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floppy disk question

O

Ozfer

Experienced Member
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Hey guys I just got a lot of new commodore stuff lately and since I now have commodore floppies, apple floppies, and PC floppies it is getting difficult to keep track of them all.

I have tried finding good reference information online that contains the standard sizes of floppy disks used in mainstream computers but it seems fairly rare to find this information and when I do it quite often conflicts with what I thought I knew. For example my new commodore 1541 disk drive states that it uses 5.25" SS/SD but I have never seen a SS/SD and don't know if they are referring to SS/DD? Plus when I looked up DS/DD drives I even found a site saying they were 720k but I have a brand new box of them sitting next to me that states 360k. Also would 5.25" hd drives be able to read all the previous types of disks(ss/sd, ss/dd ds/dd)? I am going to try to list the major type of floppy please help me fill in where my information is wrong or missing and hopefully this will be a useful reference.

SS = single sided, DS = double sided, SD = single density, DD = double density, HD = high density, QD= quad density, ED=Extended Density(quad density).

standard 3.5" DS/HD drives are compatible with DS/HD, DS/DD

8" storage
SS/SD 250k(ibm)
DS/SD 500K(ibm)
DS/DD 1.2M(ibm)

5.25"
SS/SD 90k?
SS/DD 160-180k(ibm)
DS/DD 360k(ibm)
DS/HD 1.2M(ibm)
SS/QD: ~360kB(DEC)
DS/QD: 720kB(ibm)

3.5"
DS/DD 720k(ibm) 800k(apple)
DS/HD 1.4M(ibm)
DS/ED 2.8M(ibm)
 
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5.25"
SS/SD was not used in IBM PCs much. Many PC controllers can't even do single density reads. But if you see a 5.25" system with less than 100kB capacity then it likely used SS/SD disks. IBM PC started with double density.
SS/DD: This was originally 160kB for IBM PC. Revisions to DOS increased that to 180kB. Apple and Commodore used the same disks with similar capacities which also changed depending on revision.
DS/DD: Yes, 360kB for IBM and several Apple and Commodore drives also used it. Probably the most frequently used 5.25" drive with different capacities depending on computer.
DS/HD: IBM 1.2MB
Now for an oddball you skipped, the so called quad density which fall between double density and high density. IBM did not sell quad density drives.
SS/QD: Frequently sold as 360kB so watch out for it. Don't make a mistake and buy one. More common on DEC systems.
DS/QD: 720kB when used by PC Compatibles.
Then there are the weird 5.25" drives which include Apple's Twiggy (1+ MB) and various DriveTec/Kodak drives which handled 3, 6 and 12 MB plus could read and write DS/DD disks. Both are rare but the chance of finding a system with one make looking at older computers more fun.
Edit: Unlikely to be found with IBM, Commodore, or Apple systems, but early drives were hard sectored. Disks for those are fairly obvious by having an extra ring of holes. Some other disks will be flippies; single sided but with a second index hole so the disk could be flipped over and written on the unused side. This can be confusing.

3.5" The 2.8MB drive was marketed as ED. There was also very early on single sided 3.5" drives (400kB on Mac; 360kB for systems following an MS-DOS style format like MSX or Atari ST).

Sony had an even earlier single sided 3.5" drive with different rotation rates and lower capacity. Something to watch for because some were manufactured before the automatic shutter was developed.

Now there are more than 500 known formats for drives especially if you look at all the small CP/M vendors. Some, especially tricky capacity maximizing formats used in backup software, require very exact matches to the system that created the format to have any chance of reading it.
 
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On IBM 160K and 180K are both Single Sided/Double Density 48TPI (40 track). The difference is the way DOS 1.x and 2.x formatted them. DOS 1.x used 8 sectors per track and DOS 2.x used 9 sectors per track.

IBM PCs never officially used Single Density disks, although some controllers support that internally.

A SS/SD 5.25" 48TPI disk would hold ~90K depending on how it is formatted.

A DS/DD 5.25" disk can be used as SS/SD, SS/DD, or DS/SD. You just don't make use of all of the space.

Most DS/DD 5.25" are rated for 48TPI (40 tracks), but it is technically possible to format them to 720K using a 96TPI (80 track) drive such as a High Dencity 1.2mb drive in low-density mode. 96 TPI double/low density disks are sometimes referred to as "Quad Density".

The exact amount of usable disk space on a disk can vary depending on how the system lays things out on the disks. So it can be confusing, especially when dealing with multiple platforms.
 
Are we talking about media types or formats for them?

If we're talking media, then there are definite differences in 8" that mostly have to do with the placement of the index holes. The medium ("cookie") is the same.

In 5.25", there are differences in high-density versus low-density media--the "cookie" in the high-density version has a different coating formulation (higher coercivity) than the low-density one.

In 3.5", there are differences in the cookie formulations (2D, HD, and ED), indicated by the placement of the "media type" hole. Manufacturers sometime label these by "raw capacity" as 1MB 2MB and 4MB media.

In addition, there are also hard-sectored 8" and 5.25" media--with the exception of some 8-sector Memorex 960 8" media, all 8" hard sectored disks are punched for 32 sectors plus index. The picture for 5.25" hard-sector floppies is a little more diverse, with 10- and 16-sector punchings most common.

Note: I'm not including "sui generis" media, such as Imation Superdisks or Drivetec 5.25" media, nor Amlyn 5.25"....

As for what and how the basic formatting patterns and modulation method being used, that's a different question entirely. Mostly, labeling for things such as QD versus DD versus SD is irrelevant. For example, I have a stack of 5.25" disks right by my computer that are labeled "1S 4D"--they're basically "360K" floppies.
 
Thanks for the help guys your answers have been very informative. I kinda wanted to know about the types and formats for the common floppies to get a better understanding of what is compatible with different computers I come across.

So would DS/DD 5.25" disk work as single sided in a commodore 1541 disk drive or do I need to find SS/SD 90k disks and if so does anyone know how I could use both sides? Also since it seems that it sometimes even varies by the individual specific type of floppy drive and brand of media especially when you use 8" disks they may only be readable with the machine that created them? I have very little experience with 8" floppies since I have never owned any or had a computer that could use them.
 
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DS/DD disks will work fine with a 1541. That at least I do know. No disk has problems if you ignore one side. Most disks labeled as single sided were actually capable of double sided use; some single sided disks have flaws on the unused side but manufacturing improvements soon got rid of the problem. Single density and double density use the same disk; how the controller worked was what changed.

Please note on the label or disk sleeve as to which machine created the disk and if it is single sided or a flippy disk. It will reduce the chances of inserting the disk in the wrong system and not seeing the content. When owning many visually identical disks for very different systems, labeling is the only way to keep things straight.

I will let Chuck(G) respond to the query about 8" drive types. I think I know this but I am having trouble writing something clear.
 
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Again, the fact that you've got a 5.25" floppy that's marked DSDD doesn't mean that any machine can read it-or even image it. A floppy drive is, by and large, a very dumb device. You could probably take a track off an old Beatles album and feed it into the write input of the floppy drive and get something recognizable out. And schemes for getting things onto floppies are about as diverse as anything can be.

As regards 8" drives, the same picture obtains. Say, for example, you've got an S100 system that reads and writes soft-sectored double-density media. Does that mean that you can read Intel MDS 8" double-density mdedia? Nope--the MDS uses an encoding technique called MMFM (or M2FM), where the S100 system probably uses MFM. How about reading a double-density 8" floppy from a DEC RX02? Nope--the DEC uses FM sector headers with modified MFM data fields.

But 8" media does have a physical convention for single- and double-sided and hard-sectored floppies--in addition to the encoding method used.
 
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