some default text...

Select Committee on Science and Technology Second Report

APPENDIX 8: ABBREVIATIONS AND GLOSSARY

3G	Third generation
ALU	Arithmetic logic unit
BCS	British Computer Society
CITRIS	Centre for IT Research in the Interest of Society, University of California
CMOS	Complementary Metal-Oxide-Semiconductor
CPU	Central processor unit
CRT	Cathode ray tube
CS	Computer Science
bn	billion
DTI	Department of Trade and Industry
DSP	Digital Signal Processor
EPSRC	Engineering and Physical Sciences Research Council
EU	European Union
EUV	Extreme ultra-violet
FET	Field-effect transistor
GDP	Gross Domestic Product
GSM	Global System for Mobile communications
HEFCE	Higher Education Funding Council for England
ICT	Information and communication technology
IEE	Institution of Electrical Engineering
IMEC	Inter-University Microelectronics Centre, Belgium
IP	Intellectual property
IRC	Interdisciplinary Research Collaboration
ISLI	Institute for System Level Integration, Livingston
IT	Information Technology
IT&CS	Information Technology and Computer Science
ITRS	International Technology Roadmap for Semiconductors
LCD	Liquid crystal display
mm	millimetre
nm	nanometre
NHS	National Health Service
NPL	National Physical Laboratory
OECD	Organisation for Economic Co-operation and Development
OMI	Open Microprocessor Systems Initiative
p	page number in the accompanying volume of evidence
PC	Personal computer
PDA	Personal digital assistant
PPARC	Particle Physics and Astronomy Research Council
Q	question number in the accompanying volume of evidence
qubit	quantum bit
R&D	Research and development
RAE	Research Assessment Exercise
RISC	Reduced instruction set computing
SETI	The Search for Extraterrestrial Intelligence project
SLI	System level integration
SoC	System-on-Chip
UK	United Kingdom
US	United States of America
UV	Ultra-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.

---