Gabhlan said:
Assuming Apple are going with BIOS instead of OperFirmware (as stated in the universal binary guide pdf Apple distributed), then how many partitions per disk can you have? As I understand things, in a standard BIOS a disk can only have a maximum of four partitions. Can anyone with experience of BIOS confirm or deny?
If true, that'd really suck... A standard OS X install on a blank disk yields three partitions already, (the partition table, OS9 drivers and the OS), meaning you could only have two other partitions on a disk (the OS9 driver partition won't be there I assume). I for one was hoping to be able to boot OS X, Windows XP, Linux and Zeta from different partitions on the same disk on a new Macintel PowerBook......
No one has appeared to answer this so I will....
The standard PC partitioning scheme is NOT defined by the BIOS. The BIOS itself has no clue what is on the hardrive and could care less how this data is laid out. Was does define the partitioning scheme is the standard that everyone has adhered to over the years. The only thing the BIOS does concerning data on the hardrisk is to start executing the first sector of the disk. Also known as the MBR, or Master Boot Record. It contains the partition table which defines the partitions on the disk. The MBR is where "boot loaders" for running multiple operating systems is placed. This is the nice little menu you get when you have multiple OSes installed. When you select a OS to boot, yet another jump happens. The partitions themselves contain what is know as a PBR or Partition Boot Loader. When you select a OS the code in the MBR jumps to the appropriate partition and starts executing its PBR. The PBR contains the OS specific code that actually starts booting the operating system. (in the case of a single OS like Windows XP, the MBR boot code simply jumps to the PBR of the Windows partition which then starts loading the actual OS)
OK, now that I have explained that...
The partitioning scheme itself was pretty much defined by Microsoft with the introduction of MS-DOS. It supported 4 partitions originally. When the IBM PC clones arrived and the market took off we got stuck with this layout. Changing it would have required major changes to DOS and most software. The partition limit eventually became a problem and Microsoft figured out a scheme to add addtional partitions while maintaining compatibility with older software. This scheme consisted of nesting addtional partitions inside one of the 4 main partitions.
The 4 main partitions from that point on where called "Primary" partitions. If you want more than 4 partitions you would change one of the Primary partitions into a "Extended" partition, and then inside of that you would create a "Logical" partition that would actually contain your data. When old software looked at the partition table they would ignore the "extended" partitions, Only newer software would recognize them.
The extended partition is nothing but a container to hold all of your logical partitions. You can only have ONE extended partition on a hardisk and that extended partition can contain up to 24 logical partitions.
This gives you a maximum of 27 partitions possible using the scheme. The 3 "primary" partitions and then the 24 logical partitions.
Microsoft, with the advent of Windows 2000, developed a new partitioning scheme know as Dynamic Volumes. It is completely different from the current scheme and only Windows 2000 and up can read them. (and I think Linux has some beta support for them as well) Its not used in the mainstream however and probably never will be.
But or course it remains to be seen if Apple will stick with the PC partitioning scheme. If they want to allow people to install other OSes on their hardware then they definately will have to. But otherwise they can design any scheme they want and still continue to use the ol' PC BIOS.
