As you may have noticed, sometimes I waste time gathering useless information. Today we’re going to look at write protect notches for floppy disks and other media.
The 8-inch floppy was unusual in that the drive was mounted vertically. You inserted the floppy with the label facing left. The write protect notch was at the top of the leading edge. If you put the floppy on a table with the label in the upper left, the leading edge would be the bottom edge, and the write protect notch would be on the left part of that bottom edge. The presence of a notch made the floppy write-protected, so you started with a write-enabled floppy, and if you wanted to protect it, you punched a notch at just the right spot.
If you placed a 5¼-inch floppy on a table with the label in the upper left, the leading edge would be the bottom edge, and the write-protect notch was on the right edge, near the top. When inserting the floppy into the drive, it would be on the left side near your hand. The presence of a notch made the floppy write-enabled. To protect it, you covered the notch with a sticker. So it was really a write-enable notch, not a write-protect notch.
The 3½-inch floppy had a write-protect hole in the upper right corner when you put the floppy on a table with the label in the upper left, leading edge at the bottom. An open hole made the floppy write-protected; a covered hole made it write-enabled. A sliding door on the underside of the floppy let you decide whether the hole was open or closed. Update: Corrected 2026-03-04.
The Iomega Bernoulli Box was a proprietary system that used cartridges for storage. If you put the cartridge flat on a table, the natural orientation was for the label to be at the bottom, with the leading edge at the top. There was a sliding switch on the bottom left corner to control whether the media was write-protected, but no hole. Instead, the switch had a ⊘ symbol on one side (not 🚫), indicating that moving the slider to that side would write-protect the cartridge.
The last media I used regularly from this era was the cassette tape. The write-protect notch was a recess in the upper left corner covered by a tab, and if the tab was broken, then the cassette was write-protected.
I’m amused that different media had different opinions as to whether the presence of a hole/notch/recess meant that the media was write-enabled or write-protected.
| Format | Position when on table | Hole means |
|---|---|---|
| 8-inch floppy | Bottom edge, left side | Read-only |
| 5¼-inch floppy | Right edge, top side | Writable |
| 3½-inch floppy | Top right corner | Read-only |
| Bernoulli cartridge | Bottom left corner | No hole! |
| Cassette tape | Top edge, left side | Read-only |
SD cards .. I think even the microSD form factor still has a notch, for readonly content.
Hmm.. do CD/DVD drives have some inherent ability, to distinguish between a readonly and a rewritable disc?
There's a quirk of history behind the floppy ones, too. The 8-inch floppy was initially not field-writable, and thus there wasn't a need for a read-only/writable marker - all 8-inch floppies were read-only by definition once they left IBM.
Then, field-writable drives came out. This created a need to determine whether a given disk ought to be read-only or not; the reason for deciding that a carefully cut hole meant "read-only" is, as far as I can find, lost to history.
For 5¼-inch drives, though, the decision that the hole means writable was very deliberate; this meant that you could manufacture read-only...
This is a such a classic example where a picture is worth so many more words. And would be so much more fun too. But the basic point that the standards were inconsistent is interesting nonetheless.
Some commonly used media that’s missing here: zip and jazz. I suspect they would have followed the 3.5 in standard…
Also, 3.5″ floppy disks also had a hole in the top-left corner to indicate that they were HD (High Density) and could hold 1.44MB of data. Without a hole, those were DD (Double Density) and could hold 720KB.
As a money-challenged college kid, we would go to the big box paper store and buy a box of 100 DD floppies, and then use a hot soldering iron to melt a hole in the plastic case to turn them into HD floppies, with a pretty good success rate given that the magnetic coating was different between the two types of disks.
The 3-inch Compact Floppy had two write-protect holes on the leading edge. I don’t remember which one affected each side, but those were definitely write-protect holes, and not write-enable holes.
Oh! SD cards (full size). These have a notch and a slider on the left side near the top (when placed on the table, label up, contacts down and away from you). When the notch is open, the card is writable; moving the slider over it write-protects it.
On VHS cassettes, it’s trailing edge, left side. When placed flat on a table, label up, spine facing you, the tab is on the spine, on the left. When the tab is intact, the cassette is write-enabled; you break it off to write-protect, same as audio cassettes.
The reason that 8″ floppy drives were usually vertical was, of course, that 8″ floppies were floppy: if you held them horizontally the far edge sagged significantly, and inserting them into a drive (or even a sleeve) in that orientation was difficult.
Worth noting that the 8” and 5.25” could be used upside-down, so you could add (or cover) a hole in a completely different location to write to the other side.
Writing to the other side was only possible when using double sided disks (standard from the early 80s) on single-sided drives (originating in the 70s). The Apple II and Commodore 64 were the most well known cases. In the PC, it was quite rare even in the 80s, as IBM switched to double-sided drives early on.
In these years I used an Apple IIc. When I took a new blank disk, the first thing I did was cutting the B-side notch, before I even formatted the A-side. I used regular scissors, so it was a bit risky. I never botched...
Of course if you were too hasty you may have cut into the inner disk…
For the hasty people you could purchase specific disk hole punchers. What a bliss, to get home with a new 10 pack of disks from the next town, punch holes and format them for later use.
I also did exactly this with the 1541 disk drive on my C64 in the ’80s. Felt great to get two disks for the price of one!
For 9-track tape: On the back side, insert a ~4″ diameter rubber ring into a groove. These “write enable” rings came in many pretty colors so they would stand out against the white tape reel.