It's identical to IBM PC DOS 3.3 (circa 1987) except the two spaces after IBM are changed to MS -- dunno if that was done officially for some reason or someone hacked it in.

further down it says ibmdos.com

coolhaken wrote:

I have a game in .IMG format dumped by my friend. The OEM Operation System Name is mysterious for me. IBM PC DOS 3.3 ? MS-DOS 3. […]
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I have a game in .IMG format dumped by my friend.
The OEM Operation System Name is mysterious for me.
IBM PC DOS 3.3 ? MS-DOS 3.3 ?
Anyone know what is it ?

sshot-1.png

Floppy and hard disk images that have the IBMMS3.3 OEM signature within the first 16 bytes of the disk were formatted under IBM PC-DOS 3.3 (1987). Further down, you will see a IBMBIO.COM and IBMDOS.COM - those are files that are need to boot the OS.

ppgrainbow wrote:

Floppy and hard disk images that have the IBMMS3.3 OEM signature within the first 16 bytes of the disk were formatted under IBM PC-DOS 3.3 (1987). Further down, you will see a IBMBIO.COM and IBMDOS.COM - those are files that are need to boot the OS.

Thanks for your reply.
As you said, this OEM signature "IBM 3.3" is IBM PC-DOS 3.3 and "IBMMS3.3" is IBM PC-DOS 3.3, too.
They are all officially, right ?
Don't know what's the different between them ?

coolhaken wrote:

Thanks for your reply. As you said, this OEM signature "IBM 3.3" is IBM PC-DOS 3.3 and "IBMMS3.3" is IBM PC-DOS 3.3, too. They […]
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ppgrainbow wrote:

Floppy and hard disk images that have the IBMMS3.3 OEM signature within the first 16 bytes of the disk were formatted under IBM PC-DOS 3.3 (1987). Further down, you will see a IBMBIO.COM and IBMDOS.COM - those are files that are need to boot the OS.

Thanks for your reply.
As you said, this OEM signature "IBM 3.3" is IBM PC-DOS 3.3 and "IBMMS3.3" is IBM PC-DOS 3.3, too.
They are all officially, right ?

That's correct.

IBM did indeed licence MS-DOS from Microsoft, but that relationship was usually not mentioned explicitly in PC DOS itself (e.g. lots of "Licensed Material - Program Property of IBM" messages, but no mention of MS anywhere). So, the signature containing "MS" seems odd... I've never seen it on any English versions, at least.

Uhm, don't know if that's true, but wasn't PC-DOS 3.30 a bit ahead of its time ?
This site claims it was released before MS-DOS 3.30.

And I think it was also the first version to support 1.44MB floppies (MS-DOS 3.2 didn't),
extended partitions (early FAT16) and batch files.

Maybe that's the reason some things were still in an -uhm- "beta" stage..

Edit: Just checked, my copy of PC-DOS also has the "IBM 3.3" signature on its floppies (see morsel below).