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Jargon
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Index
Backup Binary Bit Byte Dialup DMZ Gigabyte Kilobyte Memory Disk Offline Storage Flash Memory Moore's Law Operating System PDA Peripherals Protocol RAID Server Blade TCP/IP Ware Binary Top
Backup Top If there is anything stored on your computer that would cost you time and/or money to replace then you should have backup copies of it. What could go wrong: the data could be corrupted, the hard disk could crash, the computer could be stolen, lightning, floods, acts of God, etc. If the disk crashes or becomes corrupt you will have to spend time reinstalling the operating system, all the different applications that you use, all the device drivers that you had to track down on the Internet to make various peripherals work. You will have to rebuild you e-mail contacts and diary. And forget about anything else. It's gone. For a long time a floppy disk was the backup medium of choice. But now it's often too small for most things. Flash Memory solves a lot of problems Bit Top A bit is a single binary digit. On its own it is not much use since it can only be used to count from zero to one. Bits are usually grouped into bytes and dealt with as a single number. 32-bit computers such as the Intel Pentium use 32 bits to address memory. 32 bits can have 4,294,967,295 or four thousand million combinations. Since each address contains a byte, a 32-bit computer can have a theoretical maximum of 4 gigabytes of data. Byte Top A byte is a group of eight Disk. It can represent numbers from zero to 255. Usefully, a byte can be used to represent a character of text including the entire upper- and lower-case alphabet, all the numbers, punctuation marks and other characters commonly used in the English language. Sometimes comupters use multiples of bytes. For example memory addresses usually use four bytes and floating-point numbers, i.e. decimal fractions, might use between four and eight bytes. Dialup Top Most home computers have a dialup modem which enables them to connect to the Internet by sending signals down an ordinary telephone line. The word modem is short for Modulator/Demodulator, which means the modem turns the digital signals into sound that can be transferred along the telephone line (modulates) and at the other end a similar modem turns the sound back into digital signals (demodulates). Modem speeds are usually rates at a number of kilobits per second, e.g. 56kbps. This often misleads people who read it as kilobytes per second. Since a byte consists of eight bits, and a modem sends information one bit at a time, it therefore takes eight times longer to send a byte as to send a bit. A 56kbps modem will therefore handle a maximum of 7,000 bytes per second. DMZ Top A DMZ, or demilitarized zone, is provided by a hardware device which is a combination of a Router and a Firewall. In its simplest form the device has three network ports. The first port is generally connected to an internal network, possibly an office. The second port is connected to a wider network, often the Internet. And the third port is connected to a server, or network of servers that must be visible to both the local network and the wider world; this is the DMZ. Computers in the DMZ can be seen by both sides but each side cannot see the other. In reality the firewall may be configured to allow traffic such as e-mail and web browsing through the DMZ. Gigabyte Top A gigabyte is over a billion bytes. Giga is a word usually used to express one thousand million or 109 in decimal. However the value in binary is equal to 230 or 1,073,741,824. Disk capacity is often expressed in gigabytes. Kilobyte Top A kilobyte is over a thousand bytes. Kilo is a word usually used to express one thousand or 103 in decimal. However the value in binary is equal to 210 or 1,024. Dialup and slower network speeds are often appear to be expressed in kilobytes, but this is misleading. See Networks. Megabyte Top A megabyte is over a million bytes. Mega is a word usually used to express one million or 106 in decimal. However the value in binary is equal to 220 or 1,048,576. Memory capacity is often expressed in megabytes. Memory Top Computers store their programs and data in memory, and the basic unit of memory is a byte. The speed and size of memory has increased according to Moore's Law, meaning that thirty-two years ago computer memory was measured in kilobytes and it has grown through megabytes to gigabytes. There are basic three types of memory. The first is solid-state memory, or the chips in the computer. This is the fastest and so the most expensive. It is limited in PCs to a maximum of 4 gigabytes and retailers generally supply up to 1 gb as standard. Whilst this may seem enough for the majority of users, it has to hold the operating system, the program and the program's data. Solid-state memory is usually volatile, meaning it loses it's contents once the power is removed. So there is a need for a more permanent store. Today's main permanent stores are hard disks. When a computer is shut down, the system writes much of its memory back to the hard disk so that it can read it back again next time the computer is booted. Hard disks are sealed cases containing a magnetic disk that rotates under a head that can read and write data to and from the disk. It works on the same principle as the tape recorder. As the tape passes the head, it can sense the alignment of magnetic particles on the tape surface. For writing the head actually sets the magnetic alignment. Instead of running in a straight line like a reel or cassette of tape, the magnetic material is arranged in circular tracks on the surface of the disk. As scientists and engineers have been able to place individual particles closer together, so the capacity of hard disks has increased. Twenty years ago a 40 megabyte disk was not uncommon. Today disks may contain a hundred gigabytes or more. As memory capacity is consumed by bigger operating systems, programs and data, the need for more disk space becomes apparent. Whilst previously we only saved documents, there are now music files, electronic pictures and even movies to contend with. One interesting point to mention is that the size of the disk quoted by the manafacturer is not available to the user. A small percentage is used by the hard disk when it is formatted. A third type of storage is known as offline storage. Data is kept offline when it is not required on a regular basis, and the user can afford the time it takes to locate and load the information. Offline media can take the form of tapes, but the capacity of CDs and DVDs means that for home and small business users, these are more useable. Initially CDs were designed for music recording but since the music was recorded digitally, and replayed by what amounts to a small computer in the player, it made sense to distribute programs and data in this way. A typical CD contains up to 650 megabytes where a DVD can hold 4.7 gigabytes; the equivalent of over seven CDs. This was all well and good, the media had to be created in factories and, once written, could never be changed. Then came devices and disks that allowed the user to write once only to the disk. It was thus a useful medium for backups and archives, where the data became an historical record. Today both CDs and DVDs can be written and erased many times, so it makes sense to save large documents, prictures, music, etc. onto these, and save space on the hard disk. Flash memory is Up to 256 megabytes of memory available today on keyring fobs for laptops, and cards the size of postage stamps for cameras and handheld PCs. These are particularly useful because they non-volative and can be transported without a power supply. In future, if Moore's Law continues to hold true, we may be able to carry every piece of information we will ever need in a matchbox. The only addition will be a screen to view it and a keyboard or mouse to control it. Moore's Law Top Gordon Moore co-founded Intel in 1968. He formulated a proposition, now known as Moore's Law, that, for the same price, computers would double their speed and memory would double its capacity, every two years. Many people misquote the interval as eighteen months. So far, the law has remained true, but there is a finite limit to how small integrated circuits can be manufactured. The law may run out of steam and cause academics, scientists and engineers to seek alternative ways of improving computer speeds. Operating System Top An operating system is the software or program that manages all the underlying computer tasks whilst applications such as word processors run on top. It is essentially the glue between the hardware and the applications, but it provides many features that can be used by the applications. Such features might include printing, modem connections, scanning, disk access, screen management, etc. The easiest distinction to illustrate the point is Microsoft Windows and Microsoft Office. Windows is the operating system, and if you install it on your computer you can't do much with it. There is a web browser (the subject of much litigation over the years) a simple editor (wordpad) and a media player - another object of litigation. If you want anything else you have to get Office which gives a word processor, spreadsheet, a presentation tool, and a database - if you buy the professional edition. The litigation, incidentally, concerns Microsoft's use of its monopoly position to destroy competition. Other companies that developed web browsers and media players were put out of business because Microsoft gave the products away for free. One counter to this artificially slanted market is Linux, see below. For all operating systems it is necessary to obtain extra software, e.g. web server, e-mail host, database, etc. In addition, thare are the applications used by individual businesses such as accounting packages, graphic design tools, payroll software, and a myriad of other things a company might want to do. They all run on top of the operating system. There are alternatives. For Macintosh users the choice is obvious, i.e. Mac software. But for PCs there are flavours of Unix or Linux. The latter has been gaining ground in recent years and features very strongly as the system of choice for web servers. The advantage of Linux is that it is, essentially, free. The baby of one Linus Torvalds, it is a system that has been created by a worldwide network of software developers who are dedicated to providing top-class, free software. These people are professionals and academics who give their time freely to make a computer world that can free itself from Microsoft's monopoly. You can download several flavours of Linux from the internet, or pay a nominal amount to get it on CD. Enterprise editions from commercial companies contain more software and offer technical support, but the underlying ethos is free. The graphical links at the bottom of this page take you to sites that offer applications including web server software, a powerful database, a scripting language, and linux; all for free and used to provide the page you are now viewing. There are other operating systems that are used on larger mini and mainframe computers, but they are outside the scope of this document. The authors of this document merely wish to point out that OpenVMS is (was) one of the best. PDA Top A Personal Digital Assistant is a handheld computer that is used to store a diary, list of contacts, notes etc. There are many to choose from, including some high-end mobile phones wich contain much of the functionality of a PDA. Peripherals Top Peripherals are any units that are external to your computer but connected to it in some way. Examples might include: scanners, printers, modems, external hard disks, digital cameras, PDAs, etc. Most of these things come with a piece of software called a device driver that is installed in the computer and allows it to communicate with the attached device. If it doesn't work and you have to track down a newer version on the Internet, then make sure you have a backup copy in case you need to re-install it. Protocol Top One dictionary definition is "A code of conduct or etiquette prescribing how those taking part should behave...". It neatly sums up how computer systems must talk to each other. Each and every protocol has a set of rules and they must be performed correctly and supplied in the correct order. The details of the protocol are immaterial to the onlooker, it is simply necessary that the computers on each side of the transaction understand and obey the protocol. RAID Top RAID stands for Redundant Array of Inexpensive Disks. This concept was introduced when hard disk drives became much cheaper than they used to be. RAID provides for increased performance and/or fault tolerance. There are several levels:
Server Top A server is a standard computer that serves a specific purpose. Is is not a standard desktop box, but sits in the corner, or in the computer room, acting as a file server, an E-mail server, or maybe a web server. The first type is used to concentrate users' files, e.g. Word documents, spreadsheets, etc., in one place. This saves users having to look after the contents of their own hard disks. The administrator doesn't have to backup every individual computer every night; just the server. An e-mail server acts as the repository for everybody's messages. Again, each PC doesn't hold any information, backups are easier, and e-mails are centralised so that people can share mailboxes, contact information, diaries, etc. A web server hosts the corporate website so that all the pages for www.mywebsite.com are held in a single place and easily managed. Servers can be configured to perform identical tasks so that if one fails others will carry on with, perhaps, a slightly slower service. Once a replacement server is plugged in, the performance returns to normal. A blade server is a PC on a single card that slots into a rack, about the size of a standard PC mounted on its side. Each card has many of the usual ports associated with a PC, memory and a hard disk. A rack might be able to hold a dozen or more blades. The ideal is that the servers are kept in the most compact form possible instead of littering the computer room with countless beige boxes and associated wires. They also save money on computer screens and keyboards because they can be managed from a single central point. Blades are usually hot-swappable, meaning that a failed server can be pulled out of the rack and a new one inserted, without affecting the others. With disk mirroring the disk on the new blade can catch up with what is on the remaining servers. Happily there is no break in service. TCP/IP Top IP stands for Internet Protocol. It is the way that computers communicate across the internet. However, IP controls has packets of data are sent from one computer to another, there is no guarantee that they will get there safely or that a long message, perhaps a file transfer or e-mail, will get there in its entirety. Transmission Control Protocol works to ensure this happens. TCP allows the computers to communicate not only the data but also what is happening. The recipient can acknowledge receipt of a packet and request the restansmission of a lost packet. Ware Top The word can ware mean An article of merchandise or manufacture; goods, commodities. Instances of usage in the computer world include the following:
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