Section 10.3. Choosing a CD-ROM Drive

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

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

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.

Figure 10-1. Using Adaptec Easy CD Creator to test a 32X Toshiba CD-ROM drive shows that it supports DAE at 1017 KB/s (~6.8X), high performance for an ATAPI drive

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.

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.