Fullscreen HTML5Med Res (??MB)HTML4

COMPUTER BITS By JENNIFER BONNITCHA Mass storage devices than Ben Hur What do you do when even the biggest hard disc drive is not enough? You go to a mass storage device such as a CD-ROM or WORM drive. These can store huge amounts of data but they don't replace hard discs. Remember the celebrations in 1988 - Australia's Bicentennial of European settlement? One can only wonder what the computer world will turn on for the PC's 10th birthday in 1991. When IBM unveiled the original PC, a major selling point was the fact that it was "personal". At last the frustrating hours of waiting for elf 4 1 time on a mainframe terminal were at an end for there, sitting proudly on your desk, was a gleaming monochrome PC with two floppy disc drives and a massive 256K of memory. It was computing heaven - freedom to do what you want, when you want and for as long as you like! Little more than a decade later, ' This 5.25-inch CD-ROM drive is made by Philips. A CD-ROM can typically store 660Mb of data or about 300,000 pages of text. 36 SILICON CHIP bigger the standalone PC is almost a thing of the past. The growing prominence of computer networks in the workplace is slowly taking the "personal" out of personal computing. The circle is complete once again everyone's data is gathered together on a hard disc rather than scattered over many different discs. But each user can still have information like call lists and other personal data stored on diskettes. With so much important information stored in one place, the importance of regular and reliable backups must not be underestimated. The skill of the person overseeing the network is also of considerable importance. So many users and so much information. In the standalone world, most users typically have a hard disc with around 20Mb of storage capacity. For the home or small business user, any thoughts of using a CD-ROM drive are laughable. When the CD-ROM is part of a network however, it starts to make much more sense. When you talk about optical storage technology, CD-ROM is the oldest. Generally it is used for publishing large amounts of information - such as dictionaries, encyclopaedias and databases - that don't require constant updating. Applications have progressed, however, from general reference material to more specialised data. Which is just as well since the major limitation of the CD-ROM is that it is a read only device. You can't update it or store new data on it. typically stores 1Gb (Gigabyte or 1000 megabytes) per side although Sony recently released a 30cm disc providing 6Gb of storage. The 35.5cm disc usually stores over 3Gb per side. Aside from the variations in disc formats, media types, recording techniques and rotation methods, WORM drives are usually made up of opaque recording material between two clear plastic plates. Philips' latest CD-ROM is the CM201. CD-ROM is a read-only device and is ideal for large databases that don't require constant updating. Philips and Sony have defined the standard for CD-ROM discs. This means all suppliers use the same protocols when creating their discs and all players can read the discs. The compact disc contains digitised data which can be audio, computer data or a combination of both. One CD-ROM can hold 660 to 680Mb of data - the equivalent of about 300,000 double-spaced pages of text. So much data on such a small device! Microsoft's Programmer's Library is delivered on CDROM and contains information on OS/2, MS DOS, Windows, networks and PC hardware. The disc has the MS-DOS encyclopaedia together with references to C, Macro Assembler, Basic, Pascal and Fortran, Peter Norton's Programmer's Guide to the IBM PC and PS/2, QuickC Programming, Advanced OS/2 Programming, volumes one to four of the Microsoft Systems Journal, 15Mb of sample code for use in your own programs and a whole lot more. CD-ROM drives will certainly become more appealing given the increasing size of operating systems and applications software. Computing requirements for realistic visual images on disc will pro- bably also increase demand for the discs. WORM drives To date though, the optical or WORM (Write Once Read Many) drive has provided the most practical answer to mass storage requirements. Access times for optical drives remain well behind those for the more familiar magnetic drives. WORM drives use lasers to record data at a very high density on a removable disc. Compared to CD-ROM, WORM drives are less prevalent. The drives themselves may be either standalone or organised in a kind of "juke-box" arrangement with a number of discs and an autochanger. Applications requiring permanent storage such as medical and taxation records, engineering drawings and plans, financial and insurance records, to name just a few, are the prime uses for WORM drives. WORM drives can use 13.3cm (5.25-inch), 25cm, 30cm and 35.5cm discs, while the CD-ROM has been more or less standardised to 120mm. Storage capacity on the 5.25-inch WORM varies from 300Mb to 600Mb per side. The 30cm disc A high powered laser is focused through the plastic plate to burn holes in one only of the WORM's recording material, to store the data bits. To access the other side of the disc, typically you need to remove the cartridge and turn it over, just like your trusty old record player. The data bits are read back when the laser focuses a lower power beam on the media. Usually, data written on one vendor's WORM drive is not readable on another, whereas CD-ROM has the advantage of being able to play any disc on any reader. Technologically, WORM is just behind the compact disc. Although you can write your own data to a WORM disc, you can't then change what is written. Laser video discs Laser video discs are ideal for storing large numbers of photographic images. Visitors to the IBM stand at Brisbane's Expo 88 would have seen the laser video disc in full flight. The archival value of the video disc system is considerable since alterations can be made onscreen to copies of the stored image. Images can be made clearer, reconstructed or changed without affecting the original photograph. A laser video disc can store in analog format a combination of stills and video images (up to 108,000 images on a 30cm disc). Laser video disc quality is considerably better than the conventional television image. Each disc is protected by an acrylic seal, like the compact disc. Thus, there is little likelihood of damage from mechanical wear and tear, like the magnetic medium, nor is there the possibility of magnetic interference. APRIL 1990 37 Designed by Philips, this cartridge-loading device protects the CD-ROM from direct handling. Also, because the data is sealed into the optical disc, it is less likely to be corrupted than other media during use. Erasable optical discs Erasable optical discs are the latest players on the mass storage scene. Rewritable magneto-optical (MO) disc drives use the 5.25-inch form and store up to 650Mb of data on optical media protected by a removable cartridge. The disc spins at around 3600rps, making it comparable to the traditional hard disc. However, access times tend to be somewhat slower. Magnetic hard discs still have a significant speed advantage and the $10,000 price tag for an erasable optical disc drive means they are not for the faint-hearted. The erasable optical disc, like the WORM disc, is made up of recording material between plastic discs. The discs work by magnetic orientation. At room temperature, recording material on a "blank" disc has a uniform magnetic orientation. However, when the temperature is raised significantly, you can alter the material magnetically. The Next Month in Silicon Chip The Mozzie QRP Transceiver This nifty little transceiver is an unconventional design. It is suitable for Morse and RTTY and puts out as much as 800 milliwatts at 3.5MHz from its internal battery pack. And it's nice and clean spuriae are less than -40dB. PLUS: Bonus 180-Page Dick Smith Catalog 38 SILICON CHIP drive head uses a laser to heat the target area and reverse the orientation. Once the material returns to room temperature, the reverse magnetic orientation remains. Thus, the varying magnetic orientations of the disc represent the data bits. Erasable optical discs are therefore ideal for backups since you can remove and re-use them. Erasing then rewriting the data requires one pass of the drive head to heat the target area and apply a uniform magnetic orientation. The second pass actually writes the new data. Data is read when the drive focuses a laser beam on the recording surface to determine the polarity of the surface, since reflected light changes according to the magnetic orientation of the disc. Again like the WORM drive, the erasable optical disc can only access one side of the disc at a time. It was not so long ago that 20Mb hard discs were "de rigeur" in the office environment. Even now, 20Mb to 40Mb is still adequate for most applications. Nor is hard development standing still. IBM has already demonstrated an experimental hard disc drive which stores a gigabit (one billion bits) of information on a single square inch of disc surface! Magnetic tape drives Throughout all this technological change, the magnetic tape drive is still the lowest-cost method of storing vast amounts of material. It is cheap to buy, high capacity, relatively easy to keep and catalog and simple to operate. The main disadvantage is the sequential nature of the tape. Waiting for a file right at the end of a large magnetic tape is not fun and certainly not recommended for the impatient. Tape backup systems, like backup to floppy disc, generally provide the facility to selectively backup and restore individual files, rather than the entire contents of a hard disc. The tape is usually housed in either a cassette or cartridge. However, it is subject to magnetic interference and is not everlasting. For long term record storage you really need a WORM or erasable optical drive. 1§:;l