Tim Thornton’s series on using PCs at sea continues in Yachting Monthly.

Don’t miss the July issue when he explains how to make cheaper calls when cruising.

Algorithm – A set of well-defined rules or operations designed to solve a particular problem reliably and efficiently

AM – Amplitude modulation. Where the carrier signals amplitude (size) changes according to the frequency of an applied signal

ANSI – American National Standards Institute

ARCS – Admiralty raster chart service. Range of electronic raster versions of UKHO paper charts

ARPA – Automated radar plotting aid

ASCII – American Standard Code for Information Interchange. System whereby numbers, letters and symbols are expressed as numbers for easy processing by computers

Bandwidth – The amount of data that can be sent through a given communications system in a given period of time

Baud – Unit of signal frequency in signals per second. Not synonymous with bits per second because signals can represent more than one bit. Baud equals bits per second only when the signal represents a single bit

Binary – Characteristic of having only two states, such as on or off. The binary number system uses only ones and zeros

Bit – Binary digit. The basic unit of all digital communications. A bit is a ‘one’ or ‘zero’ in a binary language

BPS – Bits per second. A measure of transmission speed

Bus – Data interfacing system that joins PC components together

Byte – A data unit of eight bits

Carrier Signal – A continuous waveform (usually electrical) with properties capable of being modulated or impressed with a second information-carrying signal

CCITT – Committee Consultatif Internationale de Telegraphique et Telephoni que. The International Telegraph and Telephone Consultative Committee, once part of the ITU

CD-ROM – Compact disc – read only memory

CRC – Cyclic redundancy check CRT – Cathode ray tube. Traditional ‘tube’ used for TV or computer monitor display

CW – Carrier wave

DC – Direct current

DGPS – Differential GPS. A technique to improve GPS accuracy that uses pseudo-range errors recorded at a known location to improve the measurements made by other GPS receivers within the same general geographic area, with corrections transmitted over radio

Digital – The method of representing information as numbers with discrete (non continuous) values, usually expressed as a sequence of binary digits (ones and zeros)

DMA – Direct memory access or Defense Mapping Agency (US)

DoD – Department of Defense (US)

DRAM – Dynamic random access memory

Duplex – Characteristic of data transmission. Either full or half-duplex. Full permits simultaneous two-way commuiziication. Half means only one side can talk at once

DVD – Digital versatile disk. A much higher capacity development of the CD-ROM, used for computer data storage and as a replacement for the video cassette

ECDIS – Electronic chart display and information system. A special term that refers to large ship bridge navigation systems conforming to standards laid down by the IMO

ECS – Electronic charting system. General term used to describe any computerised system capable of displaying electronic charts

EMC – Electromagnetic compatibility. The ability of electrical and electronic devices to work together without interference problems

[NC – Electronic navigational chart – A special term referring to electronic charts that conform to specific international standards for use with commercial ECDIS bridge systems

EPIRBs – Electronic Position Indicating Radio Beacons

ETSI – European Telecommunications Standards Institute. A counterpart to ANSI, facilitating integration of telecommunications standards into all of Europe and co-ordinating telecommunications policies

FAQ – Frequently asked questions.

FEC – Forward error correction. An error correction method used in data transmission

FM – Frequency modulation

FSK – Frequency shift keying modulation method

FTP – File transfer protocol. Internet service for up and downloading files efficiently

GMDSS – Global Maritime Distress and Safety System. A global standard for signalling and dealing with marine distress situations, using a combination of VHF, MF/HF radio, INMARSATA, B and C

GMT – Greenwich Mean Time

GPS – Global positioning system. A series of satellites combined with specialised devices that allow you to pinpoint exact locations anywhere on the earth, typically, Longitude and Latitude. A space-based radio positioning system which provides suitably equipped users with accurate position, velocity and time data. GPS provides this data free of direct user charge worldwide, continuously and under all weather conditions. The GPS constellation consists of 24 orbiting satellites, four equally spaced around each of six different orbital planes

GSM – Global System for Mobile Communications, or Groupe Spéciale Mobile. A pan-European cellular phone system that allows European travellers to use a single cellular phone in many different countries and have all calls billed to one account. Adopted as the preferred cellular standard in Europe, Asia and North America

HCRF – Hydrographic Chart Raster Format. The standard created by the UKHO for their ARCS raster charts, now being adopted by other hydrographic offices as well

HDOP – Horizontal dilution of precision. A measure of how much the geometry of the GPS satellites affects the position estimate (computed from the satellite range measurements) in the horizontal East/North plane

Hz – Hertz. Unit of frequency

IEEE – Institute of Electrical and Electronics Engineers. A worldwide engineering publishing and standards-making body for the electronics industry

IHO – International Hydrographic Organisation

IMO – International MaritimeOrganisation. Intergovernmental organisation with responsibility for maintaining standards of safety at sea

INMARSAT – International Maritime Satellite Organisation

ISA – Industry Standard Architecture bus. The original PC bus, still fitted to machines but largely superseded by the PCI bus.

ISDN – Integrated Services Digital Network. A high speed data line (64kbps) used as an alternative to a normal phone line, and also available over the INMARSAT B system

ISO – International Standards Organisation. Devoted to determining standards for international and national data communications

ISP – Internet service provider. A company that gives the public access to the internet

ITU – International Telecommunications Union. An organisation established by the United Nations and having as its membership virtually every government in the world

ITU-T – International Telecommunications Union Telecommunications. An international body of member countries whose task is to define recommendations and standards relating to the international telecommunications industry. Has replaced the CCITT as the worlds leading telecommunications standards organisation

kbps – Kilobits per second. A measure of transmission speed

kHz – Kilohertz. One thousand Hejtz, or cycles, per second

LES – Land earth station. This station is the interface between a communications satellite and the land based phone system

Lithium Ion (Li-Ion) battery – An efficient battery technology, supporting relatively long standby and talk time with no memory effect

LOA – Length over all

LSB – Lower side band

Mbps – Megabits per second. A million bits per second, a measure of transmission speed

MHz – Megahertz. One million Hertz, or cycles per second

Modem – A device that links computers via telephone lines and enables the transmission of data. The name comes from ‘modulate and demodulate’: a modem converts (modulates) the PC’s signals from digital to analogue for transmission over telephone lines. At the other end, another modem converts them back (demodulates) from analogue to digital

Modulation – Superimposing data on top of a ‘carrier’ signal such that when the carrier signal is removed, the original data is left

Motherboard – Part of the computer system that includes data pathways between each major system component

MS-DOS – Microsoft Disk Operating System. A text-based operating system, common in the 1980s and early 1990s. In fact, Microsoft Windows 95 and 98 both run on top of a special version of MS-DOS, but it is mostly hidden from the user

MTBF – Mean time between failure. The average time a device runs until it fails

NiCad – Nickel cadmium. A type of battery

NiMH – Nickel metal hydride. A type of battery

NMEA – National Marine Electronics Association (US)

NMEAO183 – A standard protocol deviced by the NMEA to enable instruments to communicate with each other (and also with computers)

NOAA – US National Oceanographic and Aeronautical Administration

Non-volatile (memory) see NVRAM

NVRAM – Non-volatile random access memory

OEM – Original equipment manufacturer

Opto-isolator – A device used to help eliminate electrical interference, and also to protect devices from electrical surges down data cables. It is required to be fitted on the receive side of all NMEAO1 83 interfaces.

Packet – A bundle of data, usually in binary form, organised in a specific way for transmission. Three principal elements are included in the packet: 1, control information such as destination, origin and length of packet; 2, the data to be transmitted; and 3, error-detection and correction bits

Parallel port – A port used for interfacing to printers and other devices. A number of data lines are used to send multiple items of data at once, as opposed to a serial port where the data just goes down one data line

PC Card (formerly PCMCIA card). Credit sized cards for use with laptop PCs, defined by the PCMCIA standard. The PCMCIA standards include three types, distinguished by increasing thickness: type 1: very thin memory cards, seldom used, type 2: most modems and interfaces; type 3: double thickness cards used for disk drives.

PCB – Printed circuit board

PCI – The standard bus for internal PC expansion cards, much faster than the ISA bus also installed in most machines.

PCMCIA – See PC Card

Protocol – A specific set of rules, procedures or conventions relating to format and timing of data transmission between two devices

Psion – A manufacturer of hand held computers, with their own proprietary operating system

PSTN – Public switched telephone network. Usually refers to the worldwide voice telephone network accessible to all those with telephones and access privileges. The PSTN is a gigantic maze of switching computers that can connect any two telephone points in potentially hundreds of different ways

RAM – Random access memory. Read-write volatile memory that is lost when power is discontinued; temporary storage

Raster – An image represented as a regular grid of different colour pixels. In charts, used to refer to scanned in charts

RS232 – The standard protocol used for serial ports on PCs

RS422 – A serial data standard used by Macintosh computers and also an element of the NMEA specification

SA – Selective availability. The method used by the DoD to control access to the full GPS accuracy

SCSI – Small computer systems interface. An interface used for high performance hard disks, CD-ROM drives and some other peripherals

SMS – Short message service. Enables a GSM phone to send a short text message to another GSM phone

SOLAS – Safety of life at sea

SSB – Single side band

Synchronous – Signals that are sourced from the same timing reference and have the same frequency; events that happen at the same time with respect to network timing

TCP/IP – Transmission Control Protocol/Internet Protocol. The network protocol used for the internet and for many local area computer networks

TFT – Thin film transistor. Technology used to produce flat panel computer and TV displays

UHF – Ultra high frequency

UKHO – United Kingdom Hydrographic Office

USB – Universal serial bus. A method of linking numerous external devices to a PC

USB – Upper side band

UTC – Universal Time Coordinated. This time system uses the second defined true angular rotation of the earth measured as if the earth rotated about its conventional terrestrial pole. However, UTC is adjusted only in increments of 1 second. The time zone of UTC is that of GMT

Vector – A line defined by its start point, direction and length. In terms of charts, vector charts refer to charts where the data is held in a database of points, lines, areas and symbols.

VHF – Very high frequency

Volatile (memory) – memory whose contents are lost when the power is switched off, for example the memory chips installed in PCs

WGS84 – World Geodetic System (1984). A mathematical ellipsoid designed to fit the shape of the entire earth. It is often used as a reference on a worldwide basis, while other ellipsoids are used locally to provide a better fit to the earth in a local region. GPS uses the centre of the WGS84 ellipsoid as the centre of its reference frame

This glossary appears in Using PCs on Board by Rob Buttress and Tim Thornton, Adlard Coles; £15.99