The Osborne 1 was a luggable computer that contained a pair of 5.25-inch floppy drives. According to https://en.wikipedia.org/wiki/Osborne_1

Adam Osborne decided to use single-sided disk drives out of concern about double-sided drives suffering head damage from rough handling.

Is there a nonobvious reason why single-sided drives should be less vulnerable to this? Did other portable computers make the same design decision?

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    The technology was quite new at the moment. He might have been overly cautious due to lack of usage data. Commented Dec 27, 2019 at 13:18

1 Answer 1


In a double-sided drive, there are two heads which are necessarily closely spaced, facing both sides of the thin magnetic-coated disc once it is inserted. The concern would have been that the heads could collide with each other if the drive was jarred.

However, the drive designs I'm familiar with have a mechanism to hold the heads and drive spindle away from the disc until the drive door is closed (or, for the 3" and 3.5" stiffies, until the hard casing is detected in the inserted position). This is to permit the disc to be inserted by an untrained user without damaging the disc, but it would also hold the heads apart from each other so that they could not collide.

If the drive were jarred with a disc inserted, the heads would collide with the disc surface - but that's also true of a single-sided drive. I think floppy discs are a bit more tolerant of that than hard drives, mainly due to the lower speeds involved.

In practice, double-sided drives became common and did not have a reputation for fragility. I have had several laptops (and even an 8088-based Amstrad luggable) with 3.5" double-sided drives, some of which had decidedly rough handling over the years but gave no trouble.

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    The problem with double sided drives are that when the heads collides with the surface, they also collides withe each others through the thin surface. This is what makes the damage. Floppies where disposable, and cheaper than one or two read/write heads (+someone changing them). In a single side drive the head would only crash into the soft floppy.
    – UncleBod
    Commented Dec 26, 2019 at 10:19
  • @UncleBod There needs to be some part on the opposite side to the head to give correct contact between floppy and head. I don't think you get reliable operation if there is just air on the other side. Commented Dec 26, 2019 at 11:03
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    The difference between single sided drives and double sided ones, where head collisions are concerned, is the double sided drives have the potential for the heads to collide with one another, pinching the disk surface between them. Single sided drives typically have a pad on the non-active side, supported against the disk surface with a spring of some sort. In the extreme, there really isn't a hard head collision case with single sided drives. In my experience, there were no meaningful handling impact differences. (I was rough on drives)
    – Spud
    Commented Dec 26, 2019 at 17:11
  • @Spud: Would there have been any difficulty constructing a drive so that each head would be placed to the left side of the access slot, viewed from its side, so that the heads weren't actually directly opposite?
    – supercat
    Commented Dec 26, 2019 at 19:37
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    I think floppy discs are a bit more tolerant of that than hard drives, mainly due to the lower speeds involved. Floppy discs are designed around heads touching the platter, similar to how magnetic tape rubs across the heads in a player/recorder/drive. Hard drives are designed around them floating above the platter on a cushion of air.
    – ssokolow
    Commented Dec 30, 2019 at 11:06

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