hard drive history

Photo: Red Hill.

The Bigfoot principle

The Bigfoot family of drives was intended to provide reasonably fast, reliable storage at the lowest possible cost per megabyte. Quantum achieved this by using a 5.25 inch form factor — the same size as a CD-ROM drive or old-style floppy. But don't get the idea these mid-1990s drives were low-tech. The larger 5.25 inch platters allowed more data to be stored than was possible on a standard 3.5 inch disc, and despite the slow 3600 or 4000 RPM spin rate, the actual speed at which data passed under the read head was very good — again, because of the increased circumference. The result is that Bigfoot drives used to have excellent data transfer rates, faster than most 4500 RPM 3.5 inch drives, and they cost less to make.

There were, however, some significant performance penalties from the large form factor. Average seek time for a typical Bigfooot was only fair at between 12 and 14 milliseconds. (An excellent achievement for such a big drive nevertheless.) More importantly, the latency was very high. Latency is the time (on average) that a drive spends waiting for the required data to pass under the read head once the head has been positioned over the correct track. If you think about it, it is obvious that latency is directly related to drive RPM. A drive's actual access time is composed of three things: a small amount of command overhead ("thinking time"), the seek time (as the head moves to the correct track), and the latency (as the head waits for the correct sector to rotate under it). We don't usually quote latency figures as they are directly related to spin rate and don't vary for any given RPM. (The faster the spin rate, the lower the latency.)

Consider the performance figures for some representative 4GB drives. Notice how poorly the Bigfoot compares:

Looking at the right-most column in the table, notice how much difference there is in the overall access times. The two SCSI drives (the WD and the Cheetah) had double the performance, but cost almost $1000 more than an IDE unit. However, the 3.5 inch Medalist was only about $30 more than a Bigfoot, and noticeably faster, while another $30 got you a much faster 5400 RPM IDE like the Deskstar 4 (or Quantum's own Fireball ST for that matter).

The Bigfoot theory was certainly interesting, and Quantum did a great job developing these drives as far as they did, but they really only made sense where cost was much more important than speed. If you were spending two or three thousand dollars on a new computer system — which was normal in those days — you were wise to do yourself a favour and specify a 5400 RPM 3.5 inch drive.

We never sold them new but we used to see Bigfoot drives in the workshop from time to time, and they were always quite noticeably slower than 3.5 inch drives, even slow ones. Incredibly, we once saw a Bigfoot factory fitted to a top of the range Pentium Pro system. This was the moral equivalent of putting four-inch budget tyres on a V8. (It ran more like a Pentium-90 than a Pro, and Hewlett-Packard should have been ashamed of themselves.)

Quantum used to have an easy to read and very interesting white paper on 5.25 inch drive performance, which is doubtless gone by now. It was interesting in two ways. Firstly it pointed out a non-obvious advantage to the larger form: although it has higher latency and slower seek, with more data per track the 5.25 inch drive has to switch heads and seek less often. Secondly, Quantum applied this with a transparently self-serving example, comparing a 2.5GB Bigfoot with a long-obsolete 4500 RPM 850MB 3.5 inch Trailblazer. For a fair comparison, they should have used a (then current) Fireball ST or TM — even the budget model 4500 RPM Fireball TM was easily faster. So read with care!

Here at Red Hill, we always used 3.5 inch drives for everything, even the entry level. The few dollars we could have saved by using Bigfoot drives for our lowest-priced systems simply didn't justify the performance hit.