10.3 Choosing a CD-ROM Drive
Ordinarily, you will purchase
a CD-ROM drive only when building a new system. CD-ROM drives
seldom fail, and replacing your current CD-ROM drive seldom makes
sense unless it is an elderly 1X or 2X unit. Even a 4X drive is
adequate for most purposes, including all but the most CD-intensive
games and multimedia applications, many of which are still optimized
for least-common-denominator 4X drives. Consider the following issues
when choosing a CD-ROM drive:
- Data transfer rate
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For most applications,
DTR is the most important performance
characteristic of a CD-ROM drive. DTR is most important if you use
the drive mainly for sequential data transfer, such as playing games
or loading software. Unless you have very special needs, any
name-brand $30 ATAPI 32X or 40X drive is more than sufficient for
anything you need to do. Purchase a more expensive drive only if you
play games directly from CD or use other applications that really
benefit from the higher DTR. Such applications are few and far
between.
- Average access time
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Average access time is important if you
use the drive mainly for random access, such as searching databases.
Although access time and DTR are not inextricably related—it is
possible to build a drive with a fast actuator and a slow motor or
vice versa—there is a fair degree of correlation. Typical
inexpensive ATAPI drives may provide true 100 to 200 ms average
access (although they are often marketed with inflated average access
performance numbers), while high-end drives, particularly SCSI
drives, may provide true 85 ms access. If you use databases heavily,
go with a high-end drive for its improved average access. Otherwise,
a typical ATAPI drive will do the job.
- Buffer size
-
Currently available drives have buffers ranging from 64 KB to 512 KB or
more. All other things being equal, the drive with the larger buffer
will provide higher performance. But all other things are seldom
equal, and a drive with a smaller buffer from one manufacturer may
outperform a drive from another manufacturer that has a larger buffer
and otherwise identical specifications. We recommend treating buffer
size as a minor issue when choosing a drive. If a drive is available
in two models differing only in buffer size, and the price difference
is minor, go with the larger buffer. Otherwise, ignore buffer size.
- Interface
-
CD-ROM drives are readily available in ATAPI/IDE, SCSI, USB, and
parallel interfaces.
The vast majority of CD-ROM drives installed in systems or sold
individually are ATAPI, which is inexpensive and adequate for nearly
any application. Make sure any ATAPI drive you buy supports DMA
(bus-mastering) transfer mode, which improves performance and greatly
reduces CPU utilization. SCSI drives typically cost $25 to $50 more
than equivalent ATAPI drives (in addition to the cost of the SCSI
host adapter, if your system is not already so equipped). Choose an
ATAPI drive unless the faster average access and higher sustained
throughput typical of SCSI drives is a factor (such as for high-speed
CD duplication) or unless the internal-only limitation of ATAPI is an
issue.
- Internal versus external
-
ATAPI drives are internal-only. Parallel and USB drives are
external-only. SCSI drives are available in either form. External
drives typically sell at a $50 premium over similar internal models.
Choose an internal drive unless you have a notebook, no externally
accessible drive bays available in your desktop system, or you need
to share the drive among multiple PCs.
- Mounting method
-
Nearly all modern CD-ROM drives use tray mounting. A few
drives still use caddy mounting, in which each CD is more or less
permanently inserted in a protective cartridge called a caddy. In
theory, tray mounting has two drawbacks: the tray mechanism is more
expensive and less reliable than the caddy mechanism, and the tray
mechanism does nothing to protect CDs from dust and physical damage.
In practice, caddies are expensive and more trouble than
they're worth. Some drives use a slot mounting
mechanism like that used by dash-mounted car CD players. This is in
theory the best compromise, but few such drives are available, and we
have had enough reports of problems with slot mounting mechanisms
that we recommend avoiding them. Unless you have compelling reasons
to do otherwise, choose a drive that uses tray mounting.
- Formats and disc types supported
-
Which formats a CD-ROM drive supported was a major issue back when
standards were still developing. Some drives, for example, did not
read Kodak PhotoCD discs. Most current drives support all formats and
disc types you are likely to need to read, with one exception: some
drives still cannot read discs written on CD-Rewritable (CD-RW)
media. Any drive you buy should support the following:
- Formats
-
CD-DA, CD-ROM Mode 1; CD-ROM XA Mode 2, Form 1 and Form 2;
Multisession (Photo-CD, CD-Extra, CD-RW, CD-R) Mode 1 and 2; CD UDF
(variable packets)
- Disc type
-
ISO 9660-HFS; Rockridge; CD-I Bridge (PhotoCD, Video CD); CD-I; CD-I
Ready, CD-Extra (CD-Plus); Enhanced CD; CD-R; CD-RW; CD+G; CD-Midi;
CD-Text
- Digital audio extraction (DAE)
-
If you will use the CD-ROM drive as a source drive for duplicating
audio CDs to a CD-RW drive, make sure the drive supports
digital audio extraction (DAE),
which is required to copy audio digitally. All current CD-RW drives
support DAE. Few CD-ROM drives shipped before mid-1998 fully support
DAE, although some models offer partial DAE support. A typical
DAE-capable ATAPI drive supports DAE at only a small fraction of its
rated speed. For example, our Toshiba XM-6402B 32X ATAPI CD-ROM drive
supports DAE at only about 6.8X (see Figure 10-1).
Many pre-1999 DAE-capable ATAPI 24X to 36X drives support DAE at only
1X or 2X. High-quality SCSI CD-ROM drives, such as the Plextor
models, support DAE at or near their rated read speeds. Attempting to
use DAE at a rate higher than the drive supports yields a
"Rice Krispies" dupe—full of
snaps, crackles, and pops (along with some hissing). If this occurs,
the only solution short of replacing the CD-ROM drive is to set your
CD-R drive to record at 2X or 1X.
In addition to DAE speed, the quality of DAE varies significantly
among drive types and models. In general, DVD-ROM drives provide
mediocre DAE quality. ATAPI CD-ROM drives vary, but most recent
name-brand models do a decent job of extracting audio. If you want
the absolute best available DAE quality, use a SCSI Plextor CD-ROM
drive.
- CD-ROM versus DVD-ROM
-
Although many CD-ROM drives are still sold, the widespread
availability of fast DVD-ROM drives at reasonable prices has greatly
shrunk the market for CD-ROM drives. Before you buy a CD-ROM drive,
consider buying a DVD-ROM drive instead. Modern DVD-ROM drives read
all standard CD formats, provide very high performance, and can (of
course) read DVD discs, something no CD-ROM drive can do. Although
there is still a place for high-end CD-ROM drives, primarily for
extracting digital audio and duplicating CDs, we think most people
who are considering an ATAPI CD-ROM drive would be better served by
spending $10 or $20 more for an equivalent DVD-ROM drive.
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Although they are less popular than they used to be,
CD changers are still available. These
drives allow you to insert from three to six individual CDs and
access them individually, often either by one shared drive letter or
by a separate drive letter for each CD. We have never had much luck
with these devices, although some people swear by them. They are less
popular than before because, with hard disk space at $4/GB,
it's faster, cheaper, and easier just to copy
multiple CDs to the hard drive.
We recommend avoiding CD changers
unless you need immediate access to multiple CDs that will not run
when copied to the hard drive. If you need access to only two or
three CDs, consider installing two or three ATAPI CD-ROM drives
rather than a changer. If you must have a changer, make very sure
that drivers are and will continue to be available for your operating
system.
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