There are two major interfaces used to connect disk drives of various types in computers nowadays (there used to be more, but schemes like MFM, RLL, and ESDI are obsolete at this point). IDE (or its improved version EIDE) is the most common; most modern motherboards include an IDE connector or two, commonly used to connect hard drives and CD-ROM drives. You can have two drives per cable, so the two connectors provided on your average system lets you connect four drives. IDE drives are cheap, ubiquitous, and their performance is acceptable for most purposes. At the upper end of the market, SCSI drives are all you'll find. SCSI supports a variety of peripherals, everything from hard drives to scanners. A properly configured SCSI system supports at least 6 devices, which can be either internal or external to the computer, and can easily outrun any IDE configuration. The downside is that in most cases you'll need a SCSI controller card to connect everything with, and the devices themselves usually have a price premium associated with them (a typical SCSI drive costs at least $50 more than its IDE brethren, although that gap has been getting narrower recently). Creating a CD-R is definitely the sort of intensive task that SCSI performs better at then IDE; accordingly, all the CD-R drives out there use a SCSI interface. I'll mention IDE drives occasionally, but understand that you're going to have to come to grips with at least some SCSI details in order to get a CD-R going. I never use IDE drives for the systems I personally use, as I find them to cause more problems than the cost savings is worth, even if the SCSI configuration gets to be ugly sometimes. Understand, though, that SCSI is usually pretty easy to deal with if you've only got a small number of devices to attach; it's only because you can hook up a big stack of devices that it can become a pain.
This doesn't necessarily mean you need to abandon your existing hard drive if it's an IDE model, and it also doesn't mean that just because you've got a SCSI drive that it will be good enough. First off, your drive needs to have sufficient capacity. CD data can take up to 650MB; add in the size of temporary files need to actually burn that data, the OS, and other such overhead, and you really need at least 1GB dedicated to CD-R use. That over 1GB drive needs to have a particular set of performance characteristics as well. Foremost, it must be capable of keeping up with the sustained transfer rate involved. The unforgiving, constant nature of CD-R writing means that you drive needs to outrun that CD laser by a good margin. Unless your drive is old, this shouldn't be a problem; any good 1GB drive I know of made in the last few years should be fast enough to keep up, at least for single speed writing. The other major factor is how fast your drive can find things on the disc. If you're writing a series of files contained on a drive, the drive needs to move its heads to the area each file's data is stored at in order to transfer that data. The usual measure of how fast your drive can do that is the seek time; Incat's manual says that any drive with a seek time over 19ms has no hope of keeping up with a CD-R.
The final piece of ugliness to consider is something called thermal recalibration. Like any other metal, the pieces involved in a drive expand and contract as the drive heats and cools. To keep the drive aligned properly, most hard drives occasionally stop for a small period of time to recalibrate themselves. If your drive does this too frequently, or takes too long, your CD-R can crap out while it's waiting for the drive to stop fiddling with itself, and you're left with another CD-coasteR. There are a variety of drives now on the market that either delay their calibration when drive activity is occurring (most modern Micropolis drives are supposed to do this) or use a different sort of scheme altogether (some of Quantum's drives use a continuous calibration technique that avoids this issue altogether). Those are just samples; many manufacturers offer drives have the designation that they are A/V rated, which usually just means a more intelligent calibration scheme is used. In some cases, a minimum sustained transfer rate is guaranteed as well.
How much you need to worry about drive recalibration or transfer rate is determined by the buffer size on the drive you get and how fast you plan on writing CDs. Check the math first. If you had a forgiving CD-R drive, like the popular HP 4020I with its 1MB buffer, at the single speed rate for audio of 172KB/s, you've got over 4 seconds worth of time to waste with calibration before you're got a problem (not over 5 like you'd think at first, since you need time to fill the buffer back up when it's near empty). Now, my Yamaha drive can write at 4X speed, which is 688KB/s on audio tracks. Since the buffer on the drive is 512KB, that means that a one second hiccup with that configuration would kill the CD-R. Not a lot of room for error there, and these simple figures don't include the overhead involved in all these processes; if you run the numbers and your drive seems like it could just keep up, it probably won't. The moral is that if you don't need high speed writing, you can always run your CD-R at a slower speed than the maximum available one and possibly get away with a hard drive that it sluggish or has a long recalibration time. But if you want to write things at high speed, you're going to make sure you've got some serious drive hardware. My system worked fine doing some tasks even at quad speed with a Micropolis 4221W, which is a 2GB Wide SCSI drive. Since I've found that 2GB gets eaten almost immediately when you start doing serious work with CD- R, I've since added a 4GB Micropolis 3243WAV, a 4GB Wide SCSI drive that is A/V certified. This is an excellent drive, and I highly recommend it; not even the slightest hint of a problem writing, even at 4X speed. One thing to watch out for, you do need to be very careful to keep it cool; I've got 3 fans in my big tower case to keep the two drives from running too hot and that's just sufficient. Heat build-up problems are getting to be the norm with every multi-GB high-speed drive nowadays, so I wouldn't recommend just dropping one of them in any old case without checking the heat inside first; the running drive should be warm to the touch, but if it's getting hot enough that you want to pull your hand away, you're in the danger zone and the expected lifespan is greatly reduced. Try and space any hard drives as far away from each other as possible in the case as well.
Maybe you don't need 6GB of storage like I do, but it really is worth the trouble to get a good hard drive regardless; CD-R just makes it more compelling. Grabbing a random computer magazine, every drive manufacturer makes IDE drives currently that hold 2GB, have an access time below 12ms, and whirl at least at 4500rpm, all for less then $300. Any of these should be fine for beginning CD-R work, but may cause some problems as you gear up to higher recording speeds; that's when you need to be using some of the top performing SCSI drive (the Micropolis drives I own have access times less then 9 ms and spin at 7200 rpm). Drives capacities over 512MB have their own set of problems involving partitioning, DOS compatibility, and tons of other things; drives over 2GB are even worse. This is not the place for discussing all of those problems, but be warned that getting your computer and operating system to recognize all the drive you bought may end up being its own unpleasant exercise. I had to repartition my system well over a dozen times (trying a couple of different head/sector/cylinder translation modes) before I found something that worked with every operating system I wanted to run (DOS, Win 95, Win NT, and a couple of UNIX variants). I highly recommend PowerQuest's Partition Magic for dealing with the partitioning chore (simply being able to format a FAT partition in a second instead of waiting for the DOS format to scan everything is worth the price of admission when you get into multi-GB land), and V- Communication's System Commander is great for dealing with multiple OSes, especially if one of them is Win 95.
Along with the general problems high capacity drives cause with DOS, there’s also the issue of cluster size. DOS organizes your hard drive into clusters, which consists of a number of sectors on the drive. How many depends on how large the formatted capacity of your drive is. Larger partitions use larger clusters. This impacts you in two ways. First, more space is wasted if your partition size is larger and you have many small files. Second, the overall access speed to small files becomes greater as the cluster size increases. Large cluster sizes can cause systems with marginal performance to have more problems keeping up with the speed of CD-R writing. If you are having performance problems, and your cluster size is large (typically, greater than 16KB), you should consider using small drive partitions to improve things.