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Nearly everywhere it's written that it's not possible.. But why? Why can't I dump a GPT/MBR partition table in the first sector? Basically dump a disk layout with sector size 2048...

Now I'm sure something of this type is possible, but of course no OS will recognise it.. So the question is, why not? What's so hard in a partition table? What's the technical reason behind zero support for partitioning an optical disc?

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    Let's say you do, and Windows, for example, mounts your partitioned optical disk into a E: and an F: drive. You might be tempted to access data from both of those at once, which will be excruciatingly slow on any optical media. Seek times on optical media are terrible ("Whereas a typical hard disk will have an average seek time less than 15 milliseconds, a fast CD-ROM drive can use tenths of a second for seeks." - tldp.org/LDP/sag/html/cdrom.html)
    – LawrenceC
    Commented Jun 5, 2014 at 16:15
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    DVD's have a similar thing called sessions. But DVD-RAM maybe could be treated like a flash drive, just slower but water-resistant and longer lasting.
    – neverMind9
    Commented May 16, 2018 at 15:42

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There may be two main reasons why partitioning isn't a well supported feature on optical media:

  • Optical media was at the beginning small (in comparison with HDD's).
  • Optical media was read-only. This later evolved due to easier access to consumer-level disk burners and the advent of RW technology.

Nowadays, there are much better solutions such as pen drives or even portable HDD. Not everyone has a Blu-Ray reader and not everyone wants to purchase a RW DVD. As such, in what regards optical media, partitioning was never demanded enough for it to happen.

I do have to point out the answer Rod Smith gave to a similar question, which I'm now quoting:

There are exceptions to this rule, though. Some Mac discs are written with a partition table and HFS or HFS+ instead of or in addition to ISO-9660. Such discs use the Apple Partition Map (APM) partition table. Some Linux distributions' installer discs use ISO-9660 that coexists with a partition table, but the intent here is to support different media in differnt ways -- when the image is burned to a CD-R or DVD, it appears to be a partitionless ISO-9660 disc; but when it's written to a USB flash drive, it appears to be a partitioned hard disk. This trickery works because of gaps in various data structures and the different sector sizes used on optical media (2048 bytes) vs. hard disks and USB flash drives (512 bytes). Both of these examples (Mac discs and Linux installation discs) are hackish extensions to the standards of ISO-9660, MBR partitions, and so on.

As you can see, it isn't technically impossible to do, but where it's done it's to provide additional support that couldn't be done in another way.

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    I'm not sure... I had a 260MB hard disk, about 10 years ago... from about 10 years before that. CDs started out at 700MB, and were not so small, relative to Hard Disks, until recently.
    – Milind R
    Commented Jan 21, 2014 at 12:10
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    @MilindR I think the read-only part was more significant.
    – jiggunjer
    Commented Jan 7, 2016 at 9:57
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It is quite easy to "partition" a DVD if you are creating the DVD on a Linux system. If you do "partition" the DVD, it will present itself to the OS as two or more separate DVD drives.

There are numerous ways to do this. For example, you can use the -eltorito-alt-boot option to mkisofs. This is what I use to create my UEFI Rescue DVD which contains a 32-bit and a 64-bit set of tools along with both the EFI and UEFI shells.

Oh, and the relevant specification is Mount Fuji v8.

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The iso9660 standard covers the cdrom specs and since partitions are not part of the specs nobody ever wrote a driver to handle them. No existing driver would support your changes to the file system, and all the programmers I know would not violated the specification.

Changing the driver now would not only mean adding a sector in the being, but changing the whole code base to accommodate the logic behind partitions. Lets pretend you wrote such a driver and made ISO's like that, they nobody else could read the ISO of the CD since everyone else has drivers that follow the specs. By the time you submitted your changes to ISO standards committee, got them to look at and go through the whole approval process would take years. However, they would probably not approve it since all modern hardware is design around the original specs.

The original thinking was probably who would want to partition such a tiny amount of space. They probably look at how much work it would take to develop,write, and test the code and said too much work to meet what ever deadlines they had.

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    Its not even the small amount of space. Blu-ray didn't do it either. My guess its because it would be really really slow..
    – Ramhound
    Commented Jan 19, 2014 at 1:19
  • @Ramhound Why would it be any slower than what it is already?
    – Milind R
    Commented Jan 21, 2014 at 12:11
  • @MilindR - I don't consider the read speeds to be slow. You have to understand how data is organized on a optical disk to understand the reason it would be slower.
    – Ramhound
    Commented Jan 21, 2014 at 12:14
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    Yes it would be a bit of work, but the specs are already screwed up when it comes to booting. Blu-Rays are pretty huge. GPT is a pretty generic table that'll fit anywhere. Isn't it time for a revision standard for DVDs, and Blu-Ray Discs?
    – Milind R
    Commented Jan 21, 2014 at 12:27
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    @Ramhound Would love to read and understand.. Any references/links to learn the nitty-gritties?
    – Milind R
    Commented Jan 21, 2014 at 12:29

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