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Recently there has been some confusion about which kind of 3.5 inch floppy to use. Is that high density, double sided, double density, I'm confused...
To complicate matters Apple has migrated to a new floppy disk drive technology. This new "Floppy Disk High Density" (FDHD), or "SuperDrive", technology is incorporated into the SE/30, IIx, IIcx, IIci and Portable. It is also available as an upgrade for existing SE and MAC II owners. This drive allows you to use 1.44MB Mac disks and allows you to read/write IBM DOS 720K and 1.44MB disks.
It is important to understand that the Mac now has three types of disk formats that you can use.This excludes the two types of formats that IBM can use (more on that later).
The 8OOK drives found in the regular SEs and older MAC IIs can read, write and format disks either at 400K or 800K bytes. The SuperDrives found in the SE/30 and IIcx when using "High Density Media" can read, write and format disks at 1.44MBytes, along with ability to still use 400K or 800K disks.
Moral of the story check your disks.
To met this demand the disk manufactures of course make at least 3 types of disks. But how do you tell what you've got?
Here are some hints.
If the disk has no writing on it, take a another hint it's cheap media, no written claims on the disk imply no warranty about its quality. Consider switching to disks which make some sort of written claim.
Look for:
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"Single Sided" A 400K disk, don't use at 800K, consider getting other disks
"Double Density" An 800K disk, but could be a 400K disk, look for "Double Sided" to confirm its 800K nature.
"Double Sided" An 800K disk, but could be an 1.44MB disk, look for the "HD" symbol to confirm its 1.44MB nature.
"135 TPI" An 800K disk (Usually, watch for the Single Sided mark)
1MB Implies it's an 800K disk.
"High Density"/HD A real 1.44MB disk, use only at 1.44MB in the IIcx, SE/30 or portable, never format it at 800K
Great hint, this seems to be a symbol which has been accepted by most vendors to denote a 1.44MB capable disk. Again use only at 1.44MB, in 1.44MB drives
2MB Implies disk can be formatted up to 2MB, thus 1.44MB is OK, however confirm this via the HD symbol
Physical? Yes, High Density media is physically different, look for a hole in the casing directly across from the Write Protect Hole. In fact you need this hole for the disk to work correctly in a MAC (more on this below).
Color? Red, Blue, cream? Forget color, it no longer implies anything.
As you can see much effort has gone into identifying High Density media and there is a good reason for this. Both Apple and IBM do not recommend using this High Density Media in older 8OOK disk drives. Data saved to high-density media using 4OOK and 8OOK formats could be unreliable and may be lost later. This is a proven fact since people within ESSO have experienced the thrill of losing all the data on their floppies.
Since Apple introduced this technology sometime after it was available they were able to take advantage of the physical differences between the media. Thus on an SE/30 you can only format High Density disks at 1.44MB, no other option is available, and they always assume that the disk will always be 1.44MB. So if you use an older SE to format one of these disks at 800K you will find that SE/30 will not be able to read it, since the "hole" tells it to treat it as a 1.44MB disk.
With the PS/2, IBM for some reason did not follow the standard by checking for the extra "hole" therefore you can quite easly format a 720K/800K disk at 1.44MB. This disk may last a few months before you have problems, but if you attempt to read this disk on a MAC via Apple File Exchange or "DOS mounter", you will find that the MAC will refuse to accept it. The converse is true you can format a 1.44MB disk at 720K. This will cause you problems in the future and a MAC will yet again refuse to accept it.
If you use the correct type of disk in your machine at the correct density (800K/1.44MB) you better increase the probability of reading that disk some time in the future, and across technology platforms. Remember, if you make poor or uninformed choices about the disks and how you format them you may later regret it.