Memory is a computer system's primary workspace. It works in one behind the other with the CPU, or microprocessor, to store data, programs, and processed information that can be made immediately and directly accessible to the CPU or to other system devices. Memory is central to a computer's operation because it forms the critical link between software and the CPU. Computer memory also determines the size and number of programs that can be run simultaneously, and helps to optimize the capabilities of powerful microprocessors.

RAM (Random Access Memory) Internally, computer memory is arranged as a matrix of "memory cells" laid out in rows and columns, like squares on a checkerboard. Each memory cell is used to store a bit of data, which can be instantaneously retrieved by indicating the row and column location (or address) of the data. Because these bits of data can be individually accessed, retrieved, and modified at random, the type of main memory used in computers is called random access memory. RAM is a volatile form of memory, which means that it must have power in order to retain data.

When the power is turned off, data in RAM is lost. Contrast this to other storage media such as disks, tapes, and CDs that retain data even without power. There are many different kinds of RAM, each with its own features and benefits. For instance Extended Data Out (EDO) allows back-to-back memory accesses to occur much faster because EDO is easy to implement, it has gained wide acceptance in a very short span of time. A computer system must be designed to support EDO in order to make use of the extra efficiency it offers. EDO memory in a system that doesn't support it will still work, but there will be no performance increase.

Dynamic RAM (DRAM) is the most common type of computer memory. A bank of memory modules using DRAM chips usually forms the core of a computer's main memory. The system uses this memory to temporarily store programs, data, and processed information that moves to and from the processor, video card, and other peripherals. It is called dynamic RAM because it must be re-energized hundreds of times each second in order to retain data in its memory cells.

It has to be refreshed because its memory cells are designed around tiny capacitors that store electrical charges, these capacitors work like very tiny batteries and will gradually lose their stored charges if they are not re-energized. Graph provided by Kingston Memory. Synchronous DRAM (SDRAM) is another form of memory developed shortly after EDO. This technology is a more radical innovation that it synchronizes itself with the system clock that controls the CPU.

Being synchronized with the processor eliminates timing delays and makes the memory retrieval process much more efficient. It uses a clock to synchronize signal input and output on a memory chip. The clock is coordinated with the CPU clock so the timing of the memory chips and the timing of the CPU are synchronized. In pure speed tests, SDRAM is about 50 percent faster than EDO memory, with actual performance gains of around 25 percent. There is also the Double data rate SDRAM (DDR or SDRAM II) Which is a faster version of SDRAM that is able to read data on both the rising and the falling edge of the system clock, thus doubling the data rate of the memory chip. Left: A Rambus Memory from Kingston Memory Rambus (RDRAM) is a unique new design developed by a company called Rambus Inc.

RDRAM is extremely fast and uses a narrow, high-bandwidth channel to transmit data at speeds about ten times faster than standard DRAM. There are two types of Rambus memories, concurrent and direct. Concurrent RDRAM is based on the fundamental design of the standard RDRAM yet is enhanced to increase speed and performance. Direct RDRAM is also based on RDRAM, yet through additional enhancements will be even faster than concurrent RDRAM.

Both RDRAM and Concurrent RDRAM technology are not currently utilized for PC main memory, but targeted as memory for various consumer, workstation, and PC multimedia applications like Nintendo 64 video game systems and Creative Labs PC add-in cards. In late 1996, Rambus agreed to a development and license contract with Intel that will lead to Intel's PC chip sets supporting Rambus memory starting in 1999. As a result, Direct RDRAM has the potential to become the prevalent technology for PC main memory from 1999 on. SyncLink memory (SLDRAM) is a joint effort DRAM that may be the closest speed competitor with Rambus.

Development is coordinated through a combination of twelve DRAM manufacturers and system companies. SLDRAM is an enhanced line extension of SDRAM architecture that extends the current four-bank design to 16 banks. SLDRAM is currently in the development stage and is scheduled for production in 1999. The following table shows the comparison of commonly used RAM. EDO SDRAM DDR SDRAM SLDRAM Direct RDRAM Peak Bandwidth 66MB/sec 125MB/sec 200MB/sec 400MB/sec 1.

6 GB/sec MHz 66 MHz 125 MHz 200 MHz 400 MHz 800 MHz Standard Body JEDEC JEDEC JEDEC SLDRAM Consortium Rambus Availability 1995 1997 1998 1999 1999 Voltage 3.3V 3.3V 3.3V 2.5V 2.5V Source: Toshiba and Rambus The above are just the types of commonly used memories in computer there are many more types and are not to be discussed.

In SDRAM, there is PC66, PC100, and PC133. They are the internal clock speed of the memory in MHz, PC66 means the memory s maximum speed is 66MHz. The clock speed each memory capable is significant because the higher the clock speed, the faster the RAM performance. The following chart highlights the speed of different types of RAM. FPM? EDO BEDO? SDRAM Specification* -5, -6, -7 -5, -6, -7 -5, -6, -7 -10, -12, -15 Access time (ns) 50, 60, 70 50, 60, 70 52, 60, 70 50, 60, 70 Cycle time (ns) 30, 35, 40 20, 25, 30 15, 16.6, 20 10, 12, 15 Max speed (MHz) 33, 28, 25 50, 40, 33 66, 60, 50 100, 80, 66 Source: EDN, 4 Jan 1996 [Specs for standard DRAM indicate access time (ns x10) ] [Specs for SDRAM indicate cycle time (ns) ] Today s Computer Central Processing Unit (CPU) has increased their integrated memories to store the data addresses, as doing so will save time getting information needed from memory within CPU instead of from the main memory thus increase the efficiency of data processes.

The memory used in CPU is called Cache Memory, cache is a small block of high-speed memory usually SRAM? located between the CPU and main memory that is used to store frequently requested data and instructions. When the processor needs data, it will check in high-speed cache first to see if the data is there. If not, then the processor will retrieve the data from slower main memory. Caches vary in sizes; normally a CPU has 512k of Level 2 Cache (Secondary cache) some has 0k, 128k, 1Mb, or 2Mb. The more cache a CPU has, the better performance it has but more expensive.

(For example, an Intel Pentium III Xeon processor with 8-way processing will usually has 1Mb or 2Mb or L2 cache.) Below is a die map of a CPU showing the Level 2 Cache (L2) and other components. Provided by Intel Corporation. Memories play an important role in electronics that have to save critical information.

As in today s society computer is a must-have machine to help people to organize, calculate and time means money for business and companies. With today s powerful, fast CPU a fast memory will help boosting the performance and stability of computer systems and easier lives for mankind. Faster and better Memories are a stepping stone for tomorrow s technologies. Bibliography Kingston Technologies, What is Rambus? 2nd March, 1996. Online posting. 11th April, 2000.

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