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Memory terms glossary

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Title Description
Access Time The amount of time it takes to access data from a memory cell. Usually measured in nanoseconds (ns).
Antistatic A term used to describe something that prevents electrostatic discharge, such as an antistatic bag.
BIOS Basic input/output system. Often referred to as CMOS, the BIOS provides an interface for a computer's hardware and software. The BIOS determines how your hardware is accessed.
BSOD (Blue Screen of Death) A blue screen displaying a crash or error message on a Windows-based system.
Bandwidth The amount of data that can be moved between two points in a given period of time. The bandwidth of DRAM modules is measured in Megabytes per second (MB/s).
Binary A computer numbering system based on two digits: 0 and 1. All information in a computer is stored and transferred in binary.
Bit Binary digit. The smallest piece of data (a 0 or a 1) that a computer recognizes.
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.
Bus A data path in a computer used to move data. See also Memory Bus.
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, such as Kilobytes (KB) and Megabytes (MB). Don't confuse byte (capital "B") with bit (lower case "b"). Bytes are capitalized becase they represent 8 bits of information; they're the larger unit of measurement.
CMOS Complimentary Metal-Oxide Semiconductor. The CMOS is the chip on the motherboard that stores information about the system's hardware settings, such as DRAM speed, timings, and voltage. You can alter the CMOS settings from the BIOS/CMOS setup.
CPU Central Processing Unit. See Processor.
Cache A type of memory that holds recently accessed data, which is designed to speed up subsequent access to the same data. Cache is usually small and very fast memory.
Chipset A chip on a motherboard that controls the data flow between the processor and the other components of the system.
Clock rate The number of pulses emitted from a computer's clock in one second. It determines the speed at which bits of information are processed or sent. The clock rate can be adjusted to process data at faster speeds. See also Overclocking.
Controller A chip that controls how data is stored, processed, and accessed.
DDR, DDR2, DDR3 DDR stands for double data rate and is a type of memory technology. Almost all modern computers run on the newer versions of DDR (DDR2 and DDR3), which offer faster speeds and additional capacity than the original DDR. DDR-based technology is not backwards compatible, so if a system is designed to use DDR3 memory, it can only use DDR3 memory. To find out which kind of memory your system is designed for, use the free Crucial System Scanner tool on our website.
DIMM Dual inline memory module. DIMMs are memory modules for desktop systems.
DRAM Dynamic Random Access Memory - it's the memory in your computer. Memory is like a computer's workspace - it's used to run applications and perform basic computer operations. The more memory a computer has, the better it's able to perform its tasks.
Dual Channel Dual channel technology uses two identical memory controllers so that two DRAM modules can be accessed simultaneously, which decreases memory lag times between one command and the next. Dual channel technology is present on most modern systems, but in order for the technology to work, the two memory modules that are installed in a system must be identical.
ECC Error Correcting Code is a logic used on some DRAM chips to catch and correct memory errors.
Electrostatic Discharge (ESD) Ever shocked yourself when you've touched a piece of metal? That's a form of electrostatic discharge (ESD). ESD is an important concept because built up static electricity can cause damage to electronic components if you touch them before your electronic charge has been released. For this reason, we recommend wearing an antistatic wrist strap when dealing with memory and other components.
Flash Memory Flash memory is a type of storage that's commonly used in USB flash drives, digital camera flash cards, and solid state drives to retain data. Flash memory is NOT related to computer memory (DRAM).
Front Side Bus (FSB) Located within the motherboard, the front side bus is the main highway for data in your computer. It connects the processor, chipset, DRAM, and graphics controller. The front side bus is decribed in terms of its width (in bits) and its speed (in megahertz).
Gigabit An amount of memory equal to 1024 megabits (1,073,741,824 bits) of information. Abbreviated Gb. Other common DRAM units of measurement are kilobits, megabits, and terabits.
Gigabyte An amount of memory equal to 1024 megabytes (1,073,741,824 bytes) of information. Abbreviated GB. Other common DRAM units of measurement are kilobytes, megabytes, gigabytes, and terabytes. Because bytes contain 8 bits of information, gigabytes are naturally larger than gigabits.
Heat Spreaders A sheath that covers a DRAM module and helps dissipate heat. Heat spreaders are usually made of aluminum and are used on some server modules and on Crucial Ballistix performance modules.
Hertz A hertz refers to one clock cycle, or one per second. Hertz are used to measure transfer speeds in computer systems. See also Megahertz.
JEDEC Joint Electron Device Engineering Council. JEDEC is an organization that establishes industry standards for memory operation, features, and specifications.
LRDIMM Load-Reduced DIMM. Available for select DDR3 servers, LRDIMMs enable more DIMMS per channel and double the installed memory capacity of a server, allowing up to 35% greater memory bandwidth.
Latency Latency is the amount of time it takes for your system's memory to respond to a command. Generally speaking, the lower the delay (latency), the faster the device. See also Timings.
Megahertz or MHz A measurement of clock cycles in millions of cycles per second. Used to show memory speeds, ex. 1333MHz or 1600MHz. See also Hertz.
Memory Bus The bus that runs from the memory controller to the memory expansion slots on the motherboard. Memory bus speed can vary and is measured in MHz.
Memory Controller The logic chip used to handle the data flow going to/from the memory. It can reside in the main chipset or in the CPU.
Module A module is the actual memory component - it's what you take out of the packaging and install in your system. When you purchase a memory upgrade, it will come in the form of a memory module. DIMMs (desktop memory modules) and SODIMMs (laptop memory modules) are the most common types of memory modules.
Motherboard The main printed circuit board in a computer that carries the system buses. It is equipped with sockets to which all processors, memory modules, plug-in cards, daughterboards, or peripheral devices are connected.
Notch Notches are cut outs that are located on the bottom of a memory module. Each memory type (SDRAM, DDR, DDR2, and DDR3) has a unique notch location for DIMMs and SODIMMs in order to prevent the wrong type of memory from being installed in the system. Notches also help ensure that the memory module is installed correctly.
OS The OS is the operating system that your computer runs on, such as a Windows or Mac OS. Windows XP and Windows 7 are examples of different operating systems.
Overclocking Running a chip at a higher clock speed than it was specified for. Oftentimes chips are capable of running faster than a manufacturer specifies, and thus can be safely overclocked. To overclock a chip, set it to either a higher bus speed, a higher multiplier, a higher voltage rate, or any combination thereof.
Printed Circuit Board (PCB) When looking at a memory module, the PCB is the green circuit board that the black DRAM chips sit on. PCBs contain layers of circuitry that connect the various memory components to the system.
Processor The Processor, or CPU, is the heart of the computer. It is responsible for carrying out all the processing of information.
RAM Random Access Memory. Data is typically stored in RAM for use by the process or while the computer is operating. RAM is considered random access because the location of the stored information does not affect the access speed. The more RAM that's available, the more applications you can have running simultaneously without slowing your system down. RAM is provided by Crucial in the form of DRAM modules.
Rambus (or RDRAM) Rambus is an alternative type of memory used in some older systems. Rambus technology uses a narrow 16-bit bus (Rambus channel) to transmit data at high speeds of up to 800MHz.
Registered Memory (RDIMMs) Server memory
SDRAM Synchronous Dynamic Random Access Memory. This memory type was the first to transfer data in synchronisation with the memory bus. It's actual name is SDR SDRAM (single data rate SDRAM), but it's usually referred to as SDRAM.
SODIMM Small Outline DIMM. Measuring at just half the length of a standard DIMM, SODIMMs are memory modules used in laptops.
SPD Serial Presence Detect is a memory feature that stores information about the module on the module's EEPROM chip. The BIOS then uses this information at startup to establish the specifications of the memory module.
Speed The speed of DRAM is measured in MHz and bandwidth. Often both will be shown in the form of DDR3-1333 PC3-10600 where the 1333 refers to the MHz speed and the 10600 the bandwidth in MB/s.
Timings Timings refer to the latency of a given memory module. Standard memory will only list the CAS Latency (CL) timing, e.g. CL=8. Performance modules such as Ballistix list CL, tRCD, tRP and tRAS in the form of four numbers seperated by dashes, e.g. 8-8-8-24. Taken together, these four numbers represent a module's timings (like latency, the lower the number, the better the performance).
Tri-Channel An extension of Dual Channel technology that can be found in some DDR3 systems. Tri-channel uses three identical memory modules for interleaving, allowing for fewer lags in memory performance.
Unbuffered Memory (UDIMMs) Standard memory used in PCs, laptops and Macs.
Virtual Memory Virtual memory is when your system borrows some of the hard drive's memory when all of its RAM is in use.
XMP Extreme Memory Profile. This is an Intel standard for providing faster timings over the standard JEDEC SPD. Memory that supports XMP can be easily overclocked by enabling XMP in the CMOS/BIOS setup.

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