Paul,
VAX CD-ROMS generally are not ISO. ISO implies the ISO9660 file system, but many VAX CD
ROMS are in native VMS Files-11 format.
Some Windows utilities don't handle these so you need third party software to create
an image of these CD's.
Generally it has a .iso extension but as the content is not ISO9660 you can't mount it
on Windows or Linux.
There a couple of utilities that will convert arbitrary files to image files.
I tend to use CD Burner XP
https://cdburnerxp.se/en/download
but you need to click "More download options" and use the "without install
core" versions....
Dave
  -----Original Message-----
 From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of ben via cctalk
 Sent: 04 May 2019 19:39
 To: cctalk at 
classiccmp.org
 Subject: Re: Service for converting CD-ROMs into ISO files?
 On 5/4/2019 8:15 AM, Paul Koning via cctalk wrote:
 thought a CD-ROM (data CD) *is* an ISO image.  So I would expect all you
 need to do is make an image copy of the disk.  On Unix systems that's trivial,
 just use the "dd" command to copy /dev/whatever to myfile.iso.
        paul 
 Window users rejoice (until the next verion breaks something).
 
http://www.chrysocome.net/dd