Do you mean which systems only used 3.5" floppies for the OS install disks?

I don't believe OP knows exactly what he means. Mostly because of mixing in the same sentence 80s computers with BASIC/TOS in ROM, CD-ROMs and 3" drives. This thread has the potential to start a nice discussion, but not like this, sorry.

I have a Commodore 1581 drive, which is a 3.5 inch 720k drive for the commodore systems.

cyclone3d wrote:

Do you mean which systems only used 3.5" floppies for the OS install disks?

yes! I know DOS did, I remember it well.

Er, just about everybody did until the early 1990s...

It has nothing to do with OS, and everything to do with hardware. Generally, 3.5" floppies were media of choice prior to ubiquity of CD-ROMs due to highest capacity. Only legacy systems lacked them.

dnewhous wrote:

cyclone3d wrote:

Do you mean which systems only used 3.5" floppies for the OS install disks?

yes! I know DOS did, I remember it well.

MS-DOS did not ship exclusively on 3.5in disks. Far from it. The first several versions of MS-DOS were shipped solely on 5.25in disks, and several more versions shipped on both 5.25in and 3.5in disks with the option to choose depending on what kind of drive your system had. In fact, if I recall correctly, MS-DOS 6.0 in the early 90s was the first version to not have an available option for 5.25in installation media, by which point the MS-DOS line was already about 10 years old.

Those that used were many.... This includes those, but not all that I have listed here below.

- Atari ST line.
- Atari Falcon.
- Amiga's (all of them).
- Commodore65 (it's a prototype, yet still)
- Apricot computers.
- Apple Macintosh.
- Apple Lisa.
- Different types of PC's.

As I said. There are way more computers and platforms than those I have listed.

EDIT:
As the 3.5 inch was invented around 1980, then you might want to continue searching this site, for machines from 1980 and newer.

dnewhous wrote:

cyclone3d wrote:

Do you mean which systems only used 3.5" floppies for the OS install disks?

yes! I know DOS did, I remember it well.

DOS also came on 5.25"

You could get up to Windows 95 and NT 4.0 on 3.5" floppies, but they were available on CD as well.

The Acorn Archimedes I used in school in the very late 80s to early 90s used 3.5".

The 3.5" floppy disk was created by Sony in 1981, though at first it was single sided/single density and held only 160 KiB. Later (1982), double sided/double density disks appeared which held 720 KiB.

In 1982, Hitachi, Panasonic and others introduced the 3" compact floppy disk (CF-2), that later got picked up by Amstrad and used in many of their computers. These were double sided and could hold about 360 KiB.

So in 1982-4 there were two "compact floppy" formats to choose from.