SDRAM Short for Synchronous DRAM, a new type of DRAM that can run at much higher clock speeds than conventional memory. SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 133 MHz, about three times faster than conventional FPM RAM, and about twice as fast EDO DRAM and BEDO DRAM. SDRAM is replacing EDO DRAM in many newer computers

Today's fastest Pentium systems use CPU buses running at 100 MHz, so SDRAM can keep up with them, though barely. Future PCs, however, are expected to have CPU buses running at 200 MHz or faster. SDRAM is not expected to support these high speeds which is why new memory technologies, such as RDRAM and SLDRAM, are being developed.
Pentium III Intel builds on the technology it developed with the Pentium II microprocessors. The Pentium III processor comes with a Synchronized Dynamic Random Access Memory (SDRAM), allowing for an extremely fast transfer of data between the microprocessor and the memory. 70 new instructions, called Streaming SIMD Extensions, enhance multimedia and 3D performance. An advanced transfer cache and system buffering are able to meet higher data bandwidth requirements.
  • Dual independent bus (DIB) architecture
  • 100 MHz front-side bus speed
  • A multi-transaction system bus
  • MMX support
UMA (1) Short for Unified Memory Architecture. A computer that has graphics chips built into the motherboard that use part of the computer's main memory for video memory is said to have Unified Memory Architecture.

(2) Short for upper memory area, a synonym for high memory.
DRDRAM RDRAM (Rambus Dynamic Random Access Memory) is a memory subsystem that promises to transfer up to 1.6 billion bytes per second. The subsystem consists of the random access memory (RAM), the RAM controller, and the bus (path) connecting RAM to the microprocessor and devices in the computer that use it. Direct Rambus (DRDRAM), a technology developed and licensed by the Rambus Corporation, is the latest version and is expected to help accelerate the growth of visually intensive interfaces such as 3-D, interactive games, and streaming multimedia. Rambus is intended to replace the current main memory technology of dynamic random access memory (DRAM). Much faster data transfer rates from attached devices such as videocams using FireWire and the Accelerated Graphics Port (AGP) make it important to reduce the bottleneck in getting data into the computer, staging it in RAM, and moving it throught the microprocessor and to the display or other output devices.

Direct Rambus (DRDRAM) provides a two-byte (16 bit) bus rather than DRAM's 8-bit bus. At a RAM speed of 800 megahertz (800 million cycles per second), the peak data transfer rate is 1.6 billion bytes per second. Direct Rambus uses pipelining to move data from RAM to cache memory levels that are closer to the microprocessor or display. Up to eight operations may be underway at the same time. Rambus is designed to fit into existing motherboard standards. The components that are inserted into motherboard connections are called Rambus in-line memory modules (RIMMs). They can replace conventional dual in-line memory module.

An alternative to DRDRAM is SyncLink DRAM (SDRAM).
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.
DRAM 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. These include: EDO RAM and SDRAM.

SRAM SRAM (static RAM) is random access memory (RAM) that retains data bits in its memory as long as power is being supplied. Unlike dynamic RAM (DRAM), which stores bits in cells consisting of a capacitor and a transistor, SRAM does not have to be periodically refreshed. Static RAM provides faster access to data and is more expensive than DRAM. SRAM is used for a computer's cache memory and as part of the random access memory digital-to-analog converter on a video card.
RAM RAM (random access memory) is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor. RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM. However, the data in RAM stays there only as long as your computer is running. When you turn the computer off, RAM loses its data. When you turn your computer on again, your operating system and other files are once again loaded into RAM, usually from your hard disk.

RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, but can only keep so many facts in view at one time. If short-term memory fills up, your brain sometimes is able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. Unlike the hard disk which can become completely full of data so that it won't accept any more, RAM never runs out of memory. It keeps operating, but much more slowly than you may want it to.

How Big is RAM?

RAM is small, both in physical size (it's stored in microchips) and in the amount of data it can hold. It's much smaller than your hard disk. A typical computer may come with 32 million bytes of RAM and a hard disk that can hold 4 billion bytes. RAM comes in the form of "discrete" (meaning separate) microchips and also in the form of modules that plug into holes in the computer's motherboard. These holes connect through a bus or set of electrical paths to the processor. The hard drive, on the other hand, stores data on a magnetized surface that looks like a phonograph record.

Today's personal computers come with 16 or more megabytes of RAM, usually increasing in multiples of 8 megabytes. Users of graphic applications usually need 32 or 64 megabytes of memory. Most personal computers are designed to allow you to add additional RAM modules up to a certain limit (for example, up to 64 or 128 megabytes). Having more RAM in your computer reduces the number of times that the computer processor has to read data in from your hard disk, an operation that takes much longer than reading data from RAM. (RAM access time is in nanoseconds; hard disk access time is in milliseconds.)

Why Random Access?

RAM is called "random access" because any storage location can be accessed directly. Originally, the term distinguished regular core memory from offline memory, usually on magnetic tape in which an item of data could only be accessed by starting from the beginning of the tape and finding an address sequentially. Perhaps it should have been called "nonsequential memory" because RAM access is hardly random. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. A term IBM has preferred is direct access storage or memory. Note that other forms of storage such as the hard disk and CD-ROM are also accessed directly (or "randomly") but the term random access is not applied to these forms of storage.

In addition to disk, floppy disk, and CD-ROM storage, another important form of storage is read-only memory (ROM), a more expensive kind of memory that retains data even when the computer is turned off. Every computer comes with a small amount of ROM that holds just enough programming so that the operating system can be loaded into RAM each time the computer is turned on.