Formatted diskettes

[bluejay]

I have a couple IBM Formatted 1.44mb diskettes. Does this mean the disk is hard sectored and cannot be used on a Macintosh, or does this mean that it is simply formatted from the factory, and can be re-formatted for use on a Macintosh? Do I need to purchase a diskette that is soft sectored/hard sectored for Mac to use it on models with both 1.44" and 400/800k floppies?

Edited February 7, 2021 by bluejay

[krslam]

Well, it's not hard formatted, but those 1440K diskettes are probably high density media, whereas your 800K Mac probably wants double density disks.  Because of differing magnetic properties and particle sizes, HD media will frequently fail or will lose data quickly when used on DD drives.

[bluejay]

Obviously I won't be using the 1.44mb diskettes on my 800k Mac, but I was asking if they'd work on a Mac with a 1.44mb drive or a Superdrive. Same goes for IBM formatted 720k diskettes; will they work on a 800k Mac with a reformat?

[Krebizfan]

Formatted at the factory. Yes, a format on the Mac is all that is necessary to make the disk work. 

 

The high density 3.5" disk is soft sectored. The layout is the same for IBM and Mac: 80 tracks per side of 18 sectors of 512 bytes each. Only the high level details of the file system will be different. 

 

Should you desire to make any 400K or 800K disks, I recommend finding some double density disks. Most* of the disks are identical to the IBM 720K disks but the resulting format will look completely different. The GCR Mac format seems to have been much more susceptible to failure if the wrong type of disk is used.

 

* Sony's initial design for the 3.5" disk used different materials than the DD disks that were made after the standard was ratified. It is very unlikely to find a Sony disk from 1982 or 1983 but if you do find one, send it to someone with the HP 3.5" or first batch Sony 3.5" drive. Besides a different cookie, the early disks lacks the spring loaded shutter so it makes the most sense to reserve those disks for drives that can't open the shutter. Sorry, a bit of trivia. 

[krslam]

Oops, guess I misread your post.  Yes, IBM HD media can be reformatted to work on MAC HD drives, and IMB DD media can be reformatted to work on DD drives.

[bluejay]

Thanks everyone for the enlightening me. I suppose I won't be purposely trying to hunt down diskettes that are actually advertised to work on the Mac, as if I understand correctly, any diskette will work with a reformat as long as it's the correct density.

[wierd_w]

Pretty much.  Hilariously, even a PC's floppy controller can produce a mac formatted floppy. (ARDI Executor, and FUSION PC emulator both had capabilities to do this) This is of course, with the HUUUUUUGE caveat that the PC floppy controller will never, ever, in a million years, be able to read or write GCR., and thus will never be able to make an 800k floppy.

 

 

But still-- To be further educational:  Hard sectoring was a thing that was done with 8in and 5.25" diskettes. On a soft-sectored disk, there is a single hole used to track a full rotation of the disk cookie. On a hard sectored disk, there are multiple such holes.

 

 

These are read using an optical pickup through a tiny punched window in the disk sleeve.

 

 

 

On a 3.5" diskette, there is no mechanism to track a full revolution of the disk cookie (in the diskette itself). Instead, there is a small magnet affixed to the side of the drive motor that spins the cookie, which is picked up by a coil winding.  When the disk is spun, this is registered by the drive's electronics.

 

 

As such, all 3.5" diskettes are technically 'soft sectored'.

 

 

[MrMaddog]

Techinically you could reformat a High Density disk as a Double Density by covering up the square hole (opposite side of the read/write tab).  Just stick a floppy in a Mac's drive and it'll ask you if you want to Initialize (format) the disk.

 

But that's not really a good idea in the long term since High Density disks use a thinner material and can get worn out quicker in DD drives, so that's more of a last minute thing untill you can get DD disks.

 

And the pre-formated disks were sold in office supply stores BITD so PC users wouldn't have to use the format DOS command, but they can be reformated for any computer...

[bluejay]

Yep, since floppies are so cheap I can buy a few 720k diskettes. I only have 2 1.44mb diskettes, so the last thing I wanna do is ruin one.

[carlsson]

My personal experience is that MFM formatted disks (PC) generally work very badly when reformatted as GCR (in my case Amiga and C64 on respective media type). The exact same batch of disks but never formatted on a PC work fine though. I suppose a bulk eraser would be useful to wipe out all traces of a MFM format before you do any form of GCR format (just like the older Macs use). YMMV but I'm not the only person to have experienced problems about this in the past.

[jhd]

 

I have gone the other way with no issues -- many years ago I bought a big package of Mac software at a flea market that was actually cheaper than purchasing the equivalent number of blank floppies. I reformatted each disk on the PC, and used them happily thereafter. 

 

I am reasonably certain that these were DD (720K) rather than HD (1.4M) media. 

Edited February 8, 2021 by jhd
Fixed a typo

[carlsson]

Yeah. For whichever reason I believe that MFM is more rigid in its formatting than various GCR schemes are so reusing an Apple/Mac or C64/Amiga floppy on a PC would probably not cause any trouble, only the other way around unless properly erased first.

[krslam]

Don't know if this is true or not, but I heard that whatever equipment was used to pre-format 5.25" PC disks used a stronger magnetic field so the relatively weak heads of Commodore and other home computers couldn't overcome it sufficiently to produce a new format. Bulk erasing was recommended before reformatting.  Wasn't really an MFM vs GCR thing.

[carlsson]

Could be, but I experienced it with factory unformatted disks that first would be used in a run of the mill PC with drives, then reused on both 1541 and Amiga drives and in both cases, read and write errors would build up much faster than on a fresh disk of the same pack that never touched a PC drive, let it be 5.25" DD or 3.5" DD. But quite possibly the drive mechanisms in regular PCs often had stronger magnets than the drives used in other brands as well. Hard to tell unless one take a "PC type" drive and modifies it to be used on another system.

[bluejay]

I had trouble formatting 5.25" floppies that were formatted on a DOS computer on an Apple DuoDisk, but not on a 1571. So I suppose what drive the floppy is being formatted also matters.

[wierd_w]

The phenomenon was well documented back in the day.

 

The suggestion was to bulk-erase the floppies, so that the media was randomized again. Apparently, the data signatures from GCR floppy sectoring were very difficult for the MFM formatting process to flatten (magnetically), and this lead to all manner of problems. (and vice-versa.)

 

 

These days, since I lack a good bulk erase wand, instead I have an ingenious plastic clip to hold a neodymium disk magnet in a dremel tool's bit retainer, and spin it around at high speeds.  Works OK for floppy media at least.

[carlsson]

5 hours ago, bluejay said:

I had trouble formatting 5.25" floppies that were formatted on a DOS computer on an Apple DuoDisk, but not on a 1571.

Good point. Just the other year, I believe Robin Harbron on 8-bit Show and Tell (or perhaps it was someone else) demonstrated how he was able to format 5.25" HD floppies on his 1571 and write files to them, though it was unclear for how long the files would be readable due to the stronger coercivity. Generally it is known that HD media can't be used on DD drives and certainly all 1541 drives would fail, but apparently the 1571 is stronger (and also supports MFM through Big Blue Reader). The same can be said about 3.5" HD floppies used on the Amiga etc. Many people did back in the day with varying degree of success but it would seem the difference in coercivity between 3.5" DD and HD is less than it is on the 5.25" disks so the chance is higher that it will work for a while.

[carlsson]

I don't know if the Macs in the original question have strong or weak drives, i.e. if the 1.44 MB floppy disks actually would be possible to use as 400/800K for a short while as indicated above. In an emergency with the intent to backup it soon after, it might work but not ideal if you intend to keep data readable for any longer period of time.

[bluejay]

I bought 5 used 720k diskettes off ebay for relatively cheap. I can use a few for the Mac and a few for PC, or perhaps something else entirely.

 

I have a USB floppy drive that claims to be Macintosh compatible. If even regular PC drives can write Mac format HD diskettes, I assume this is just for marketing purposes. Speaking of which, how come PC drives can write Mac format? I've heard of people using WinImage to write Mac diskettes on a PC, but I have no idea how this is possible. Also, how does file system and directory structure relate to the format of the drive?

Edited February 10, 2021 by bluejay

[wierd_w]

I know that old school NEC PC drives were able to do it, for limited periods. (do not try for archival, just for shuttling files, or getting an old system bootable and able to use a serial transfer cable)

 

Some brands of diskette worked better in this role than others. IIRC, the sony disks were worse than iMation disks.  Whatever kind of disk AOL was shipped on, worked quite well when reformatted as low density with tape over the hole.

 

The difference between 360k and 1.2mb diskettes was much too great though. Even attempting it, as I recall, would give you a track zero bad error right out of the gate on brand new media.

 

 

The PC and Mac 1.44mb capacities had the same "Sector marking and layout", but had different file systems stored on those sectors.  On the PC, you had the MBR on sector 0, track 0, and then the first copy of the FAT on the sector right after that.  On Mac HFS disks, it was significantly different with the HFS volume descriptor and pals at the top of the disk.

 

The PC programs were able to write raw sectors to the diskette, and so could write the data structures Macs expected to find.  Macs could do the same thing, which is how PCExchange worked to allow Dos formatted diskettes to be read, written, and created on classic macs with a 1.44mb drive.

 

 

Edited February 10, 2021 by wierd_w

[bluejay]

5 hours ago, carlsson said:

I don't know if the Macs in the original question have strong or weak drives, i.e. if the 1.44 MB floppy disks actually would be possible to use as 400/800K for a short while as indicated above. In an emergency with the intent to backup it soon after, it might work but not ideal if you intend to keep data readable for any longer period of time.

The one in my 512ke was weak. Failed to format a HD diskette that had been formatted in FAT12 before. Not sure about 400k or superdrives.

[carlsson]

It would seems that the measurements of 300 Oe and 600 Oe are nominal. I found an article on Wikipedia with ranges of values, whether those mostly refer to the media or the drives. I mean if 3.5" DD can range up to 600-670 Oe and 3.5" HD begin at 700 Oe, the gap isn't that big.

https://en.wikipedia.org/wiki/Disk_density

[godslabrat]

On 2/8/2021 at 4:33 AM, MrMaddog said:

Techinically you could reformat a High Density disk as a Double Density by covering up the square hole (opposite side of the read/write tab).  Just stick a floppy in a Mac's drive and it'll ask you if you want to Initialize (format) the disk.

 

But that's not really a good idea in the long term since High Density disks use a thinner material and can get worn out quicker in DD drives, so that's more of a last minute thing untill you can get DD disks.

 

And the pre-formated disks were sold in office supply stores BITD so PC users wouldn't have to use the format DOS command, but they can be reformated for any computer...

Yep.  I remember very common computer advice in the floppy era was "Don't forget, 'Formatted' and 'Preformatted' mean the same thing!"  

[Krebizfan]

3 hours ago, carlsson said:

It would seems that the measurements of 300 Oe and 600 Oe are nominal. I found an article on Wikipedia with ranges of values, whether those mostly refer to the media or the drives. I mean if 3.5" DD can range up to 600-670 Oe and 3.5" HD begin at 700 Oe, the gap isn't that big.

https://en.wikipedia.org/wiki/Disk_density

The Sony 3.5" design originally used disks of 500 Oersted which could explain some of the problems with high density disks. The standard 3.5" double density disks using basically the 5.25" high density disk material were already out of spec for the drive and the 3.5" high density disks were even further out of spec. 

[0078265317]

There was a utility to use pc disks on mac back in the day.

 

https://macintoshgarden.org/apps/pc-exchange

 

https://en.m.wikipedia.org/wiki/PC_Exchange

 

https://www.macintoshrepository.org/722-pc-exchange