In the old days of digital video, if you weren't using an array of SCSI disks, you weren't doing digital video. It was common for digital video aficionados like me to spend $4000 for an 8 GB array, and I was astonished when it was able to achieve sustained throughput of 8 MB per second. That was 1994.

Now, eight years later, behold a landscape that I would not have recognized in the mid-nineties. With the advent of DV, suddenly those 8 megabytes per second are overkill. And, disk drives that can only offer 8 MB/sec sustained throughput are rare, indeed. In these days when even the lowliest computer is equipped with an ATA-100 drive that's easily capable of 20MB/sec sustained throughput, is SCSI necessary? By the way, notice I keep mentioning sustained throughput -- you may see the word "burst" when looking at disk specs, but keep in mind that this word means little for us DV jockeys. Video needs continuous, sustained throughput to keep from dropping frames.

Do the Math
Is it worth it to pay lots more money for a SCSI drive that may not offer you anything better than what you'd get with an EIDE drive connected via an ATA-100 or ATA-66 interface? In a word: No! If you're editing DV footage, even dual stream, SCSI is overkill. Now, don't mistake that statement to include uncompressed video editing. You'll need the big guns for that. But do the math: DV footage requires 3.6 MB per second throughput. Even the slowest disk on the market today can accomplish that. Now if you want to create real time dissolves and other effects, you'll need to double that number, but still we're only talking about 7.2 MB per second here. That's well within the performance capabilities of almost any modern disk drive you can buy today.

Tech Talk
That said, let's look at the technical aspects of this phenomenon. What is IDE? Compared to SCSI, it's a fairly new standard whose three-letter-acronym stands for Integrated Drive Electronics. Also known as ATA (AT stands for "Advanced Technology," referring to IBM's original design for personal computers, and the third letter A stands for Attachment), IDE originally could only handle disks smaller than 550 megabytes with throughput of only 2.5MB per second. So, a new standard was developed, called EIDE (for Enhanced Integrated Drive Electronics). It's blessed with more bandwidth, capable of 16.6 MB per second. Then, even more was needed, so Ultra IDE was created, sporting throughput of 33 MB per second. Subsequent iterations of the technology sped things up significantly, resulting in ATA-66 (66 MB per sec.) and ATA-100 (100 MB per sec.) and faster. Here's where the speed of the ATA disks met or surpassed SCSI. However, those throughput numbers are burst speeds, which don't mean much for digital video editors. In fact, very few drives can actually reach these quoted burst speeds, the rate at which one small piece of data can be transferred. More meaningful is the sustained throughput, needed when dealing with large contiguous files like DV footage.

One weakness of the IDE family comes into play if you want to use more than four disks in your computer. Unlike a SCSI controller, each IDE controller can accommodate only two IDE devices in a master/slave configuration. Motherboards can support two IDE controllers for a total of four drives. In this configuration, it's the master drive that manages the operations of both drives. The downside of this is that if the master drive fails, both drives are disabled.

SCSI
On the other hand, there's SCSI, which stands for Small Computer Systems Interface. It's a standard for connecting peripherals to your computer through a hardware interface. A great attribute of SCSI that used to be much more important than it is today is the fact that SCSI doesn't take any CPU resources, because its hardware contains a processor that does all the heavy lifting. The latest SCSI standard is Ultra320 which is theoretically capable of 320 megabytes per second.

The Bottom Line
Summing up, SCSI technology is surely a fine, fast and dependable way to get data to and from a disk, but the problem with all this wonderful hardware is that it's too expensive. For example, you can get a 72 gig SCSI disk for $780, while a 80 gig ATA-100 disk costs just $300. Since all this extra speed won't do you any good when you're working with DV, looks like that huge price difference is nothing short of totally compelling.

Charlie White has been writing about digital video editing since it was the laughingstock of the post-production industry. He's an Emmy award-winning producer and director for PBS, and Senior Producer at Digital Media Net. Reach him at cwhite@digitalmedianet.com