1.2/1.44 all the way by that point. My 1.2mb DOS 5 setup floppies at least date to 1991.

1.2MB for 5.25" floppies. I am not aware that 5.25" disks with 720k were ever used on the PC. IBM went from 360k straight to 1.2MB when they introduced the AT in the mid 80s. The only disk type to use 720k were 3.5" drives introduced on early PS/2 systems IIRC.

I'm pretty sure there was a 720kb 5.25" format, but it was some non standard quad density thing. A few systems in the early 80s had them, but 1.2mb drives are not compatible with those disks. I think the 720kb drives can at least read the 360kb disks however.

The 1.44mb drive was pretty much the standard during the 486 era, but some of the very first 486s in 1990 were equipped with a single 1.2mb drive. 486s sometimes were equipped with both 1.44 and 1.2mb drives, but dropping the 1.2mb drive really became a thing in late 1992 or early 1993. My 486DX-33 from September 1992 came with a 1.44mb drive, and there were times when I considered adding a 1.2mb drive, but it was only really useful for installing 286 era software.

1.2MB 5.25" drives were almost 2 times more expensive compared to 3.5" 1.44MB floppy drives also during 1996 ! (Estonia). Also those 5.25" drives worked just like lottery and were unlucky deal. It was hard to get a second hand working 1.2MB drive, most were out of calibration, only 360kB and 1.44MB drives were in abundance, which had no such calibration problem. At last I had acquitance 4 of those drives. 3 were out of calibration.

there were such formatting programs which allowed to use non-standard formats on floppys (800.com for example) thus forexample formatting which were also more than 720kB. In fact I tried that and many strange floppys which couldnot be formatted at 1.2MB were usable as 720kB. The same program was used on all sorts of drives then.

3.5" floppys were worst at the same time -- brand new first Sony 1.44MB floppy which I bought in my life got the bad sector just after 2 copying, which was not the same case with no-name floppys. Also some verbatim floppys -- beautiful to look but impractical sometimes. 😁

Even in 1988 286 pc I bought came with both 1.44Mb and 1.2Mb floppy drives and a 40Mb hard drive

I don't really remember 5.25" 720kB standard in PC world. However in early nineties 720kB (5.25" ) floppy drive was quite popular addon for Amiga (at least in Poland), because floppies were cheaper.
As far as I know these 720kB drives were modded 1.2MB ones (I did this modification by myself once).

My WYSE system from 1986 has both a 1.2MB 5.25in drive, as well as a 1.44MB 3.5in drive. The 3.5in drive admittedly could have been installed at a later date, but the 1.2MB drive is definitely factory-original. I'd say once you get past about 1987 or so, you'd be hard-pressed to find solely 360K drives in all but the cheapest of computers.

The only major exception I can think of off the top of my head would be the Apple II line, which IIRC never supported high-density 5.25in disks as mainstream even late in its life (The Apple IIe was still for sale new as late as 1993). Instead, Apple jumped directly from double-density 5.25in to 3.5in disks with the IIc Plus and IIgs, while keeping the 5.25in support at double-density. I imagine peculiarities of the Woz drive design probably played a part in this decision, although their fumbling with the ill-fated Twiggy drive could have also played a role in souring their mood towards supporting newer 5.25in media as well (The failure of Twiggy is what made Apple one of the first mainstream adopters of 3.5in disks after all). 😜

Anonymous Coward wrote:

I'm pretty sure there was a 720kb 5.25" format, but it was some non standard quad density thing. A few systems in the early 80s had them, but 1.2mb drives are not compatible with those disks. I think the 720kb drives can at least read the 360kb disks however.

The 1.44mb drive was pretty much the standard during the 486 era, but some of the very first 486s in 1990 were equipped with a single 1.2mb drive. 486s sometimes were equipped with both 1.44 and 1.2mb drives, but dropping the 1.2mb drive really became a thing in late 1992 or early 1993. My 486DX-33 from September 1992 came with a 1.44mb drive, and there were times when I considered adding a 1.2mb drive, but it was only really useful for installing 286 era software.

Wasn't that for the apricot PC's from the 80's with some of the first 3.5 disks?

0kool wrote:

I need to know what was The most popular and widespread floppy disk density in the DX-DX2 era...

This is quite a lot of years. In 1990 there were new XTs still getting sold, obviously with DD drives. In 1994, although not popular yet, DX4s were available. Another world.
I'd just go by this rule of thumb: XT=DD, AT=HD.

BSA Starfire wrote:

Wasn't that for the apricot PC's from the 80's with some of the first 3.5 disks?

I started highschool in 1985 and that was the year our computer lab with "brand new PCs" had been opened. Those brand new PC's were Apricot F1s with 3.5" 1.44MB drives. I'm sure about that since I still had the Nashua brand HD floppy from that time until recently 🤣

I owned my first PC in 1992 (April or May I think) and it came with both 5.25" 1.2MB and 3.5" 1.44MB drives, because I prefered and ordered it that way. I needed to exchange data with the old Unisys 386 workstations in the department which had only 5.25" drives. Otherwise it was pretty uncommon for common folk buying a PC with 5.25" drive (or retailers encouraging the same) even in 1992, even around where I live.

These Unisys 386 workstations had Unisys branded user manuals for MS-DOS 4.01 and Windows/386 2.1, so they were either from very early 1991 or (most probably) 88-89 (I believe they were Pw800 series which were definately pre 1991) .