Single Sided diskettes

[Marrr]

Once upon a time (or more precisely, almost 20 years ago), I set out to buy a box of diskettes for my Turbo XT. When I returned home, I realized I got wrong ones - Single Sided, and I hastily returned them. Years later I began to regret that, as I have never seen such diskettes since then, and they sure would be a nice addition to my collection...

But a miracle has happened, and I just got a bunch of 5.25" SSDD disks again. Well, I wasn't really surprised to see them practically identical to DSDD, they even format to 360 KB without any bad sectors, the only difference seems to be the sticker which reads "Single Sided...".

So, a question: was this a rule, or rather an exception? Were there 5.25" SSDD disks with magnetic media on one side only? Or with only one hole for the head?

Also, when were Single Sided drives dropped in PCs? I reckon first 5150s had SS, but later 5150s and XTs had DS, right?

 

[Fallo]

So, a question: was this a rule, or rather an exception? Were there 5.25" SSDD disks with magnetic media on one side only? Or with only one hole for the head?

Disks that weren't tested on both sides were labeled as SS. In most cases, there's no difference between them and DS disks.

Also, when were Single Sided drives dropped in PCs? I reckon first 5150s had SS, but later 5150s and XTs had DS, right?

The very first 5150s had only SS drives, but DS drives became available with the release of DOS 1.10 (May 1982). The SS drives were still offered until DOS 2.00 arrived (March 1983), and after that, only the DS drives were available.

 

[Chuck(G)]

Single-sided diskettes were usually double-sided diskettes where one side or the other failed to verify. The manufacturing machinery could flip the "cookie" so that the correct side always faced down. (Similar games were played with early DRAM--8K DRAMs could be gotten where only one half of a 16K DRAM was good--I've still got a few Intel ones in my hellbox. A suffix was applied to the part number to tell you which half to use).

When the 5150 came out, single-sided diskette drives were long out of fashion--IBM offered them because they were cheap. Most other vendors by 1982 offered DS drives as standard equipment.

 

[modem7]

More info for Marr:

The SS capacity used by DOS was 160KB (40 tracks of 8 sectors each 512B in size).
The DS capacity used by DOS was at first 320KB (2 sides of 40 tracks of 8 sectors each 512B in size).
DOS 2 upped the sector count to 9 resulting in a DS capacity of 360KB (2 sides of 40 tracks of 9 sectors each 512B in size).

 

[carlsson]

I also have a few single sided SKC floppies, formatted two sides on the Commodore 64 (thus a "flippy" with dual write protect notches). On some of those floppy disks the back side stopped to work after a couple of years and write cycles. I got the feeling the actual disk is thinner than most DS ones are, but perhaps I'm seeing things that don't exist or how to put it. Actually I have a whole box of NOS single sided SKC disks which I will try to use some day. I will then inspect them if they really look different than the usual double sided ones.