WHAT IS MEMORY?

HOW MEMORY WORKS?

WHAT TO CONSIDER WHEN BUYING MEMORY?

WHAT KIND OF MEMORY IS COMPATIBLE WITH MY SYSTEM?

HOW MUCH?

HOW MANY SOCKETS DO I HAVE OPEN?

WHICH MEMORY TYPE?

GLOSSARY

MEMORY BASICS

What is memory?

"Memory" or RAM (Random Access Memory), as it is generally referred to, holds temporary instructions and data needed to complete tasks by the computer. This enables the computer's CPU (Central Processing Unit), to access instructions and data stored in memory very quickly.

When the CPU loads a program - such as a word processing- into memory, it allows the application program to work as quickly and efficiently as possible. In practical terms, having the program loaded into memory means that you can get work done more quickly with less time spent waiting for the computer to perform tasks then what it would take if the program was to be accessed from the hard-disk

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How memory works?

Similar to a microprocessor, a memory chip is an integrated circuit (IC) made of millions of transistors and capacitors. In the most common form of computer memory, dynamic random access memory (DRAM), a transistor and a capacitor are paired to create a memory cell, which represents a single bit of data. The capacitor holds the bit of information -- a 0 or a 1. The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.

A capacitor stores electrons. To store a 1 in the memory cell, the capacitor is filled with electrons. To store a 0, it is emptied. The problem with the capacitor is that it has a leak. In a matter of a few milliseconds a full capacitor becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the memory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second.

This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.

Memory cells are etched onto a silicon wafer in an array of columns and rows . The intersection of a row and column constitutes the address of the memory cell.

DRAM works by sending a charge through the appropriate column (CAS) to activate the transistor at each bit in the column. When writing, the row lines contain the state the capacitor should take on. When reading, the sense-amplifier determines the level of charge in the capacitor. If it is more than 50 percent, it reads it as a 1; otherwise it reads it as a 0. The counter tracks the refresh sequence based on which rows have been accessed in what order. The length of time necessary to do all this is so short that it is expressed in nanoseconds (billionths of a second). A memory chip rating of 70ns means that it takes 70 nanoseconds to completely read and recharge each cell.

MEMORY - PROCESSOR INTERACTION:

The CPU is often referred to as the brain of the computer where all the actual computing is done.
The chipset supports the CPU. It usually contains several "controllers" which govern how information travels between the processor and other components in the system. Systems may have more than one chipset.
The information flow between memory and the CPU is controlled by the Memory Controller, which itself may be a part of the chipset.

A bus architecture (or bus) is a data path in a computer, consisting of various parallel wires to which the CPU, memory, and all input/output devices are connected. The design of the bus determines how much and how fast data can move across the motherboard. There are several different kinds of busses in a system, depending on what speeds are required for those particular components. The memory bus runs from the memory controller to the computer's memory sockets. Newer systems have a memory bus architecture in which a frontside bus (FSB) runs from the CPU to main memory and a backside bus (BSB) which runs from the memory controller to L2 cache. Chipsets based on AMD's processors do not give much importance to FSB while calculating speed of the memory as these processors have inbuilt memory controller.

MEMORY SPEED

When the CPU needs information from memory, it sends out a request that is managed by the memory controller. The memory controller sends the request to memory and reports to the CPU when the information will be available for it to read. This entire cycle - from CPU to memory controller to memory and back to the CPU - can vary in length according to memory speed as well as other factors, such as bus speed.

Memory speed is sometimes measured in Megahertz (MHz), or in terms of access time - the actual time required to deliver data - measured in nanoseconds (ns). Whether measured in Megahertz or nanoseconds, memory speed indicates how quickly the memory module itself can deliver on a request once that request is received.

MEGAHERTZ (MHZ)

Beginning with Synchronous DRAM technology, memory chips had the ability to synchronize themselves with the computer's system clock, making it easier to measure speed in megahertz, or millions of cycles per second. Because this is the same way speed is measured in the rest of the system, it makes it easier to compare the speeds of different components and synchronize their functions.

SYSTEM CLOCK

A computer's system clock resides on the motherboard. It sends out a signal to all other computer components in rhythm, typically drawn as a square wave, like this:

Each wave in this signal measures one clock cycle. If a system clock runs at 100MHz, that means there are 100 million clock cycles in one second. Every action in the computer is timed by these clock cycles, and every action takes a certain number of clock cycles to perform. When processing a memory request, for example, the memory controller can report to the processor that the data requested will arrive in ten clock cycles.

It's possible for the CPU and other devices to run faster or slower than the system clock. Components of different speeds simply require a multiplication or division factor to synchronize them. For example, when a 100MHz system clock interacts with a 500MHz CPU, each device understands that every system clock cycle is equal to five clock cycles on the CPU; they use a factor of five to synchronize their actions.

Many people assume that the speed of the processor is the speed of the computer. But most of the time, the system bus and other components run at different speeds.

Error Checking

Most memory available today is highly reliable. Most systems simply have the memory controller check for errors at start-up and rely on that. Memory chips with built-in error-checking typically use a method known as parity to check for errors. Parity chips have an extra bit for every 8 bits of data. The way parity works is simple. Let's look at even parity first.

When the 8 bits in a byte receive data, the chip adds up the total number of 1s. If the total number of 1s is odd, the parity bit is set to 1. If the total is even, the parity bit is set to 0. When the data is read back out of the bits, the total is added up again and compared to the parity bit. If the total is odd and the parity bit is 1, then the data is assumed to be valid and is sent to the CPU. But if the total is odd and the parity bit is 0, the chip knows that there is an error somewhere in the 8 bits and dumps the data. Odd parity works the same way, but the parity bit is set to 1 when the total number of 1s in the byte are even.

The problem with parity is that it discovers errors but does nothing to correct them. If a byte of data does not match its parity bit, then the data are discarded and the system tries again. Computers in critical positions need a higher level of fault tolerance. High-end servers often have a form of error-checking known as error-correction code (ECC). Like parity, ECC uses additional bits to monitor the data in each byte. The difference is that ECC uses several bits for error checking -- how many depends on the width of the bus -- instead of one. ECC memory uses a special algorithm not only to detect single bit errors, but actually correct them as well. ECC memory will also detect instances when more than one bit of data in a byte fails. Such failures are very rare, and they are not correctable, even with ECC.

The majority of computers sold today use nonparity memory chips. These chips do not provide any type of built-in error checking, but instead rely on the memory controller for error detection.

Different kinds of memory :

It's important to note that making a choice about a computer system - and its memory features - will affect the experience and satisfaction you derive from the system. Here we tell you about memory so that you can get more out of the system you're purchasing or upgrading.

MODULE FORM FACTORS

The easiest way to categorize memory is by form factor. The form factor of any memory module describes its size and pin configuration. Most computer systems have memory sockets that can accept only one form factor. Some computer systems are designed with more than one type of memory socket, allowing a choice between two or more form factors. Such designs are usually a result of transitional periods in the industry when it's not clear which form factors will gain predominance or be more available.

Memory chips are normally only available as part of a card called a module. You've probably seen memory listed as 8x32 or 4x16. These numbers represent the number of the chips multiplied by the capacity of each individual chip, which is measured in megabits (Mb), or one million bits. Take the result and divide it by eight to get the number of megabytes on that module. For example, 4x32 means that the module has four 32-megabit chips. Multiply 4 by 32 and you get 128 megabits. Since we know that a byte has 8 bits, we need to divide our result of 128 by 8. Our result is 16 megabytes!

SIMMS:

The type of board and connector used for RAM in desktop computers has evolved over the past few years. The first types were proprietary, meaning that different computer manufacturers developed memory boards that would only work with their specific systems. Then came SIMM, which stands for single in-line memory module. This memory board used a 30-pin connector and was about 3.5 x .75 inches in size (about 9 x 2 cm). In most computers, you had to install SIMMs in pairs of equal capacity and speed. This is because the width of the bus is more than a single SIMM. For example, you would install two 8-megabyte (MB) SIMMs to get 16 megabytes total RAM. Each SIMM could send 8 bits of data at one time, while the system bus could handle 16 bits at a time. Later SIMM boards, slightly larger at 4.25 x 1 inch (about 11 x 2.5 cm), used a 72-pin connector for increased bandwidth and allowed for up to 256 MB of RAM.

Above: SIMM

DIMMS
As processors grew in speed and bandwidth capability, the industry adopted a new standard in dual in-line memory module (DIMM). With a whopping 168-pin or 184-pin connector and a size of 5.4 x 1 inch (about 14 x 2.5 cm), DIMMs range in capacity from 8 MB to 1 GB per module and can be installed singly instead of in pairs. Most PC memory modules and the modules for the Mac G5 systems operate at 2.5 volts, while older Mac G4 systems typically use 3.3 volts.

Above: DIMM

SO DIMMs
Many brands of notebook computers use proprietary memory modules, but several manufacturers use RAM based on the small outline dual in-line memory module (SODIMM) configuration. SODIMM cards are small, about 2 x 1 inch (5 x 2.5 cm), and have 144 or 200 pins. Capacity ranges from 16 MB to 1 GB per module. To conserve space, the Apple iMac desktop computer uses SODIMMs instead of the traditional DIMMs. Sub-notebook computers use even smaller DIMMs, known as MicroDIMMs, which have either 144 pins or 172 pins.


Above: SODIMM


MAJOR MEMORY TECHNOLOGIES:

SYNCHRONOUS DRAM (SDRAM)

In late 1996, SDRAM began to appear in systems. Unlike previous technologies, SDRAM is designed to synchronize itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be ready, so the CPU no longer has to wait between memory accesses. SDRAM chips also take advantage of interleaving and burst mode functions, which make memory retrieval even faster. SDRAM modules come in several different speeds so as to synchronize to the clock speeds of the systems they'll be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM runs at 100MHz, PC133 SDRAM runs at 133MHz, and so on. Faster SDRAM speeds such as 200MHz and 266MHz are currently in development.

DOUBLE DATA RATE SYNCHRONOUS DRAM (DDR SDRAM)

DDR SDRAM, is a next-generation SDRAM technology. It allows the memory chip to perform transactions on both the rising and falling edges of the clock cycle. For example, with DDR SDRAM, a 100 or 133MHz memory bus clock rate yields an effective data rate of 200MHz or 266MHz.

DOUBLE DATA RATE 2 SYNCHRONOUS DRAM (DDR2 SDRAM)

DDR2 is the second generation of Double Data Rate (DDR) SDRAM memory. It is an evolution of DDR memory technology that delivers higher speeds (up to 800 MHz), lower power consumption and heat dissipation. It is an ideal memory solution for bandwidth hungry systems and the lower power consumption is a perfect match for today's mobile users.

DIRECT RAMBUS

Direct Rambus is a DRAM architecture and interface standard that challenges traditional main memory designs. Direct Rambus technology is extraordinarily fast compared to older memory technologies. It transfers data at speeds up to 800MHz over a narrow 16-bit bus called a Direct Rambus Channel. This high-speed clock rate is possible due to a feature called "double clocked," which allows operations to occur on both the rising and falling edges of the clock cycle. Also, each memory device on an RDRAM module provides up to 1.6 gigabytes per second of bandwidth - twice the bandwidth available with current 100MHz SDRAM.

In addition to chip technologies designed for use in main memory, there are also specialty memory technologies that have been developed for video applications.

OTHER SPECIFICATIONS

In addition to form factors, memory technologies, and error checking methods, there are several other specifications important to understanding and selecting memory products.

SPEED

The speed of memory components and modules is one of the most important factors in optimizing a memory configuration. In fact, all computer systems specify a memory component speed. Ensuring memory compatibility requires conforming to this specification. This section covers three measurements of memory component and module speed: access time, megahertz, and bytes per second.

ACCESS TIME

Prior to SDRAM, memory speed was expressed by access time, measured in nanoseconds (ns). A memory module's access time indicates the amount of time it takes the module to deliver on a data request. So, smaller numbers indicate faster access times. Typical speeds were 80ns, 70ns, and 60ns. Very often, you can identify the speed of a module by the part number on the chip: such part numbers end in "-6" for 60ns, "-7" for 70ns, and so on.

In most cases you can conform to a computer system's memory specification with a module rated at the required speed or faster. For example, if your system requires 70ns memory, you can use both 70ns and 60ns memory without a problem. However, some older systems check the module ID for the rated speed at system-boot up, and will only boot up if they recognize the exact speed they are looking for. If the system has an 80ns speed specification, for example, it won't accept anything different than 80ns, even if it is faster. In many cases, modules could still be built for these systems with faster memory chips on them, but the ID on the module would be set at the slower speed to insure compatibility with the system. This is why you can't always be sure of the rated speed on a module by looking at the speed markings on the memory chips.

MEGAHERTZ

Beginning with the development of SDRAM technology, memory module speed has been measured in megahertz (MHz). Speed markings on the memory chips them-selves are typically still in nanoseconds. This can be confusing, especially since these nanosecond markings no longer measure access time, but instead measure the number of nanoseconds between clock cycles. For SDRAM chips with speeds of 66MHz, 100MHz, and 133MHz, for example, the corresponding marking on the chips are -15, -10, and -8, respectively.

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WHAT TO CONSIDER WHEN BUYING MEMORY?

The most important thing to ensure when buying memory is compatibility with your system. In addition, you'll need to decide how much memory you need and beyond that lie considerations of price, quality, availability, service, and warranty.

A. COMPATIBILITY

Compatibility of memory components with your computer system is arguably the most important factor to consider when upgrading memory.

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WHAT KIND OF MEMORY IS COMPATIBLE WITH MY SYSTEM?

The easiest way to determine what type of memory goes with your system is to consult with your system/Motherboard documentation. If you need further assistance, consult a memory configurator available from many sources, like brand-name memory companies which offer such a tool to help you find the right memory configuration for your system.
If you can't find your system in the memory configuration programs, you can still find out what kind of memory you need by consulting the manual that came with your system/motherboard. In most cases, the manual will provide basic specifications such as the speed and technology of the memory you need. This information is usually enough to choose a module by specification. If you don't feel you have enough information, you can call your system manufacturer.

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B. HOW MUCH?

Amount of Memory that should/can be added depends on following two factors:

1. APPLICATION:
It's been said that you can never have enough money, and the same holds true for RAM, especially if you do a lot of graphics-intensive work or gaming. Next to the CPU itself, RAM is the most important factor in computer performance. If you don't have enough, adding RAM can make more of a difference than getting a new CPU!
If your system responds slowly or accesses the hard drive constantly, then you need to add more RAM. If you are running Windows XP, Microsoft recommends 128MB as the minimum RAM requirement. At 64MB, you may experience frequent application problems. For optimal performance with standard desktop applications, 256MB is recommended. If you are running Windows 95/98, you need a bare minimum of 32 MB, and your computer will work much better with 64 MB. Windows NT/2000 needs at least 64 MB, and it will take everything you can throw at it, so you'll probably want 128 MB or more.
Linux works happily on a system with only 4 MB of RAM. If you plan to add X-Windows or do much serious work, however, you'll probably want 64 MB. Mac OS X systems should have a minimum of 128 MB, or for optimal performance, 512 MB.

Our Suggestion would be follows:

Where: Beginner: User who use computer for very basic purpose like word processing,
internet etc.

Casual User: User who uses computer for office applications, internet combined with occasional gaming, photo-audio-video editing etc.

Hardcore User: User who uses computer extensively for gaming, audio-video editing, intensive graphical editing etc.

Note: If the computer is to be used as a server or for server applications then we recommend to go for memory sizes for Hardcore Users.

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C. HOW MANY SOCKETS DO I HAVE OPEN?

You may or may not have an idea what the inside of your computer looks like and how memory is configured. You may have opened up your computer when you bought it to see the configuration inside, or you may have looked at a configuration diagram in your user's manual. Even if you have no idea of the memory configuration of your system, you can use 's memory configuration tools to find out. For each system, the configuration includes a diagram, called a bank schema, which indicates how the memory sockets are arranged in your system and what the basic configuration rules are. Use a bank schema diagram to determine the number of sockets in your system and how to fill them. This schema generally accompanies motherboard manual (if you have an assembled computer).

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D. WHICH MEMORY TYPE?

The type of memory you require is generally governed by the type of motherboard/chipset you have on your system. For example: computers with Intel 810 chipset supports SDRAMs only while Intel 845 chipset supports DDRs and Intel 915 chipset supports DDR2 type RAMs. We suggest you use tools like Everest Home Edition to find out the type of chipset your system has. This tool is free of cost and can be downloaded from www.lavalys.com/....

Some of the common chipsets and the corresponding type of compatible memory has been listed below for quick reference. We recommend you to check the chipset manufacturer's website for complete compatibility solution.

E. MEMORY QUALITY

Here are some important factors to keep in mind when assessing the quality of a brand of memory:

F. DESIGN

Designers of memory modules can follow strict specifications or take short cuts to save money on components. In general, manufacturers who do in-house design have more control over the quality of the module than those who farm this work out.

G. COMPONENTS

The quality of the DRAM chips, PC boards, and other components used on the module are critical to the overall quality of the module. Premium memory chips can cost up to 30% more than low-grade chips and high-quality PC boards cost about 50% more than lower quality alternatives.

H. ASSEMBLY

Many factors in module assembly can affect the overall quality of the module. In addition to proper handling of components, solder quality affects how reliably information can travel from the chip to the module and back. The temperature and humidity in the assembly and storage areas must be regulated to prevent warping, expansion, and contraction of components during assembly.

I. PROPER HANDLING

Electro-Static Discharge (ESD) is one of the most common causes of damage to a memory module. ESD damage can result from excessive and inappropriate handling. Memory modules should only be handled by workers who are properly "grounded" and modules should be properly packaged to protect against ESD during shipping.

J. TESTING

The more thoroughly memory has been tested before it is shipped, the less chance of problems during operation. In addition to standard production tests to ensure that the modules have been built correctly, memory can be tested for compatibility in the systems in which it will be used. The DRAM core can be tested for chip reliability, and modules can be tested "at speed" to make sure they will work in high-use situations. Some companies perform testing at all levels, and some do less testing.

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Glossary:

Access Time
The average time (in nanoseconds) for RAM to complete one access. Access Time is composed of address setup time and latency (the time it takes to initiate a Request for data and prepare access).

Backside Bus
(BSB) - The data path that runs between the CPU and L2 cache.

Bandwidth
The amount of data moved on electronic lines, such as a bus, per second. bandwidth is usually measured in bits per second, bytes per second, or cycles per Second (Hertz).

Bank Schema
A method of diagramming memory configurations. The bank schema consists of rows and/or columns that represent memory sockets on a computer board. Rows indicate independent sockets; columns represent banks.

Base Rambus
The first generation of Rambus technology, first shipped in 1995.

Binary
A numbering system that uses combinations of 0 and 1 to represent data. Also known as Base 2.

Bit
The smallest unit of information a computer processes. A bit is 1 or 0.

Buffer
A holding area for data shared by devices that operate at different speeds or have different priorities. A buffer allows a device to operate without the delays that other devices impose.

Buffered Memory
A memory module that contains buffers. Buffers re-drive the signals through the memory chips and allow the module to include more memory chips. Buffered and unbuffered memory cannot be mixed. The design of the computer memory controller dictates whether memory must be buffered or unbuffered.

Bus
A data path in a computer, consisting of various parallel wires to which the CPU, memory, and all input/output devices are connected.

Bus Cycle
A single transaction between main memory and the CPU.

Byte
Eight bits of information. The byte is the fundamental unit of computer processing; almost all specifications and measures of computer performance are in bytes or multiples thereof. See kilobytes and megabytes.

Cache Memory
A small amount (normally less than 1MB) of high-speed memory residing on or close to the CPU. Cache memory supplies the processor with the most frequently requested data and instructions. Level 1 cache (primary cache) is the cache closest to the processor. Level 2 cache (secondary cache) is the cache second closest to the processor and is usually on the motherboard.

CAS
(Column Address Strobe) - A memory chip signal that latches the column address of a particular location in a row-column matrix.

CAS Latency
The ratio between column access time and clock cycle time. CAS Latency 2 (CL2) offers a slight performance increase over CAS Latency 3 (CL3).

Chipset
Microchips that support the CPU. The chipset usually contains several controllers that govern how information travels between the processor and other components.

CPU
(Central Processing Unit) - The computer chip that has primary responsibility for interpreting commands and running programs. The CPU is also known as the processor or microprocessor.

DDR SDRAM
(Double Data Rate Synchronous Dynamic Random-Access Memory) - The latest generation of SDRAM technology. Data is read on both the rising and the falling edge of the computer clock, thereby delivering twice the bandwidth of standard SDRAM. With DDR SDRAM, memory speed doubles without increasing the clock frequency.

DIMM
(Dual In-line Memory Module) - A printed circuit board with gold contacts and memory devices. A DIMM is similar to a SIMM, but with this primary difference: unlike the metal leads on either side of a SIMM, which are "tied together" electrically, the leads on either side of a DIMM are electrically independent.

Direct Rambus
Rambus technology's third generation, which offers a completely new DRAM architecture for high-performance PCs. Data transfers at speeds up to 800MHz over a narrow 16-bit channel, compared to current SDRAM, which operates at 100MHz on a wide 64-bit bus.

DRAM
(Dynamic Random-Access Memory) - The most common form of RAM. DRAM can hold data for only a short time. To retain data, DRAM must be refreshed periodically. If the cell is not refreshed, the data will disappear.

Dual-Banked
A memory module having two banks.

Dual Channel
Based on the dual channel system board designs, memory modules are installed on two separate channels, each with it's own access route to the memory controller. The dual memory channel design doubles the peak bandwidth of single memory channels. Best results occur when a matched-pair memory kit is used ensuring that the modules are identical.

ECC
(Error Correction Code) - A method of checking the integrity of data in DRAM. ECC provides more elaborate error detection than parity; ECC can detect multiple-bit errors and can locate and correct single-bit errors.

Even Parity
A type of data integrity checking whereby the parity bit checks for an even number of 1s.

Form Factor
The size, configuration, and other specifications used to describe hardware. Examples of memory form factors are: SIMM, DIMM, RIMM, 30-pin, 72-pin, and 168-pin.

Frontside Bus
(FSB) - The data path that runs between the CPU and main memory (RAM).

Gigabit
Approximately 1 billion bits, or exactly 1 bit x 1,0243 (1,073,741,824) bits.

Gigabyte
Approximately 1 billion bytes, or exactly 1 byte x 1,0243 (1,073,741,824) bytes.

Heat Spreader
A sheath, usually aluminum, that covers an electronic device and dissipates heat.

Heat Sink
A component, typically zinc alloy, that dissipates heat. CPUs require heat sinks.

IC
(Integrated Circuit) - An electronic circuit on a semiconductor chip. The circuit includes components and connectors. A semiconductor chip is usually molded in a plastic or ceramic case and has external connector pins.

Kilobit
Approximately one thousand bits, or exactly 1 bit x 210 (1,024) bits.

Kilobyte
Approximately one thousand bytes, or exactly 1 byte x 210 (1,024) bytes.

Level 1 Cache
(L1) - Also known as primary cache, L1 Cache is a small amount of high-speed memory that resides on or very close to the processor. L1 Cache supplies the processor with the most frequently requested data and instructions.

Level 2 Cache
(L2) - Also known as secondary cache, L2 Cache is a small amount of high-speed memory close to the CPU and usually on the motherboard. L2 Cache supplies the processor with the most frequently requested data and instructions. Depending on the motherboard, Level 2 cache may be upgraded.

Logic Board
See Motherboard.

Megabit
Approximately one million bits, or exactly 1 bit x 1,0242 (1,048,576) bits.

Megabyte
The most common term used to denote the capacity of a memory module. One megabyte equals approximately one million bytes, or exactly 1 byte x 1,0242 (1,048,576) bytes.

Memory
A computer's random-access memory. Memory temporarily holds data and instructions for the CPU. See RAM.

Memory Bank
A logical unit of memory in a computer, the size of which the CPU determines. For example, a 32-bit CPU requires memory banks that provide 32 bits of information at a time. A bank can consist of one or more memory modules.

Memory Bus
The bus that runs from the CPU to the memory expansion slots.

Memory Controller Hub
(MCH) - The interface between the processor, Accelerated Graphics Port, and RDRAM on motherboards that use Intel's 820 or 840 chipsets.

Memory Translator Hub
(MTH) - The interface that allows SDRAM memory to be supported on a Direct Rambus Channel for motherboards using Intel's 820 chipset.

Motherboard
Also known as the logic board, main board, or computer board, the motherboard is the computer's main board and in most cases holds all CPU, memory, and I/O functions or has expansion slots for them.

Nanosecond
(ns) - One billionth of a second. Memory data access times are in nanoseconds. For example, memory access times for typical 30- and 72-pin SIMM modules range from 60 to 100 nanoseconds.

Odd Parity
Data integrity checking in which the parity bit checks for an odd number of 1s.

Parity
Data integrity checking that adds a single bit to each byte of data. The parity bit is used to detect errors in the other 8 bits.

Proprietary Memory
Memory custom designed for a specific computer.

RAM
(Random-Access Memory) - A memory cell configuration that holds data for processing by a central processing unit (CPU). Random means the CPU can retrieve data from any address within RAM. See also Memory.

Rambus
(1) Rambus, Inc. develops and licenses high-performance memory logic and circuit design technology and provides licensees with product design, layout, and testing information. (2) Direct Rambus is a high-speed memory technology that uses a narrow 16-bit bus (Rambus channel) to transmit data at speeds up to 800MHz. See Rambus Channel.

Rambus Channel
The data path of Rambus systems. Because of the narrow data width (two bytes), Rambus modules transfer data at up to 800MHz.

RAS
A memory chip signal that latches the row address of a particular location in a row-column matrix.

Refresh
Refreshing maintains data stored in DRAM. The process of refreshing electrical cells on a DRAM component is similar to recharging batteries. Different DRAM components require different refresh methods.

Refresh Rate
The number of DRAM component rows that must be refreshed. Three common refresh rates are 2K, 4K and 8K.

Registered Memory
SDRAM memory that contains registers directly on the module. The registers re-drive the signals through the memory chips and allow the module to be built with more memory chips. Registered and unbuffered memory cannot be mixed. The design of the computer memory controller dictates which type of memory the computer requires.

RIMMT
The trademarked name for a Direct Rambus memory module. A RIMMT conforms to the DIMM form factor and transfers data 16 bits at a time.

RIMM Connector
A Direct Rambus memory socket.

SDRAM
(Synchronous DRAM) - A DRAM technology that 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 in synch. Synchronous DRAM saves time in executing commands and transmitting data, thereby increasing the overall performance of the computer. SDRAM allows the CPU to access memory approximately 25 percent faster than EDO memory.

Self-Refresh
A memory technology that enables DRAM to refresh on its own and independent of the CPU or external refresh circuitry. Self-Refresh technology is built into the DRAM chip itself and reduces power consumption dramatically. Notebook and laptop computers use this technology.

SIMM
(Single In-line Memory Module) - A printed circuit board having memory devices and gold or tin/lead contacts. A SIMM plugs into a computer memory expansion socket. SIMMs offer two main advantages: ease of installation and minimal consumption of board surface. A vertically mounted SIMM requires only a fraction of the space required by a horizontally mounted DRAM. A SIMM may have as few as 30 or as many as 200 pins. On a SIMM, the metal leads on either side of the board are electrically tied together.

SIMM Socket
A motherboard component that holds a single SIMM.

Single-Banked
A module that has only one bank or row.

SO DIMM
(Small-Outline Dual In-line Memory Module) - An enhanced version of a standard DIMM. A 72-pin small-outline DIMM is about half the length of a 72-pin SIMM. 144-pin and 200-pin modules are the most common SO DIMMs today.

SO-RIMMT
The trademarked name for a Direct Rambus memory module in notebook computers. SO-RIMMTs provide memory bandwidth comparable to desktop memory configurations.

Storage
A data-holding device, such as a hard disk or CD-ROM.

Unbuffered Memory
Memory that does not contain buffers or registers located on the module. Instead, these devices are located on the motherboard

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