BOOT CAMP 214 (26/02/02)

ZIPPING FOR PROFIT AND PLEASURE

Over the past few weeks, in our brief introduction to essential freeware and shareware, we mentioned a utility called WinZip several times. WinZip is best known for its role in extracting or ‘decompressing’ files sent over the Internet but this program has hidden depths and it is no exaggeration to say that your PC is incomplete without it – even if you have no interest in the Internet. If you haven’t already installed it, download it now from www.winzip.com or seek out one of the many PC magazines that include it on their cover-mount discs every month.

Before we explore WinZip’s many useful features it’s worth spending a few moments looking at file compression. This is a technique, using a clever piece of software called an algorithm, that reduces the size of computer files by discarding redundant information, so they can be sent more easily over the internet, or make more efficient use of storage systems.

Essentially there are two types of compression, ‘lossy’ and ‘lossless’. Lossy compression is mostly used for picture and graphics type files, where slight reductions in fine detail or colour depth are either not noticeable or can be tolerated. Lossless compression is used on data files, documents and programs etc., where the integrity of the information has to be maintained. Lossless schemes generally work by eliminating repetitive sequences of data. For example, in a text file the word ‘and’ will occur many times, each time eating up at least 40 bits of data. In lossless compression every instance of the word is replaced with a 3-digit code that requires only 9 bits of data, representing a saving of over 75%.

Over the years there have been scores of lossless compression systems but the one you’re likely to encounter is known as ‘zipping’. Zipped files are easily to spot as they have the three-letter extension ‘zip’. Once you’ve got a decompression program like WinZip on your PC, after downloading a zip file all you have to do is double-click on the icon in Windows Explorer to open WinZip, it then asks you where you want the decompressed files to be stored. Simply choose a folder, or create a new one by typing in the name, and the files will be extracted for you to access in the normal way.

Incidentally, WinZip can handle a wide range of file compression formats, with extensions such as *.arc, *.arj, *.cab, *.gz, *.lzh, *.mim, *.tar, *.taz, *.tgz, *.uue. It is unlikely that you’ll encounter most of them however you may well come across ‘CAB’ files from time to time. CAB (short for ‘cabinet’) is a proprietary compression system used by Microsoft and is commonly used to store programs and data on CD-ROM installation discs. That’s worth knowing because occasionally you will see error messages or dialogue box asking for Windows files or drivers stored in ‘CAB’ folders and WinZip can help to find and extract them.

So far we’ve only looked at WinZip’s role, as a file extraction utility but a lot of users don’t realise that WinZip can also be used to create compressed files or ‘archives’. The obvious application is for sending large files – pictures, movies, music etc – over the Internet, but there are plenty of other uses, including overcoming the nuisance of the floppy disc’s 1.4Mb file limit. We’re always banging on about how it’s important to backup irreplaceable data on your PC but as a lot of people remind us, this can be difficult, especially on older PCs without a CD writer, tape drive, Internet connection, or any means to connect or network to other PCs.

Not only can WinZip compress large files, sometimes to a fraction of their original size, but it also has a disc ‘spanning’ facility, that can be used to store large files on a number of floppy discs. It’s an ingenious system and during the compression stage each disc is automatically numbered and tagged, so that when the files are read and decompressed on another PC, WinZip recognises the number and order of discs, so there’s very little chance of data being lost or corrupted.

Unfortunately WinZip’s compression facilities are not very well presented and can be easily overlooked, but the procedure is quite straightforward. The first step is to open WinZip and click the New icon. This opens a Windows Explorer type dialogue box that lets you choose where you want the compressed file to be stored, and to give it a name. A new dialogue box opens and this is where you select the file to be compressed, this box also contains a number of options, the most important of which are Compression, Password and Disk Spanning.

The Compression drop-down menu lets you determine the size of the file WinZip creates, and how long it takes to do it; compression speed is typically between a half and one second per megabyte of data. The actual amount of compression depends on the type of file, but to give you an idea, in its raw state a 2,500-word document created in MS Word occupies a little over 100kB of disc space. WinZip will typically reduce it to between 18 and 20Kb or around one fifth of its original size.

WinZip’s Password option is an advanced security facility, which prevents a zipped file from being opened without the correct password or PIN. The level of protection is reasonably high and password protected zip files are very difficult for a non-expert to crack without sophisticated cryptographic tools  

Disk Spanning is automatically enabled when the location or destination of a zipped file is a removable disc, usually a 3.5-inch floppy. As each disc is filled with data WinZip prompts the user to remove and label it, and load the next one. Using a combination of compression and disc spanning it is possible to archive several tens of megabytes of files without too much effort.

Next week – Obey me Windows!

JARGON FILTER

ALGORITHM

A program or piece of software that processes data in a carefully ordered sequence of steps or according to a precise set of rules

COLOUR DEPTH

The amount of data used to describe a colour, which determines the range and accuracy of colours in an image

TAPE DRIVE

Data backup systems that store huge amounts of data on magnetic tape, stored in small cassettes

TOP TIP

Google (www.google.co.uk) is quite simply the best Internet search engine and it has a number of hidden facilities. Go to http://catalogs.google.com to try out a new method of searching, which Google is testing. At the moment it covers around a dozen categories, click on one of them and you’ll be able to browse through scanned images of scores of mail-order catalogues, (click to enlarge) or go direct to the company’s home page or on-line shop. It’s an amazing resource and you can easily spend hours browsing, especially if you’re interested in hard to find or unusual electronic gadgets, food, sporting goods, fashion or health care products.