Glossary: J

This page contains glossary terms beginning with the letter J.
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Word or Term Description or Explanation
Janet Joint Academic Network - the network linking UK academic institutions (Super Janet, allowing higher speed communication and other extra facilities, is currently being tested)
(Hot) JAVA an object-orientated programming language developed by Sun Microsystems, to be used across distributed systems - it allows executable 'objects' to be sent across the Internet, rather than the more traditional text - for example, you could have a graph on your screen of some data - there could be an update to that data, which JAVA would 'transmit' to your machine, and update the graph, all without any user intervention - it is rather like hot-links within documents, hence the term 'Hot' often being applied to it - apparently Java is american slang for coffee, so you will see lots of mention of hot java and animated icons of steaming cups of coffee if you visit any of the java pages - more infomation on JAVA can be found at http://java.sun.com
Javascript an interpreted, implicitly typed language, developed by Sun Microsystems - Javascript source code is designed to be embedded as markup in HTML documents - it should not be confused with Java
Jaz Discs / Drive a 1Gb capacity drive from Iomega which is removable and acts just like a very large capacity fast floppy drive
JIT compiler see Just-in-time compiler
JPEG (1) Joint Photographic Experts Group - a body set up in the USA to produce an industry standard for still picture compression and storage - the theory is that, with an agreed file format, one company's decompression program can read the files produced by someone else's compression program
JPEG (2) Joint Photographics Expert Group - a filetype which uses lossy techniques to achieve compression developed by the group as a platform-independent file-type - JPEG is a standard filetype on Acorns fitted with RISC OS 3.6 and above and is widely used on the internet - it is one of the two main standards of file format, the other one being GIF - this is due to the fact that in the UNIX world (on which the Internet is based) and in the IBM-Compatible world, there is no dominant vector filetype
Jughead a search system for finding files in gopher sites, similar to Veronica
Just-in-time compiler traditionally, execution of a compiled language proceeds in three phases: (1) the compiler reads the source code; (2) the compiler constructs the target code; (3) the target code is executed - aJIT compiler interleaves these three processes on a call-by-need basis - typically, the source code is read from an external input
this is a concept which has come about following the success of the Java programming language - the philosophy behind Java is that it is a platform-independent language, capable of being written and compiled one one platform, with the executable code being run on any other hardware platform without modification - in order to achieve this, it is compiled to a pseudo-machine code called "bytecode", which is then interpreted by a Java Virtual Machine (JVM) - because they are interpreted, albeit at a low level, Java programs run more slowly than equivalent programs written in, say, C or C++ - one way around this is for the JVM to compile the bytecode into real machine code just before it executes it - this is called Just In Time compilation (because it happens just as it is needed, and not before)

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