On this page (http://www.pcguide.com/ref/hdd/file/struct_Partitions.htm) of Pcguide, i read The extended DOS partition system allows you to have up to 24 disk partitions in a single system

does that mean we can have 24 different file-systems on the same hdd ? :eek:

yeah i believe it does

Actually, no because some file systems are not limited to the 24 non-reserved letters of the alphabet (A & B, being the two reserved letters). So theoretically you can 24 DOS partions and number of non-DOS ones.

But, this is on a SYSTEM, not a hard drive. So while you can theoretically have more partitions than you could ever want on a hard drive, you would not be able to do the same on a separate hard drive on the same system.

Ok, lets use the linux filesystem ext2 as an example.

It uses a labeling scheme of hd*/n, with the * being a letter that represents a physical device and n representing the partition number. So you could have 26 physical drives, each with almost any number of partitions. Those partitons could be formatted into any filesystem you want.

Using DOS there are 24 non-reserved letters, these can be either devices or partitons on a device. With DOS (which means the FAT family), you are limited to 4 primary partitions and the rest would need to be extended/logical for a total of 24. Using MS fdisk limits you to 1 promary partition per physical drive, but other partitioning tools can create more than one primary per physical drive (also some abolish the 4 primary limit).

So, theoretcally, with a 200GB drive, you could assign 100 partitions (assigned by percentage as opposed to fixed size) using a combination of tools and format each one as a separate file system. With carefully assigning what goes where you can even have many of them bootable (some file sytesm need to be locatated in the first 1024 cylandeers ot be bootable).

With IDE devices you are limited in the physical drives as 2 per controller channel or 2 per IRQ (each channel requires an IRQ). With SCSI devices you are limited by the number you can daisy chain per controller and free IRQs (one for each controller). Usually this is something like 15 devices per controller.

While it is theoretically possible to set up such a complicated structure as 100 partitions on a single drive, the practicalities of managing such a setup would test the limits of sanity. And with using just the available MS tools it would be nearly impossible. Third party and native tools for alternate OSs would be needed.

so that means no of file-systems possible = no of partitions on a single hdd.... forget aba the devices.

Probably, but some do need to be in the first 1024 cylanders to be bootable, and a couple need to be there to work at all...I think FAT12 is one.

got it :) thx.

Good for you, learning all about disks and file-systems.

Some day you might run into people who use these terms differently.

They may use terms like "logical-partitions" or volumes.......

Especially when discussing multi-OS PC configurations......