I've just been messing around with imaging some original DEC VAX/VMS CDs (original distributions of the operating system). I was expecting that making ISO files of the original CDs, and then burning those ISOs back to blank CD-R disks on a PC would require an optical drive that has a block-size jumper. I assumed this because I thought that PC drives expect media to have a block size of 2048 bytes, and VAX machines expect media to have a block size of 512 bytes.
Anyhow, I'm a little confused because I've just been using a SATA DVD R/W drive in a cheap modern-ish desktop system, and to my surprise I was able to successfully make an ISO of a VAX/VMS 6.1 CD in that drive (and "install" VMS from that ISO in a VAX simulator in SIMH) and then write out the ISO in the same drive to a blank CD-R disk (which I then used to successfully install VMS 6.1 on a real MicroVAX 3100 Model 90).
What I don't understand is why this worked. Have modern optical drives become sufficiently intelligent that they can figure out (or fudge?) block size, or has block size always been irrelevant to reading and writing ISO images to/from CDs (perhaps it's only relevant to accessing files within the ISO image)?
(the imaging was done under Ubuntu 14.04 using command line tools. "dd" was used to read the original CD, and "wodim" was used to write the ISO out to a blank disk. I've documented the process in some detail here -> http://avitech.com.au/?p=605).
Anyhow, I'm a little confused because I've just been using a SATA DVD R/W drive in a cheap modern-ish desktop system, and to my surprise I was able to successfully make an ISO of a VAX/VMS 6.1 CD in that drive (and "install" VMS from that ISO in a VAX simulator in SIMH) and then write out the ISO in the same drive to a blank CD-R disk (which I then used to successfully install VMS 6.1 on a real MicroVAX 3100 Model 90).
What I don't understand is why this worked. Have modern optical drives become sufficiently intelligent that they can figure out (or fudge?) block size, or has block size always been irrelevant to reading and writing ISO images to/from CDs (perhaps it's only relevant to accessing files within the ISO image)?
(the imaging was done under Ubuntu 14.04 using command line tools. "dd" was used to read the original CD, and "wodim" was used to write the ISO out to a blank disk. I've documented the process in some detail here -> http://avitech.com.au/?p=605).