measurement of what? dimensions?

Assuming you are meaning "physical" measurement, it's really given in the name:

8" diskettes are exactly 8" square
5.25" diskettes are exactly 5-1/4 inches square

3.5: diskettes are slightly off - not exactly square - IIRC: about 3.5" x 3.7"

To find more exact information in the internet - look for <drive-type> diskette size - ie: 5.25" diskette size

If you're talking about capacity - this varies with exact format. Lots of information about this is included in my ImageDisk documentation/help.

DaveDDS wrote on 2026-06-06, 09:42:

Assuming you are meaning "physical" measurement, it's really given in the name: […]
Show full quote

Assuming you are meaning "physical" measurement, it's really given in the name:

8" diskettes are exactly 8" square
5.25" diskettes are exactly 5-1/4 inches square

3.5: diskettes are slightly off - not exactly square - IIRC: about 3.5" x 3.7"

To find more exact information in the internet - look for <drive-type> diskette size - ie: 5.25" diskette size

If you're talking about capacity - this varies with exact format. Lots of information about this is included in my ImageDisk documentation/help.

https://news.ycombinator.com/item?id=18833744 I tried ECMA but they do not having the files anymore.. I am planned to using this as a keycard because magnetic can destroy it, password-card, old well defined item, and because it is bigger than memorystick.. I having found something partially: https://www.micropolis.com/support/kb/3.5-inch-floppy-disk and https://www.micropolis.com/support/kb/5.25-inch-floppy-disk. Now I have found!! To all users, checking this attachment.

Qwseyvnd wrote on 2026-06-12, 11:44:

DaveDDS wrote on 2026-06-06, 09:42:

Assuming you are meaning "physical" measurement, it's really given in the name: […]
Show full quote

Assuming you are meaning "physical" measurement, it's really given in the name:

8" diskettes are exactly 8" square
5.25" diskettes are exactly 5-1/4 inches square

3.5: diskettes are slightly off - not exactly square - IIRC: about 3.5" x 3.7"

To find more exact information in the internet - look for <drive-type> diskette size - ie: 5.25" diskette size

If you're talking about capacity - this varies with exact format. Lots of information about this is included in my ImageDisk documentation/help.

https://news.ycombinator.com/item?id=18833744 I tried ECMA but they do not having the files anymore.. I am planned to using this as a keycard because magnetic can destroy it, password-card, old well defined item, and because it is bigger than memorystick.. I having found something partially: https://www.micropolis.com/support/kb/3.5-inch-floppy-disk and https://www.micropolis.com/support/kb/5.25-inch-floppy-disk. Now I have found!! To all users, checking this attachment.

The ECMA files can still be found on the Internet Archive ... https://web.archive.org/web/20180412001255/ht … ds/Standard.htm

Not sure exactly what you mean by "use as keycard" - I would think the obvious way would be to use a drive and store a few encryptes sectors on it (you could make them completely unique - unlilke normal sectors if you want to prevent it from being copyable)

If you want to make something special to read it like a card swipe, you would need to access the media slot - you might be able to read/write a few 10s of bits through the jacket ... but either way would have to prevent or account for the possibility of thr media layer to rotate.

Unlikely to find general details or consistancy at this level - best to pick a brand and measure as needed (and hope manufacuring process doesn't change)

DaveDDS wrote on 2026-06-12, 15:49:

Not sure exactly what you mean by "use as keycard" - I would think the obvious way would be to use a drive and store a few encryptes sectors on it (you could make them completely unique - unlilke normal sectors if you want to prevent it from being copyable)

If you want to make something special to read it like a card swipe, you would need to access the media slot - you might be able to read/write a few 10s of bits through the jacket ... but either way would have to prevent or account for the possibility of thr media layer to rotate.

Unlikely to find general details or consistancy at this level - best to pick a brand and measure as needed (and hope manufacuring process doesn't change)

Hmm... Okay, I understanding your opinion. I thinking for example microcontroller at media slot floppy drive so I do not need external common computer. Nowadays the microcontroller has a lot of integrated functions that before need a lot logic chips.