Glossary

address bus

The connections between the CPU and memory which carry the address from/to which the CPU wishes to read or write. The number of bits of address bus determines the maximum size of memory which the processor can access. (FOLDOC, retrieved 2013-08-08.)

bit (b)

Binary digit. A bit is said to be “set” if its value is true or 1, and “reset” or “clear” if its value is false or 0. One speaks of setting and clearing bits. To toggle or “invert” a bit is to change it, either from 0 to 1 or from 1 to 0. (FOLDOC, retrieved 2013-08-05.)

byte (B)

A component in the machine data hierarchy larger than a bit and usually smaller than a word; now nearly always eight bits and the smallest addressable unit of storage. A byte typically holds one character. (FOLDOC, retrieved 2013-08-05.)

cache

A small fast memory holding recently accessed data, designed to speed up subsequent access to the same data. Most often applied to processor-memory access but also used for a local copy of data accessible over a network etc. More …. (FOLDOC, retrieved 2013-08-08.)

capacitor

An electronic device that can store electrical charge.… The basis of a dynamic RAM cell is a capacitor. (FOLDOC, retrieved 2015-01-05.)

cell

A fixed-size unit of random-access memory with a unique unsigned integer address usually numbered from zero. A cell is the minimum unit of access: all memory access is to a specified address and must fetch or store all of the bits in the cell. The number of bits in a cell is called the cell size or memory width and is usually 8 bits. Compare with byte and word.

data bus

The bus (connections between and within the CPU, memory, and peripherals) used to carry data. Other connections are the address bus and control signals. ¶The width and clock rate of the data bus determine its data rate (the number of bytes per second it can carry), which is one of the main factors determining the processing power of a computer. Most current processor designs use a 32-bit bus, meaning that 32 bits of data can be transferred at once. Some processors have an internal data bus which is wider than their external bus in order to make external connections cheaper while retaining some of the benefits in processing power of a wider bus. (FOLDOC, retrieved 2013-08-08.)

denary/decimal

The base-10 number system.

flip-flop

A circuit which produces an output value, of 0 or 1, which remains constant until a pulse from another circuit causes it to shift to the other value. In other words, the output will flip or flop between two values under the control of external stimuli (Brookshear, 2012, p. 23.)

gate

A device that produces the output of a Boolean operation when given the operation’s input values (Brookshear, 2012, p. 21.)

A low-level digital logic component. Gates perform Boolean functions (e.g. AND, NOT), store bits of data (e.g. a flip-flop), and connect and disconnect various parts of the overall circuit to control the flow of data (tri-state buffer). (FOLDOC, retrieved 2013-08-01.)

hexidecimal

The base-16 number system.

Consists of 16 unique symbols: the digits 0 to 9 and the letters A to F. Useful because it can represent every 8-bit byte as two consecutive hexadecimal digits. To convert a value from hexadecimal to binary, translate each hexadecimal digit into its 4-bit binary equivalent. Hexadecimal numbers have either an 0x prefix or an h suffix. (Webopedia, retrieved 2014-03-24.)

integrated circuit (IC or “chip”)

A microelectronic semiconductor device consisting of many interconnected transistors and other components. Digital integrated circuits can contain anything from one to millions of logic gates—inverters, AND, OR, NAND, and NOR gates, flip-flops, multiplexors, etc.—on a few square millimetres. The small size of these circuits allows high speed, low power dissipation, and reduced manufacturing cost compared with board-level integration. ¶The first integrated circuits contained only a few transistors. Small Scale Integration (SSI) brought circuits containing transistors numbered in the tens. Later, Medium Scale Integration (MSI) contained hundreds of transistors. Further development lead to Large Scale Integration (LSI) (thousands) and VLSI (hundreds of thousands and beyond). In 1986, the first one megabyte RAM was introduced which contained more than one million transistors. ¶LSI circuits began to be produced in large quantities around 1970 for computer main memories and pocket calculators. For the first time it became possible to fabricate a CPU or even an entire microprocesor on a single integrated circuit. (Abridged from FOLDOC, retrieved 2015-01-05.)

main memory

For the purpose of storing data, a computer contains a large collection of circuits (such as flip-flops), each capable of storing a single bit. This bit reservoir is known as the machine’s main memory. (Brookshear, 2012, p. 26.)

Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or discs. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disc. ¶Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes of information. (What is Memory? Webopedia, retrieved 2015-01-05.)

overflow

The problem that occurs when a computation produces a value which falls outside the range of values which can be represented (Brookshear, 2012, p. 50.)

radix

Any number that is the base of a number system or of a system of logarithms. For example, 10 is the radix of the decimal system. (Collins English Dictionary, retrieved 2013-08-01.)

RAM (Random-Access Memory)

RAM is an acronym for Random-Access Memory, a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without accessing the preceding bytes (abridged from Webopedia, retrieved 2015-01-05.)

See also: DRAM Memory Guide.

register

One of a small number of high-speed memory locations in a computer’s CPU. Registers differ from ordinary random-access memory in several respects: There are only a small number of registers (the “register set”), typically 32 in a modern processor though some, e.g. SPARC, have as many as 144. A register may be directly addressed with a few bits. In contrast, there are usually millions of words of main memory (RAM), requiring at least twenty bits to specify a memory location. Main memory locations are often specified indirectly, using an indirect addressing mode where[by] the actual memory address is held in a register. ¶Registers are fast; typically, two registers can be read and a third written—all in a single cycle. Memory is slower; a single access can require several cycles. ¶The limited size and high speed of the register set makes it one of the critical resources in most computer architectures. Register allocation, typically one phase of the back-end, controls the use of registers by a compiled program. (FOLDOC, retrieved 2013-08-05.)

semiconductor

A material, typically crystaline, which allows current to flow under certain circumstances. Common semiconductors are silicon, germanium, gallium arsenide. Semiconductors are used to make diodes, transistors and other basic "solid state" electronic components. (FOLDOC, retrieved 2015-01-05.)

A material that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber). The most common semiconductor materials are silicon and germanium. These materials are then doped to create an excess or lack of electrons. Computer chips, both for CPU and memory, are composed of semiconductor materials. Semiconductors make it possible to miniaturize electronic components, such as transistors. Not only does miniaturization mean that the components take up less space, it also means that they are faster and require less energy. (Webopedia, retrieved 2015-01-05.)

stream

An abstraction referring to any flow of data from a source (or sender, producer) to a single sink (or receiver, consumer). A stream usually flows through a channel of some kind, as opposed to packets which may be addressed and routed independently, possibly to multiple recipients. Streams usually require some mechanism for establishing a channel or a “connection” between the sender and receiver. (FOLDOC, retrieved 2013-08-01.)

A long stream of bits (Brookshear, 2012, p. 24.)

transistor

A three terminal semiconductor amplifying device, the fundamental component of most active electronic circuits, including digital electronics. The transistor was invented on 1947-12-23 at Bell Labs.… Transistors and other components are interconnected to make complex integrated circuits such as logic gates, microprocessors and memory. (FOLDOC, retrieved 2015-01-05.)

A device that acts, depending on the voltage level of the input signal, either as a wire that conducts electricity or as a resistor that blocks the flow of electricity. A transistor has no moving parts, yet it acts like a switch. It is made of a semiconductor material, usually silicon (Dale and Lewis, 2013, p. 99).

word

The number of bits that the CPU can process simultaneously. Compare with cell.

A group of bits which can be addressed, transferred, and manipulated as a single unit by the central processing unit (IBO, 2008, p. 90.)

A fundamental unit of storage in a computer. The size of a word in a particular computer architecture is one of its chief distinguishing characteristics. The size of a word is usually the same as the width of the computer’s data bus so it is possible to read or write a word in a single operation. An instruction is usually one or more words long and a word can be used to hold a whole number of characters. These days, this nearly always means a whole number of bytes (eight bits), most often 32 or 64 bits. (FOLDOC, retrieved 2015-01-11.)

References

Brookshear, J. Glenn (2012). Computer science: an overview (11th edition). Toronto: Addison-Wesley. ISBN 9780132569033.

Dale, N., and Lewis, J. (2013). Computer science illuminated (5th edition). Burlington, MA: Jones & Bartlett Learning. ISBN 9781449672843.

IBO (2008). Diploma Programme: Computer science guide (revised edition). Cardiff: International Baccalaureate Organization.

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