Compatibility Issues

With all the different types of SCSI hardware being manufactured, compatibility problems are bound to come up one way or another. Fortunately, all SCSI standards are designed to be backwards compatible. At least, that's what the designers intended. The reality is that you are never guaranteed to have any two different SCSI devices work reliably. It's best to make sure you have the same type of hardware (ie. all Ultra160 devices, etc). Mixing different types might not always work, and you'll pretty much be running at the slowest device's speed anyway. Is your old host adapter going to be compatible with that new Ultra320 hard drive you just bought? Do you have to buy a new one? Most of the modern SCSI standards are compatible with each other. The only real issue is mixing different bus widths and signaling methods. Planning is definitely a good thing when you want to build a SCSI system. You don't want to be stuck with devices that don't work with each other, especially expensive ones.

SCSI Vs. IDE/ATA

Now that you know what SCSI is and the many different standards involved in the spec, you can see that it is more than just an interface. IDE/ATA is cheap and easy to implement, but it isn't as feature packed as SCSI. Which one is better? Well, in terms of all out features and performance, SCSI definitely wins out. The transfer speed of SCSI is reaching 320 MB/s already, while IDE devices are still in the sub 100 MB/s stage. Even with ATA/100 100 MB/s is rarely seen. SCSI is also very good when it comes to multiprocessing. Operating systems that take advantage of this will see higher performance from SCSI. Also, SCSI hard drives are faster than IDE drives. I mean 10,000 rpm SCSI drives have been out for some time now. Only recently have IDE drives even come close to that speed. So if SCSI is so great, why isn't everyone using it? Well, the cost is usually what deters most people. Integrated SCSI host adapters are more expensive to implement than IDE controllers. The SCSI devices are also more expensive than their IDE counterparts. You definitely pay a premium if you want to use SCSI. If you're only have simple applications, SCSI isn't going to be that much faster than IDE/ATA. It's the more complex applications that SCSI wins out.

Also for the average individual, all the different SCSI types and configurations can be very confusing. Compatibility is also another issue. Is the host adapter you bought going to work in your system, or is that new 10,000 rpm drive going to work with your old host adapter? An IDE/ATA system is much easier to setup and put together compared to a SCSI system. You don't have to worry about termination, bus width, signaling methods, and addressing. However, SCSI can support up to 16 devices on a given chain, compared to only 2 for IDE/ATA. You have a lot more flexibility when it comes to physical installation since SCSI cables can be quite long. It's clear that SCSI is for the more performance hungry individual where money is really not an issue. Server systems that need the performance often use SCSI in conjunction with RAID. For the average user I'd recommend just sticking with IDE/ATA, and save yourself some cash. Unless of course you have more money than you know what to do with, then there's no contest.