|The stupid question is the question not asked|
It was due mostly to SATA not (as far as I'm aware) being fully hot-swappable (at least, not on BSD). Or, looking at things another way, it was due to the BIOS on another computer I was working on not being able to properly handle the SATA hard drive and the ATAPI CD drive at the same time.
See, we had this new computer, on which we wanted to install a certain OS distribution (a fairly special-purpose one, which happened to be based on (a rather old version of) slackware), but its BIOS had only two options for how to handle SATA: either it could be set up in "legacy" mode, in which case the SATA drive actually masked the IDE channel (and any drives on it) entirely, or else it could be set up in "native" mode, in which case the BIOS did not see the SATA hard drive at all. (A fully installed and booted OS with the proper driver could perhaps work around things and use the SATA drive in this mode, but the OS booted from the installation CD was not able to do that.)
So I brought both the hard drive and the CD to my FreeBSD workstation, which I turned off, plugged in the SATA drive there, booted back up, created a small partition on the SATA drive, copied over the data from the CD to there, then shut back down, took the SATA drive back out, restarted my FreeBSD workstation so it could resume its normal duties, took the new SATA drive back to the new system, and proceded with the installation. I had to make some modifications to the installation script to get it to use the hard drive partition in lieu of a CD drive, but it did work.
Actually, I had to do this twice, because for some reason the first time I did't quite get all of the package files from the CD copied onto the SATA drive, and did not become aware of this fact until later when I was partway through the install process.
So my FreeBSD workstation had downtime *twice*, due to a flaw in the BIOS of another computer. Why on earth the BIOS makers decided not to allow the SATA drive to be treated as an _additional_ IDE channel is entirely beyond me.
We're working on a six-year set of freely redistributable Vacation Bible School materials.