Read this postings from Alan Reeve:
diomond2.rom: Diamond GOS 3.0 ROM

From: areeve@mindspring.com (Alan Reeve)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Diamond OS
Date: Wed, 04 Nov 1998 14:27:55 GMT
Organization: MindSpring Enterprises
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Ok...the GOS 3.0 ROM is in the binaries newsgroup and the file is
called DIAMOND2.ROM so don't think it's the 2.0 ROM. That's the just
name on my Atari archive CD-R.

Also, keep in mind that you need the original Diamond GOS super cart
with its PLA chip to use this image. It will do you no good with a
standard cartridge.

And for those that don't know what Diamond is...it's a programmable
GUI environment created around 1988 for the Atari 8-bits that offering
moveable windows, mouse support, and all of that type of stuff.
Unfortunately there weren't too many apps made to take advantage of it
so the programmable aspect really didn't end up helping too much.
Reeve Software did release a Paint, Write, and News Station for it (I
think we released a Diamond News Station?), as well as a developer's
kit. Anyhow...hope the 3.0 ROM helps...I'm an emulation fanatic and I
certainly appreciate what 'Yogi' did a couple years ago with
maintaining the big Atari 8-bit archive (I contributed many files
myself) and I love to see this stuff kept alive for the history books.

  - Alan

From: areeve@mindspring.com (Alan Reeve)
Newsgroups: comp.sys.atari.8bit
Subject: Here's the Diamond GOS 3.0 ROM - Diamond2.rom (0/1)
Date: Wed, 04 Nov 1998 00:42:26 GMT
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Here's the final Diamond GOS ROM image...precisely 64k...burn it to a
27512 and you'll be set. As usually I take no responsibility for any
side effects in doing this. You're free to distribute it...add it to
Atari archives...make emulators that work with it...whatever... Sorry
if anyone is bothers with binaries in this newsgroup, but it's only
64k.
  - Alan