Flipping your Disk (1981) | Hacker News Reader

Flipping your Disk (1981)

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There were custom tools for punching this hole in the exact right place, but you could also just freehand it. https://content.spiceworksstatic.com/service.community/p/pos...

The really cool trick on an Apple ][ was eeking out an extra 14% storage by modifying your drive to use 40 tracks instead of 35. Everything was designed to work with 40 track disks but for some reason the standard Apple ][ disk drive had a piece of metal physically preventing the disk arm from moving past track 35. You could bend / cut that out of the way and get 40 tracks. Even more if you hacked your software and trusted the disk media beyond track 40. But that was dodgy, up to track 40 was mostly safe. Except it broke a few copy protection schemes that would slam the disk arm all the way to the outside and expect that to be track 35.

I used a similar trick to get 1.68MB on a 1.44MB floppy. the extra 240KB really made a big difference in boot disks.

0: https://en.wikipedia.org/wiki/Distribution_Media_Format

I just used a pair of scissors.

I typed in and saved a disk editor program so I could use it to modify the directory information and skip one of the directory blocks. That's where I hid my secret stuff. And put an invisible control character in the name of the disk editor . My poor 8th grade teacher was none the wiser.

Yep, I had one of these back in the C64 era. It was called a "notcher".

I guess this was one of the most essential tool backs in the days of our peer-to-peer file-sharing networks ;-)

I used to do this all the time back in the day. I also used to buy floppies in bulk from some mail order catalog and re-sell them at a profit from my high school locker.

At the risk of showing my age, I did that in business school. There was a period when you could buy floppies in bulk and pricing was maybe 10-20% what they were by ones or twos in the campus store.

Someone else started this first but the floppies they were selling were crap so...

This was also a period when I earned money working in the school's computer lab to help students and there was more than one occasion where a student had their semester of work on a floppy and they bent it or otherwise made it difficult to read though I could usually get most of their info off.

Same here. I get the feeling this was a pretty common hobby. I would also pre-format them and charge a little extra. If you could afford to buy a batch of a thousand or so unformatted single sided floppies, doubling their capacity and formatting them, you could make some pocket change.

how many kids had computers? when I was in HS I was using 3.5" floppy and there were only a handful of us that had computers...

They didn't necessarily have computers, but they used computers.

Only a handful had computers, but there were enough who used the school computers to make it worthwhile. I didn't own my own computer until I was out of college.

I saw the author's name (MG Sieg) and thought it was MG Siegler (TechCrunch, now at Google Ventures: https://en.wikipedia.org/wiki/M._G._Siegler). MG Siegler was born just a few months after this article was published in 1981, so unless he was publishing in-utero, it was a different person.

And you can use a 3,5" floppy as single/double density if you cover the hole on the left (opposite the write-protection hole).

It's not supposed to work, but I've had a floppy like this for years and it reads fine.

Using a HD 3.5" floppy as a DD one is fine, however doing the reverse won't end well :)

It's actually not fine. I don't understand the chemistry but using an HD disk in a DD drive will appear to work, but the data will not be written "strongly" and will "fade" after a short time, becoming unreadable.

I think the trick to that is to reformat it multiple times. a DD drive has a lower intensity magnetic field, reformating it a couple times gets rid of the high intensity preformat on the HD disk.

I have several old synths with DD drives, and I've been using HD floppies with them for ~30 years without any problem. Late HD floppies were crap (whatever the mode), but old HD floppies formatted as DD back in the early 90s still work perfectly fine. I have several hundreds of these. Some having been used hundreds of times. Some I still use weekly.

It’s coercivity of the magnetic medium. HD disks have higher coercivity than DD which means higher write current is needed to put phase transitions down on the magnetic medium when recording. There are also some differences with track widths which complicates things further if you try to reformat from HD to DD without first degaussing.

For 3.5” disks the difference is small enough that you only tend to run into problems if you format a disk as HD in an HD drive then try to reformat and reuse it in a DD drive as DD without degaussing first (because the DD drive won’t be able to fully remove traces of the previous HD signal).

For 5.25” though the difference in coercivity is quite a lot bigger and even using freshly degaussed HD discs in a DD/SD drive will very likely lead to problems quite quickly.

Ah the memories. It turns out that Elephants do forget, especially on the second side.

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

http://blog.modernmechanix.com/remember-elephant-memory-syst...

https://www.youtube.com/watch?v=TDPbBO8jUA4

Fond memories! Eventually did the same on my C64 floppies, but only after having destroyed quite a few disks using my mom's blunt, giant scissors.

Used a soldering iron on my 3.5" disks, with a scalpel to take care of the excess plastic. Can't remember why I didn't use a drill, but I suspect drilling ran a bigger risk of particles getting inside.

I did drilling :) worked fine if I recall correctly. You had to spin fast, so it does not crack open the case. Memories indeed...

Punching a hold also made the 5.25 disk read/write instead of read only. Games and other software would often come with a "master disk" with no hole punched, and direct you to make a duplicate (or set of duplicates) that you would play off and save to.

Why weren't floppy disks sold this way to begin with? Some sort of economy of scale type thing?

There were floppies sold as double-sided and they came at a premium price: Before the floppy would be sold, it had to be verified at the factory and having both sides of the media functional was harder than just one side.

To expand: Early on there might've been some differences in the media rated for double sided disks, but by the time the floppy disk was a consumer item they were all using "good enough" media, and you could hole punch any SS disc to use the other side in an SS drive.

Few cared much really because the double sided drives were clearly the next one you were going to buy even if you hadn't got one yet. And then it wouldn't matter.

A fun trick with some combinations of drive and system involved having a disk that could be read differently when flipped, in a double sided drive. It wasn't viable large scale but crazy people having fun with stupid floppy tricks might produce a few occasionally and hand them around.

(Involved halving or less the sector counts and abusing alignment to interleave one side's sectors beside the others. If you wanted to be evil there were further refinements in what you could make the system report was there that wasn't)

I remember being told this was actually a myth. The manufacturers claimed this to be the case, but the problem was that different systems' drives actually used different sides of the disk, so the disk manufacturers had to verify both sides anyway.

Newer floppy drives had heads on both sides, you didn't need to flip the floppy and single write protection hole were used for both sides.

When you flip the floppy over the media rotates the other way. Supposedly the inside of the jacket had a fabric coating who's purpose was to catch fragments of media falling off during use. If you spin the media the other way those fragments come back off and gunge up the head. Or so the story goes.

Also of course there were real double-sided drives that used both sides of the media (with two heads). Vendors expected users to use those and pay extra.

Source: punched many a hole in Pet floppies back in the day.

I have a fabric brush that works on that principle, such that I have to take care when using it left-handed instead of right-handed as the direction changes and instead of removing lint from my garment it puts all the accumulated lint back on if I run it the wrong way.

But this is almost certainly not the case with the floppy disk fabric. Virtually every piece of Apple software sold on floppy that needed more than 1 disk side used the flip-side of the disk, making disk-flipping and running the disk "backward" not only common but necessary almost every time you used the computer.

There was indeed a fabric coating in most floppies, but in my experience taking them apart I never found any material that looked directional.

https://upload.wikimedia.org/wikipedia/commons/thumb/2/21/8-...

Pro tip: Don't try to punch an extra timing hole.

You can, if you are careful. The method is to indicate the position of the new index hole on both sides of the envelope with your template, and carefully insert the 'anvil' part of a hole punch through the large centre hole and between the active magnetic disk and the envelope. Punch the index hole on one side of the envelope then repeat the performance with the other side of the envelope.

I found that it was very rare for my 'flippies' to be unusable in my Z80 CP/M computer of the time.

Of course when we were able to afford those new-fangled double-sided drives, the whole incentive to make 'flippies' disappeared overnight.

It was easy enough to replace the notch-reading-switch with a toggle switch on the front of the drive, and optionally wire an LED in series. Then you could write-enable without a notch, and write-protect despite one. Like the mainframe disk drives!

Hmm, using a hole puncher is a pretty clever idea. If I had thought of that, instead of crudely sawing off a notch with scissors, maybe my success rate would have been higher. ;)

You can also punch holes in 3.5-inch double-density disks to attempt to turn them into high-density disks. :)

There actually existed hole punchers specifically for floppy disks. You lined them up to the corner of the floppy, and they'd punch a square hole at the proper location.

I recently found a large stash of these and gave them away at VCFMW. Then I found more in my basement...

I'll trade you one for my mouse roller cleaner, I'll even chuck in a mouse mat, and an AOL disc.

I must have been spoiled I thought those were really common. Every computer I used had one sitting nearby.

Good old Wikipedia have some more info, filed under flippy disk

https://en.wikipedia.org/wiki/Floppy_disk_variants#Flippy_di...

NOW you tell me???? It would be nice to know in the 80s when I had my Amstrad PC 1512!

If this is news, I’m officially old.

Good times.

What about the fact the timing hole was on the wrong side? Wouldn't that have affected the hole reader since it would never be able to read through the disk OR was there a reader on the other side

> The APPLE DISK is different than most other drives because it ignores the timing hole, using the motor and ‘soft’ timing techniques instead.

I don't know about every machine from that era but neither the C64 or the AppleII used the timing hole, relying on special signals on each track to identify the start of sectors.

Atari didn't need it either. The 1771 (or 2793 I think) floppy controller chip (a standard chip for IBM formatted floppies) does need the index pulse for the write track command for formatting. But the signal is just connected to a GPIO (I think on the 1050 drive this was fed by a timer).

This saves money, eliminating the need for the index pulse LED and photo transistor.

Reads never need the index pulse on soft sector floppies. Each sector has a header with the sector number and an "address mark" (a unique data pattern) used to detect the beginning of each sector and track.

Hmm, except the index pulse may have been used for a timeout if I remember correctly.

Correct. The C64 would just step the motor to the first track -1 and that is the reason for the head banging you got, as well as for the crappy alignment issues.

Didn't even need a notcher. I just used a pair of scissors.

I did it with an exacto knife. Some of that 5.25 inch floppy material was a little tough.

In some magazines they advertised a special hole punch with some alignment guides to do this, but it seemed expensive.

Most boxes of disks included stickers to recover the existing notch to write protect your disks too...

When I was a kid, I made an alignment tool out of cardboard, and later plastic from old whipped cream containers.

Yup, I made my alignment tool from a floppy disk sleeve. Made it easy to mark the location with a pencil, and then go in with the hole-punch to get it exactly right.

I just used a different disk to measure the depth and a Stanley knife with a fresh blade tip.

Get all nostelgic for those good old days when you messed around with the hardware.

Hole puncher made them perfect

I never ever had a problem on the other side.

There should be a (1981) in the title.

For posterity, but also curiosity.

"Make your 5.25" floppy double sided by punching a notch" hardly needs to be qualified with (1981).

Maybe some younger views will be less shocked by not knowing what's a floppy.

The joke I've seen: "someone made a 3d printing of a save icon!"

It still works.

Yup. It's there now.

Add 1981 =)

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