Not that I think it's going to happen, but observing how slow areal density increases have become in recent times (1TB disks debuted back in 2011 and are still not far behind the state-of-the-art), it would be fun.
For the uninitiated: The first form factor for PC HDDs — and floppy drives — was known as 5.25″ full height, although none of the dimensions were really 5.25″: Width was 5.75″ (146mm), height was 3.25″ (82.6mm), and depth was 8″ (203.2mm) — talk about HUGE. The disk diameter in those drives was usually 130mm (5.12″). Then a version with half the height was made — and remains in use for optical drives (although with the depth reduced on newer models). Early 3.5″ HDDs were the same height as those, but they were soon to be 1″ (25.4mm) high (referred to as low-profile, or sometimes as “third height” even though it's a bit less than that), like the 3.5″ FDD (although the half-height form remained in use for high-capacity enterprise drives up to 2001 — the last of which was Seagate's Barracuda 180); width is 4″ (101.6mm) and depth 5.75″. Disk size is 95mm on drives up to 7200RPM; faster-spinning drives used smaller media to reduce seek time and power consumption. Some drives are even thinner, of course with only 1 disk inside (or 2 in Seagate's Decathlon/Medalist SL family of the mid-90s).Let's go with 8 disks. (Ancient enterprise drives had up to 12 but that was with much lower areal density, so they could make them thinner.) Some basic calculations suggest that:
- At 7200RPM, the drive would overheat unless actively cooled.
- At 5400RPM, the drive would get noticeably warm, but not too hot (unless installed in a fanless plastic enclosure).
- At 4200RPM, it could be considered a “green” drive.
- 3600RPM should be a piece of cake (by the standards of HDD engineering, anyway).
The main engineering problem would presumably be with the spindle bearings, as the added mass would put more stress on them (especially under shock conditions). (The aforementioned Barracuda 180 was only rated for 150G @ 2ms non-operational shock. Granted that was with ball bearings, and fluid-dynamic bearings are tougher — but even they have their limits.) The drive would also take quite a while to spin up (unless you raised the spin-up current to something ridiculous).
But probably the main reason why such a drive wouldn't be viable, is simply because half-height drives physically won't fit most systems. An array of five 8-disk drives may be a tad more reliable overall than one of eight 5-disk drives — or may not be. At least in the past, the difference in reliability between drives of the same series with different head counts would pale into insignificance compared to the differences between series, and the influences of how the drives are treated. (Granted, drives with fewer disks will draw less power and therefore run cooler, all else being equal. But that's an
indirect effect, and you can compensate with more — or larger, or faster — fannage.)
So I don't think the "retro" appeal of such a drive would be enough to sell it.
