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are stamped
by the vendor, and once stamped, they cannot be erased and filled with new data. To read a
CD, you need a CD-ROM player. All CD-ROMs conform to a standard size and format, so you
can load any type of CD-ROM into any CD-ROM player. In addition, CD-ROM players are
capable of playing audio CDs, which share the same technology. CD-ROMs are particularly
well-suited to information that requires large storage capacity. This includes color large
software applications, graphics, sound, and especially video.
Also called a CD-ROM drive, a device that can read information from a CD-ROM. CD-ROM
players can be either internal, in which case they fit in a bay, or external, in which
case they generally connect to the computer's SCSI interface or parallel port. Parallel
CD-ROM players are easier to install, but they have several disadvantages: They're
somewhat more expensive than internal players, they use up the parallel port which means
that you can't use that port for another device such as a printer, and the parallel port
itself may not be fast enough to handle all the data pouring through it. There are a
number of features that distinguish CD-ROM players, the most important of which is
probably their speed. CD-ROM players are generally classified as single-speed or some
multiple of single-speed. For example, a 4X player access data at four times the speed of
a single-speed player (also see Understanding CD Burner Speeds in the Did You Know . . . ?
section of Webopedia). Within these groups, however, there is some variation. Also, you
need to be aware of whether the CD-ROM uses the CLV or CAV technology. The reported speeds
of players that use CAV are generally not accurate because they refer only to the access
speed for outer tracks. Inner tracks are accessed more slowly. Two more precise
measurements are the drive's access time and data transfer rate. The access time measures
how long, on average, it takes the drive to access a particular piece of information. The
data transfer rate measures how much data can be read and sent to the computer in a
second. Finally, you should consider how the player connects to your computer. Many
CD-ROMs connect via a SCSI bus. If your computer doesn't already contain such an
interface, you will need to install one. Other CD-ROMs connect to an IDE or Enhanced IDE
interface, which is the one used by the hard disk drive; still others use a proprietary
interface. Acronym for small computer system interface. Pronounced
"scuzzy," SCSI is a parallel interface standard used by Apple Macintosh
computers, PCs, and many UNIX systems for attaching peripheral devices to computers.
Nearly all Apple Macintosh computers, excluding only the earliest Macs and the recent
iMac, come with a SCSI port for attaching devices such as disk drives and printers. SCSI
interfaces provide for faster data transmission rates (up to 80 megabytes per second) than
standard serial and parallel ports. In addition, you can attach many devices to a single
SCSI port, so that SCSI is really an I/O bus rather than simply an interface. Although
SCSI is an ANSI standard, there are many variations of it, so two SCSI interfaces may be
incompatible. For example, SCSI supports several types of connectors. While SCSI has been
the standard interface for Macintoshes, the iMac comes with IDE, a less expensive
interface, in which the controller is integrated into the disk or CD-ROM drive. Other
interfaces supported by PCs include enhanced IDE and ESDI for mass storage devices, and
Centronics for printers. You can, however, attach SCSI devices to a PC by inserting a SCSI
board in one of the expansion slots. Many high-end new PCs come with SCSI built in. Note,
however, that the lack of a single SCSI standard means that some devices may not work with
some SCSI boards. The following varieties of SCSI are currently implemented: SCSI-1: Uses
an 8-bit bus, and supports data rates of 4 MBps SCSI-2: Same as SCSI-1, but uses a 50-pin
connector instead of a 25-pin connector, and supports multiple devices. This is what most
people mean when they refer to plain SCSI. Wide SCSI: Uses a wider cable (168 cable lines
to 68 pins) to support 16-bit transfers. Fast SCSI: Uses an 8-bit bus, but doubles the
clock rate to support data rates of 10 MBps. Fast Wide SCSI: Uses a 16-bit bus and
supports data rates of 20 MBps. Ultra SCSI: Uses an 8-bit bus, and supports data rates of
20 MBps. SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra
Wide SCSI. Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps. Wide Ultra2
SCSI: Uses a 16-bit bus and supports data rates of 80 MBps. |
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