the RAM simultaneously. VRAM is located on the graphics card and comes in a variety of formats, many of which are exclusive. The amount of VRAM is a determining factor in the resolution and color depth of the screen. VRAM is also used to hold graphics-specific information such as data from the 3-D geometry and texture maps. True multiport VRAM tends to be expensive today, many graphics cards use SGRAM (synchronous graphics RAM) instead. Performance is nearly the same, but SGRAM is cheaper.