Select Committee on Science and Technology Second Report


APPENDIX 8: ABBREVIATIONS AND GLOSSARY

3GThird generation
ALUArithmetic logic unit
BCSBritish Computer Society
CITRISCentre for IT Research in the Interest of Society, University of California
CMOSComplementary Metal-Oxide-Semiconductor
CPUCentral processor unit
CRTCathode ray tube
CSComputer Science
bnbillion
DTIDepartment of Trade and Industry
DSPDigital Signal Processor
EPSRCEngineering and Physical Sciences Research Council
EUEuropean Union
EUVExtreme ultra-violet
FETField-effect transistor
GDPGross Domestic Product
GSMGlobal System for Mobile communications
HEFCEHigher Education Funding Council for England
ICTInformation and communication technology
IEEInstitution of Electrical Engineering
IMECInter-University Microelectronics Centre, Belgium
IPIntellectual property
IRCInterdisciplinary Research Collaboration
ISLIInstitute for System Level Integration, Livingston
ITInformation Technology
IT&CSInformation Technology and Computer Science
ITRSInternational Technology Roadmap for Semiconductors
LCDLiquid crystal display
mmmillimetre
nmnanometre
NHSNational Health Service
NPLNational Physical Laboratory
OECDOrganisation for Economic Co-operation and Development
OMIOpen Microprocessor Systems Initiative
ppage number in the accompanying volume of evidence
PCPersonal computer
PDAPersonal digital assistant
PPARCParticle Physics and Astronomy Research Council
Qquestion number in the accompanying volume of evidence
qubitquantum bit
R&DResearch and development
RAEResearch Assessment Exercise
RISCReduced instruction set computing
SETIThe Search for Extraterrestrial Intelligence project
SLISystem level integration
SoCSystem-on-Chip
UKUnited Kingdom
USUnited States of America
UVUltra-violet

Very large and very small numbers

1.  Modern computer technology involves both very large and very small numbers. To avoid long names or large numbers of decimal places, these are normally indicated by use of standard prefixes. For example, a millionth of a second is referred to as a microsecond and a millionth of a metre is a micrometre (also sometimes referred to as a micron).

2.  These prefixes cover the very large to the very small as in the following table. The difference between each step is a factor of a thousand.

Prefix
Symbol
Quantity
Number
Notation
Tera-
T
million million
1000000000000
1012
Giga-
G
thousand million
1000000000
109
Mega-
M
million
1000000
106
Kilo-
k
thousand
1000
103
  
  
one
1
  
Milli-
m
thousandth
0.001
10-3
Micro-
µ
millionth
0.000001
10-6
Nano-
n
thousand millionth
0.000000001
10-9
Pico-
p
million millionth
0.000000000001
10-12
Femto-
f
thousand million millionth
0.000000000000001
10-15


3.  It is obviously easier to say "3 gigahertz" (a measure of computer speed) than "three thousand million hertz". For calculations and some other purposes, however, it is necessary to write down the numbers. If written in full, 3 gigahertz would be 3,000,000,000 hertz. However, the conventional way of writing such a large number is 3 x 109, being three multiplied by 10 to the power 9 (10 multiplied by itself nine times) or a thousand million.

4.  Such power notation is also used to simplify very small numbers. A minus power represents one divided by the number that would be generated by that power if positive. For example, 10-9 (referred to as "10 to the minus 9") is one divided by 109 or one thousand millionth. 5 nanometres (being five thousand millionths of a metre or 0.000000005 metres) may thus be written as 5 x 10-9 metres.

Dimensions

5.  Individual elements on a modern computer chip are best measured in nanometres (nm), of which there are one thousand million to the metre, the standard metric unit of length. (The now less-used Ångström unit is one tenth of a nanometre.)

6.  To illustrate such very small distances, a ream (500 sheets) of standard paper is 50 millimetres thick. 10 sheets are thus a millimetre and a single sheet is 100 micrometres thick. A nanometre is one thousandth of a micrometre. If it were possible to make paper only one nanometre thick, it would take one hundred thousand sheets (200 reams) to equal the thickness of one sheet of ordinary paper.

7.  Computer chips are manufactured in layers, some of which are only 1.5 nm thick. Atoms in a silicon crystal are about a fifth of a nanometre apart, so such layers are only 7 or 8 atoms thick. Critical horizontal measurements can be as small as 5 nm or 25 atoms.

Speed

8.  A computer's actions are synchronised by high-frequency pulses from its clock. The standard measurement of frequency is the hertz, being one event per second. Modern PCs operate at clock rates in the gigahertz range, that is at over a thousand million (109) cycles per second. To say that a computer works at 1 gigahertz is exactly the same as saying that it completes each event in 1 nanosecond (10-9 seconds).

9.  Each step of a computer's operation is one of those events. However, delivering a program instruction (for example, retrieving data, processing it and storing the result) involves several steps. A measure of a computer's operating speed is the millions of instructions per second (MIPS) with which it can deal.

10.  Calculations involving fractions are more complicated than dealing with integers. For some applications, users need to know a computer's speed in handling floating point operations per second (FLOPS).

11.  Early computers completed each operation before turning to the next so their speed in MIPS was always less than their clock rate. Modern machines not only handle a number of instructions in parallel but also begin the next batch of instructions before the previous batch is finished. Their speed in MIPS or FLOPS can thus exceed their clock rates.

Storage capacity

12.  The basic unit of computer data is a binary bit — which will have the value of either one or zero. (What a bit represents is dictated by its context.)

13.  A block of 8 bits is called a byte. Modern computers handle "words" of 32 or 64 bits simultaneously.

14.  Computers' data storage capacity is now normally measured in megabytes and gigabytes — and even in terabytes.



 
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