Although drive specifications are of the utmost importance, you should also consider other factors and features when evaluating CD-ROM drives. Besides quality of construction, the following criteria bear scrutiny when making a purchasing decision:

• Drive sealing

• Self-cleaning lenses

• Internal versus external drive

Drive Sealing

Dirt is your CD/DVD drive's biggest enemy. Dust or dirt, when it collects on the lens portion of the mechanism, can cause read errors or severe performance loss. Many manufacturers seal off the lens and internal components from the drive bay in airtight enclosures. Other drives, although not sealed, have double dust doors—one external and one internal—to keep dust from the inside of the drive.

All these features help prolong the life of your drive. Some drives are sealed, which means no air flows through the chamber in which the laser and lens reside. Always look for sealed drives in harsh industrial or commercial environments. In a standard office or home environment, it is probably not worth the extra expense.

Self-Cleaning Lenses

If the laser lens gets dirty, so does your data. The drive will spend a great deal of time seeking and reseeking or will finally give up. Lens-cleaning discs are available, but built-in cleaning mechanisms are now included on virtually all good-quality drives.

This might be a feature you'll want to consider, particularly if you work in a less-than-pristine work environment or have trouble keeping your desk clean, let alone your drive laser lens. You can clean the lens manually, but it is generally a delicate operation requiring that you partially disassemble the drive.

Also, damaging the lens mechanism by using too much force is pretty easy to do. Because of the risks involved, in most cases I do not recommend the average person disassemble and try to manually clean the laser lens.

Internal Versus External Drives

When deciding whether you want an internal or external drive, think about where and how you're going to use your drive. What about the future expansion of your system? Both types of drives have advantages and disadvantages, such as the following:

• External enclosure. These tend to be rugged, portable, and large—in comparison to their internal versions. External drives are ideal for sharing a drive with multiple systems or especially with laptops or notebook portable systems.

  Parallel port drives are very portable and supported on a broad range of machines, but USB drives are a better choice for Windows 98 or later systems that have USB ports. Connect recent drives to the faster USB 2.0 port for best performance. SCSI drives are also ideal for external configurations because performance is even better than with internal ATA drives.

  If each PC has its own SCSI adapter with an external connection, all you need to do is unplug the drive from one adapter and plug it in to the other. I use SCSI drives extensively, and with SCSI I can get the same level of performance when the drive is connected to my laptop as when it is connected to a desktop system.

  If you have an IEEE-1394 (FireWire, i.Link) port and don't have a USB 2.0 port, this port type provides speed comparable to SCSI and USB 2.0 and the hot-swappability of USB. Some optical drives are now equipped with both USB 2.0 and IEEE-1394 ports.

• Internal enclosure. Internal drives won't take up any space on your desk. Buy an internal drive if you have a free drive bay and a sufficient power supply and you plan to keep the drive exclusively on one machine. The internal drives are also nice because you can connect the audio connector to your sound card and leave the external audio connectors free for other inputs. Internal drives can be ATA or SCSI.