ABCs of CD-ROM

 

The term CD is no stranger to most of us and has been around for over a decade. Its technology was initially developed by a scientist and was later bought and owned by Philips. Thereafter, a long investigation by Philips and Sony had led to an agreement on the production standard which brought audio CD into the market for the first time. Soon it became an audio standard. Nowadays, audio CD has become a major source for music releases and has almost completely replaced LP. The same technology is used to produce CD-ROMs. In November 1984, Denon, Hitachi, and Philips demonstrated the prototype of CD-ROM drives and the products were delivered in the first quarter of 1985. In 1987 the High-Sierra and ISO formats were adopted. Since CD-ROM is a very good digital storage media, it quickly became a standard storage media in the computer industry. A general and technical comparison of CD-ROM and other storage media are summarized in the following tables :

Media	CD-ROM	Floppy	Tape DAT/V8	Harddisk
Durability	long lasting	volatile	medium	volatile
Transfer rate	slow	slow	fast	very fast
Price (media)	very low	low	medium	expensive
Price (drive)	low	very low	medium	expensive
Storage capacity	high	very low	very high	varies from high to very high
Random access	slow	slow	very slow	very fast
Cost effectiveness (cost/storage)	very high	low	very high	varies from low to very low
Compatibility	very high (ISO-9600)	high (DOS)	medium (tar format among UNIX)	low (incompatible even on same system)
Handiness	very handy	handly (depends on number of MB)	very handy	non-handy (both size and weight)

Media	CD-ROM	Floppy	Tape DAT/V8	Harddisk
Rotational speed (rpm - revolutions per min.)	200-500	360	-	3600
Storage capacity	650 MB	1.44 MB	5 GB/ 10 GB	? MB/ ? GB
Access time (average - max.)	300ms - > 1s	5.25in : 240 ms 3.5in. : 10 ms - 35 ms	1s - > 1 min.	10 ms - 50 ms
Data transfer rate (per second)	150KB (1x) 600KB (4x) 900KB (6x)	5.25in : 500KB 3.5in. : 0.5 MB	-	1 - 10 MB

* Please note that the data and figures given above may vary since the technology is changing so rapidly and that the specifications depend on the brand and model of the drives.

Factors to Consider When Buying a CD-ROM Drive

Although the price of a CD-ROM drive may be one of the most important factors in deciding which to purchase, there are other criteria to consider as well. Here is a list that will certainly help you to make your choice.

1. Manufacturer
   Different manufacturers may mean different reliability, different interface or different performance.
2. Internal/External/Both
   An external drive requires a separate power supply, an external connection cable, and comes with a casing. Hence, it needs more space than an internal drive. However, it is more cost effective because the same device can be shared among several computers. On the contrary, an internal drive does not require extra hardware therefore it is usually cheaper than the external ones. But before considering different types of drives, do bear in mind that not all of them have a choice of both internal and external models.
3. Caddies
   A Caddy is a case for the CD-ROM disc itself. Drives using caddies can be placed either vertically or horizontally while drives that do not require caddies must be placed horizontally. Caddies also serve the purpose of protecting the CD-ROM discs. Nevertheless, one disadvantage of using caddy drives is that when you lose your caddy, your CD-ROM drive becomes useless because you cannot place your CD-ROM disc directly into the drive.
4. Seek Time in milliseconds(ms)
   The shorter the seek time is, the better is the drive.
5. Transfer rate in Kilobytes(KB) per second
   The transfer rate is normally referred to as 61x, 2x and 4x; i.e. single speed, double speed and quadruple speed. And of course, drives with faster transfer rate are better, except that some software may claim that they can not work properly on drives that are too fast. Therefore fast speed drives with downgradable speed are the best. Now 6x drive is gradually emerging in the market.
6. SCSI , SCSI 2, non-SCSI
   Most CD-ROM drives have a 7SCSI interface, but SCSI drives require a separate SCSI controller if it is not already installed in the PC. A commonly used SCSI controller on PC is the Adaptec 154x. SCSI interface, a standard on most Macintosh and workstations. SCSI-2 drives have a higher transfer rate than ordinary SCSI drives. However, they need all the devices and the controller to be SCSI-2 standard in order to acquire the speed of SCSI-2 rate. Otherwise, all the devices will downgrade to SCSI performance only. Please note that non-SCSI drives, which may be 8IDE drives, do not require a SCSI controller.
7. PhotoCD compatible - (N=No, S=Single-Session, M=multi-session)
   Obviously drives that support 9multi-session are the best, single-session the second best and those that do not support 10PhotoCD are the worst.
8. CD-I and CD-Video
   Most newer drives support also 11CD-I and 12CD-Video. This feature refers to the ability to read and not the ability to play the CD-ROMs. CD-I and CD-Video require additional hardware or software to decode and play the data, for instance, 13MPEG decoder is required to play CD-Video.
9. Jukebox(Multi-disc)
   A multi-disc player, like the Pioneer one, may hold up to six discs and does not require frequent changing of disc and can permanently store commonly used discs.
10. Others
    Compatibility is one issue that you should not neglect. For example, you should check if your new drive can work properly with your existing hardware and software arrangements such as OS/2, Windows NT, Multi-media PC, Quicktime and so on.

Outlook

One single CD-ROM replaces over 250,000 sheets of A4 paper that would have piled up sky-high in your office and it is also equivalent to over 400 high-density floppy disks. Just imagine the old software installation method that requires you to insert and change floppies the whole time and you just sit there like a couch potato. With CD-ROM, software installation is much easier because now you simply answer a few questions at the very beginning and the computer would complete the rest for you; all you have to do is to prepare some tea or coffee and wait for it to finish.

Now CD-ROM holds not only text and numbers but also high resolution pictures, graphics, sound, video and multimedia - in fact any type of data that can be digitized. There is clearly a bright future for this advanced optical technology.

TERMINOLOGY
CD	Compact Disc
CD-DA	CD - Digital Audio
CD-I	CD - Interactive
CD-I Bridge	CD that is readable on both CD-I and CD-ROM/XA drives
CD-R	CD - Recordable (a type of WORM)
CD-ROM	Compact Disc - Read Only Memory
CD-ROM Mode 1	CD-ROM for computer data
CD-ROM Mode 2	CD-ROM for compressed audio data and video/picture data
CD-ROM/XA	CD - eXtended Architecture for computer data, compressed audio data and video/picture data
CD-Video	CD with VHS quality video compatible on multi-platform using MPEG compression
High-Sierra File System (HSFS)	This is normally referred to the same as ISO-9660 although there is actually a very minor difference
IDE	Integrated Drive Electronics
ISO-9660	A file system standard from International Standard Organisation used to store files and subdirectories used on CD-ROM
LP	Long Playing record
MPEG	Moving Pictures Experts Group
Multi-session	Written more than once
PhotoCD	CD storing digital pictures, format developed by Kodak
SCSI	Small Computer System Interface
WORM	Write Once, Read Many
1x,2x, and 4x	the times of transfer rate compared to standard CD-ROM 1x=150KB, 2x=300KB, 4x=600KB

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