Is 5.5 Bigger Than 5.25

[Priamo Gregory]

Answersand comments to Why were 5.25" floppy drives cheaper than 8"? suggest some reasons why floppy disks moved from 8" to 5.25"; basically it seems the smaller size reduced engineering difficulty and thus cost in a number of ways.

On the contrary, beyond a certain point, miniaturization becomes difficult and adds cost. With late seventies technology, 5.25" was the optimum balance between the cost of a larger mechanism and the cost of a smaller one.

As it turns out, smaller was indeed cheaper, but that would've been too much of a leap into the unknown at the time, for an industry that as yet had no experience with disks smaller than eight inches.

The only difference was in size, a linear shrink with a factor of about 1.5 (*1), which means the needed surface and thus size shrunk in half (*2). All without any basic change, just relative minor adaptations. For example to manufacture the floppies only the punch to cut out the magnetic foil with its corresponding holes (same for sleeves) and folding brackets closing a disk sleeve and so on had to be made. So just new tools to be installed on existing machinery. To produce 3.5" ones, new steps, different materials and different handling had to be developed - quite a large investment, especially compared to retooling.

It's a bit like the Tick part of the often cited Tick-Tock strategy Intel follows for CPUs. A shrink of an existing design just in scale, not design or function. The following Tock was then again a step of design changes (*3).

Some comments (for example jcarons) asked why not going smaller, like 3.5, but keeping technology the same. Beside all the technical reasons regarding recording (like density), it's much about mechanical reliability. For example due thinner materials the medium gets more sensitive to damage - and more so, a smaller hole in the middle reduces reliability for centering while increasing stress on the material (due a reduced lever) at the same time.

This isn't anything theoretical, as Mitsumi tried exactly this with their 2.8" variation. Beside having meager capacity of 64 KiB per side, they were extremely unreliable. For Nintendo's Famicom-Disk they created a redesigned version borrowing the centering mechanism (in plastic) as well as a hard case, making it match the setup of a 3.5" drive - sans the slider, keeping the need for sleeves.

A 2005 interview with Don Massaro, vice-president ofengineering and manufacturing, and George Sollman, product manager, both of Shugart Associates, lists the design constraints that resulted in the world's first 5 inch floppy drive, the Shugart SA 400 minifloppy:

Massaro: [Dr. An Wang of Wang Laboratories] said..."I want to come out with a much lower end word processor. It has to be much lower cost and I can't afford to pay you $200 for your 8" floppy, I need a $100 floppy."

Sollman: We looked at all the various tape drives that were out there. We said we had to replace them and that this is the size and we said, "How big can you make the diskette?" It turned out to be 5 1/4.

So they wanted a disk drive that was (1) cheaper than an 8 inch floppy drive, (2) the same size as a tape drive (or they wanted a floppy disk to be the same size as a tape cartridge, the interview is unclear on this point), and (3) within that last constraint, they wanted the diskette to be as big as possible, probably to optimize capacity.

Drive size: 8" drives as part of an integrated system really limits your form factor choices. You can have the drives integrated with the monitor and everything else, like the TRS-80 Model II and then it doesn't seem so bad. But if you are making a smaller machine - e.g., Northstar Horizon, or a machine where the floppy drives are separate - e.g., Apple II, Atari 800, then 5.25" gives you a lot more options on how/where to place the drives.

However, jumping in the 1970s, to a smaller size would have resulted in either significantly reduced capacity (as already noted, if using the same track density and other parameters as 8" and initial 5.25" drives) and/or significantly increased costs due to more expensive (at the time) integration of electronic circuitry. So 5.25" gave the desired advantages - space, weight, cost - without going "too far".

When 3.5" did become a real thing, it came with a significant change - the hard plastic case. This brought in a new advantage of durability. At the same time, the technology for the necessary circuitry had advanced by that time enough to provide a higher capacity (720k and up) without a higher cost. This was also the era where the rest of the computer had shrunk enough to start producing laptops, where the size advantage of a 3.5" drive was critical. In the late 1970s and early 1980s, a typical motherboard the size of today's (or even 1990s) laptop motherboards, didn't include floppy drive controller, hard drive controller, video card, etc. So there was no practical reason to make the drives that small.

In order to read/write information from the disk the read/write head has to be positioned over the correct area. Then the head itself needs to either sense changes in magnetic flux (read) or alter the magnetic flux (write).

So each track needs to be wide enough that the stepper motor can reliably position the head over it. Unlike a hard drive where it's always the same stepper motor, floppy disks have to work with the motors in many different drives so the tolerances have to be a lot lower.

5.25" was as small as the could go while keeping the technology somewhat affordable and reliable at the time. Later Sony improved tracking and better motors were available, so 3.5" disks became commercially viable.

Marcell Jnosi patented the 3" "micro casette disk" in 1974, if the Hungarian bureaucracy wouldn't been in the way, there wouldn't have been any 5.25" disk as there was no need. Although the first working prototype was only made in 1979 that was because the factory director thought this didn't fit the COMECON plans. My grandfather, who worked there in the seventies claimed Jrosi was close and the factory was ready by 1975 (he gave the date as my birth and I was born in 1975) to manufacture it. (He alas passed away in 1985, the year I learned BASIC on a ZX Spectrum my parents smuggled into the country and I saw some Commodore 64 machines using floppies and that's when he told me how Hungary had a better floppy ready a decade ago.)

At the time, there wasn't a need for a smaller form factor. Reducing drive bay size from 8" format to 5.25" format was enough to allow companies to transition from wide and/or tall rack mount type cabinets to desktop like frames and 5.25" drive bays became a standard. Most current desktops still include some 5.25" drive bays.

Trivia - for hard drives, part of what drove the 3.5" form factor was the fact that mounting a 3.5" hard drive in a 5.25" adapter frame provided enough shock tolerance to allow it to be used in the early Compaq "luggable" computers.

I have a number of 5.25" floppies for the BBC Micro which haven't been used since the 90s. I recently got my BBC Micro and Watford Electronics floppy drive down from the loft/attic, set it up and tried the disks. Unfortunately my floppy drive had fallen apart internally and no longer reads any of the disks. I tried fixing it (the drive head had come apart) but to no avail. There was no noticeable mould damage to the disks.

How did you store them over the past decade or so? Where they in a cool, not-so-humid area away from direct sunlight? If so, I bet you have a decent chance of recovering the data if you can find a working drive.

Interesting question. Those 5.25 disks are generally similar in quality of the newer 3.5 disks. And 3.5 disks are also considered antique since most new computers don't have a floppy drive anymore. Anyway, I have an USB-based 3.5 floppy drive which works just fine.

Looking at my own floppy disk collection from two decades ago, I noticed that most of them have had some damage due to years of not-using-them. Mostly bad sectors or just random blanks. These disks use a magnetized surface and this is slowly leaking away. (Faster if stored in sunlight or near large magnets.) I was able to still get data from some of those disks, though. Maybe about 20% of my disks are still completely readable. I did store them in a dark place, well-protected in a floppy case.

For disks with damaged data you might want to use a disk drive that's more sensitive than regular floppy disks. This would be special forensic hardware though, and thus a bit expensive if you're even able to find one. This disk could then be used to revive the data on those disks so you can transfer them to some other medium. But considering the value of your data, I don't expect this to be worth the trouble.

There will be another problem, though. Are those floppies used for an MS-DOS computer or for some other operating system? They might not be using the FAT file system but some other file system which Windows won't be able to read.

Formatting those floppies and using them as extra data storage isn't practical either, since they're likely to contain 320 or 360 kilobytes of data, depending on the number of sectors on those disks. Back then, this wasn't even enough to store the MS-DOS setup! It's no surprise that the 3.5 disk quickly replaced it, since the plastic cover made them tougher and the disks could have 720 KB or even 1440 KB, depending on disk quality. (Although you could transform a 720 KB floppy to an 1440 KB floppy by drilling a hole in the right place.)

They should not be dead, though. They might be blank, but not dead. If you format them all, I guess that 95% will be reusable. But you're not interested in getting extra disk space but the content of those disks. Well, it is possible to get part of them back, depending on how much you're willing to do and pay for the data recovery. You just have to consider if it's really worth the trouble. That's just between you and the data on those disks.

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