Bootable GPT partitions

[mikro]

Here: https://www.hddriver.net/en/exchange.html one can read an interesting note that "HDDRIVER will also be able to boot from these partitions".

I presume the byte-swapping option still must be enabled for standard Atari IDE interfaces (e.g. Falcon), right? I.e. there will be a performance hit.

[uweseimet]

Yes, byte-swapping and the partition scheme are two completely unrelated things. When using GPT partitions everything that is not directly related to the partition scheme stays like it is. For byte-swapping this means that it is needed in the same scenarios where you need it with the MBR partition scheme.

Regarding bootable partitions in general, when you have more than 4 partitions on a drive, with the MBR scheme there can only be 3 primary partitions you can install a bootable hard disk driver on. The 4th primary "partition" is the XGM one, which cannot be bootable.
With a GPT and more than 4 partitions on a drive you can always install a bootable hard disk driver on the first 4 partitions. This is because with a GPT there is no such thing like a secondary partition.
In practice you hardly profit from this, of course, because most likely you anyway install the hard disk driver on drive C:, which is usually the first partition. I say "usually", because with a GPT you can have partitions of different operating systems on the same drive, i.e. the first partition does not necessarily have to be a TOS-compatible partition. An OS/driver typically just ignores the GPT partition types it does not know.

[mikro]

Noted, thanks for the detailed reply.

[uweseimet]

GPT support for HDDRUTIL (HDDRIVER has already supported the GPT scheme for several years) is available now. HDDRIVER 12.50 has been released today.

[francois]

Here: https://www.hddriver.net/en/exchange.html one can read an interesting note that "HDDRIVER will also be able to boot from these partitions".

I presume the byte-swapping option still must be enabled for standard Atari IDE interfaces (e.g. Falcon), right? I.e. there will be a performance hit.

In my case, I was able to boot on a Falcon IDE drive with GPT partitions. However, I had to specifically make sure that byte-swapping is DISABLED.

At least with TOS 4.04. Maybe something like EmuTOS can boot on byte-swapped disks?

[uweseimet]

With release 2.41 the tools of the util-linux package, in particular fdisk, recognize TOS-compatible GPT partitions, which are also supported by HDDRIVER and HDDRUTIL:

Code: Select all

Device       Start     End Sectors   Size Type
/dev/sdh1       34  482841  482808 235,7M Atari TOS basic data
/dev/sdh2   482842  965617  482776 235,7M Atari TOS raw data (XHDI)

As usual, the new tools are going to be integrated into upcoming Linux distributions. Even old Linux versions or FreeBSD can use these partitions, without any special tools or kernel configuration.