Glossary of Memory and Memory Terms
Access time
1. The average time interval between a storage peripheral (usually a disk drive or semiconductor memory) receiving a request to read or write a certain location and returning the value read or completing the write.
2. A measurement of time in nanoseconds (ns) used to indicate the speed of memory. Access time is a cycle that begins the moment the CPU sends a request to memory and ends the moment the CPU receives the data it requested. Memory modules complete this process in as fast as 6ns for PC-133 MHz memory, while older modules can take up to 80ns or more.
Ambyx test system
Also called 'Ambyx Oven.' A burn-in and test system, developed by Micron, that performs burn-in and many functional tests under high-stress conditions to ensure long-term quality and reliability of our parts.
Amray
A machine that measures critical dimensions of designated areas on the die at different process levels through the use of a SEM (Scanning Electron Microscope).
Application specific processor
Highly integrated logic chip designed for specific applications to work alongside a microprocessor (e.g., a math co-processor, graphics processor, artificial intelligence processor, LAN processor, digital signal processor). These chips offload some of the specialized number crunching from the MPU.
Array
The area of the RAM that stores the bits. The array consists of rows and columns, with a cell at each intersection that can store a bit. The large rectangular section in the center of the die where the memory is stored.
ASCII
(American Standard Code for Information Interchange) A method of encoding text as binary values. The ASCII system requires nearly 256 combinations of 8-bit binary numbers to support every possible keystroke from the keyboard.
Asynchronous
A process in a multitasking system whose execution can proceed independently, "in the background.
Asynchronous Cache
Describes a type of L2 cache that is not in synch with the system clock. Asynchronous cache is slower than its synchronous counterpart, but is capable of delivering information to the CPU at a rate 10 percent faster than standard DRAM. Asynchronous cache was first used to boost memory performance in 386 systems and is still widely used today.
Auto precharge
A Synchronous DRAM feature that allows the memory chip's circuitry to close a page automatically at the end of a burst.
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B
Bandwidth
The capacity to move data on an electronic line such as a bus or a channel. In short, the amount of data moved relative to a specific time frame. It is expressed in bits, bytes, or Hertz (cycles) per second. Essentially, a measure of the capacity of data that can be moved between two points in a given period of time.
Bank
A slot or group of slots that must be populated with modules of like capacity and fulfill the data width requirement of the CPU.
Bank Schema
A method of diagramming memory configurations. The bank schema system consists of rows and columns that represent memory sockets on a system: rows indicate independent sockets and columns represent banks of sockets.
Bare board
A printed circuit board (PCB) that does not have any components on it.
BEDO
Burst EDO - A variant on EDO DRAM in which read or write cycles are batched in bursts of four. Burst
BGA
Ball Grid Array - a square package with solder balls on the underside for mounting. Use of BGA allows die package size to be reduced by allowing more surface area for attachment. Smaller packaging allows more components to be mounted on a module making greater densities available. The smaller package improves heat dissipation improving performance. See CSP and FBGA.
Binary
A method of encoding numbers as a series of bits. The binary number system, also referred to as base 2, uses combinations of only two digits - 1 and 0.
BIOS
Basic Input Output System - often referred to as CMOS, the BIOS provides an interface for a computer's hardware and software. The BIOS configuration determines how your hardware is accessed.
Bit
Short for Binary Digit, the smallest unit of data that can be processed or stored by a computer. A bit can have a value of either 1 or 0. Bits make up 'computer' language the same way letters of an alphabet make up human languages. Different combinations of different bits form 'words' and 'sentences' (actually signals) that a computer understands. Before these words and sentences can be transmitted from the CPU to memory, or vice versa, they must be broken down into 8-bit segments called bytes. Older computers were designed to handle only 8-bit data segments, while newer models have progressed to 64-bit segments. This larger bit width capacity generally means better and faster computer performance.
Block
A physical unit of information in a logical record; block size is usually expressed in bytes.
Block diagram
A circuit or system drawing concerned with major functions and interconnections between functions.
Bond pad
Square metallic pads on the die where the ball bond is attached. The bond pad is used to find acceptable eye points.
Buffered memory
This is when there is so much memory the chipset needs assistance to deal with the large loading introduced by the large amounts of memory. A buffer isolates the memory from the controller to minimize the load the chipset sees. This means adding logic, particularly drivers, to a SIMM or DIMM to increase the output current. Buffering is used to overcome signal attenuation due to capacitive loading. Modules that are "buffered" usually have small buffer chips mounted on them.
Burn-in
The process of exercising an integrated circuit at elevated voltage and temperature. This process accelerates failure normally seen as "infant mortality" in a chip. (Those chips that would fail early during actual usage will fail during burn-in. Those that pass have a life expectancy much greater than that required for normal usage.)
Burst Mode
Bursting is a rapid data-transfer technique that automatically generates a block of data (a series of consecutive addresses) every time the processor requests a single address. The assumption is that the next data-address the processor will request will be sequential to the previous one. Bursting can be applied both to read operations (from memory) and write operations (to memory).
Bus
The central communication avenue in a PCs system board. It normally consists of a set of parallel wires or signal traces that connect the CPU, the memory, all input/output devices, and peripherals and allows data to be transferred from one system component to another. Busses come in a variety of bit widths and speeds. To prevent data bottlenecks, the components attached to a bus must operate at close to the same speed as the bus.
Bus cycle
A single transaction occurring between the system memory and the CPU.
Byte
A unit of information made up of 8 bits. The byte is the fundamental unit of computer processing; almost all aspects of a computer's performance and specifications are measured in bytes or multiples of bytes such as kilobytes (~1,000 bytes) or megabytes (~1 million bytes), or gigabytes (~ 1 billion bytes)
C
Cache
A small fast area memory holding recently accessed data, designed to speed up subsequent access to the same data. Typically used between a processor and main memory.
Cache Controller
The circuit in control of the interface between the CPU, cache and DRAM (main memory).
Cache memory
Cache RAM is high-speed memory (usually SRAM) which is dedicated to storing frequently requested data. If the CPU needs data, it will check in the high-speed cache memory first before looking in the slower main memory. Cache memory may be three to five times faster than system DRAM. Most computers have two separate memory caches; L1 cache, located on the CPU, and L2 cache, located between the CPU and DRAM. L1 cache is faster than L2, and is the first place the CPU looks for its data. If data is not found in L1 cache, the search continues with the L2 cache, and then on to DRAM.
Capacitance
The property of a circuit element that allows it store an electrical charge.
Card Memory
A type of memory typically used in laptop and notebook computers. Credit card memory features a small for factor and is named for its similarity to the size of credit card.
CAS
(Column Address Select/or Strobe)--A control pin on a DRAM used to and activate a column address. The column selected on a DRAM is determined by the data present at the address pins when CAS becomes active.
CAS-RAS (CBR) (CAS before RAS)
CAS before RAS. Column Address Strobe Before Row Address Strobe. A fast refresh technique in which the DRAM keeps track of the next row it needs to refresh, thus simplifying what a system would have to do to refresh the part.
Catastrophic failure
When a device that was initially good now fails to function under any condition.
Check Bits
Extra data bits provided by a DRAM module to support ECC function. For a 4-byte bus, 7 or 8 check bits are needed to implement ECC, resulting in a total bus width of 39 or 40 bits. On an 8-byte bus, 8 additional bits are required, resulting in a bus width of 72 bits.
Checkboard
A detail test pattern designed to exercise each individual cell in the memory and find possible shorts between adjacent columns and data buses
CHMOS
Complementary High-density Metal Oxide Semiconductor.
CISC
Complex Instruction Set Computing. This design logic is usually associated with microprocessors. CISC chips use instructions, or commands, that involve several steps in one.
Clock Rate
The number of pulses emitted from a computer's clock in one second; it determines the rate at which logical or arithmetic gating is performed in a synchronous computer. An electrical current that alternates between high and low voltages. The speed of the clock is measured in Megahertz (MHz).
Clock Speed
The rate at which a computer's internal system clock operates. The clock is used to synchronize operations between the components within the clock.
CMOS
Complementary Metal Oxide Semiconductor. A process that uses both N- and P-channel devices in a complimentary fashion to achieve small geometries and low power consumption. On a PC CMOS generally refers to the BIOS information stored on a CMOS chip.
COAST
Cache On A Stick. Coast modules were used to upgrade a motherboard's L2 cache and Tag memory on some socket 7 and older motherboards.
COB
Chip On Board. A system in which semiconductor dice are mounted directly on a PC board and connected with bonded wires or solder bumps. The dice are usually mechanically protected with epoxy.
Column
Part of the memory array. A bit can be stored where a column and a row intersect.
Compact Flash Memory
A fast, postage stamp size RAM that is removable. The CF Card weighs half an ounce, with roughly one-fourth the volume and one-half the thickness of a PCMCIA Type II Card. The CF Card fits into a CF PC Card Adapter making it compatible with a standard PCMCIA Type II slot on any notebook or desktop computer. This allows the easy transfer of stored digital information from the CF Card to a computer or printer. Currently, the most readily available application for the CompactFlash Card is the digital still camera.
Controller
One of the major units in a computer that interprets and carries out the instructions in a program.
Coplanarity
With respect to semi-conductor packages, the condition of leads in a package having all elements, or all elements in a seating plane, between two parallel planes.
CPU
(Central Processing Unit)--The chip in a computer that has primary responsibility for interpreting commands and running programs. The CPU is the most vital component of a computer system. The speed of the CPU has a significant impact on overall system performance, but the CPU doesn't act alone. If slower memory is paired with a fast processor, the processor will be forced to wait for the memory to respond. When the speed mismatch is extreme, the user will see numerous memory errors and even complete system failure.
CRIMM
Continuity RIMMs are used to fill all unused RIMM sockets in a system. CRIMMs do not use any active components, and are used to continue the channel so that the signal can be properly terminated at the motherboard.
CSP
Chip Scale Package. CSP is a type of BGA in which the package is roughly the size of the die. CSP is also known as mBGA or micro-BGA.
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