|The drive letters assigned to hard drive partitions by the operating system are not "written in stone" - they're logical drive letters. When you have more than one operating system on a computer, the logical drive letters for a particular partition on a hard drive are not necessarily the same in each of the operating systems. |
When you install XP, whether or not C is assigned to the partition Windows is installed on depends on what other partitions XP's Setup detects that have already been assigned drive letters when Setup is run. If there are no such other partitions, XP's Setup uses C for the partition XP's Windows is installed on. If there are other such partitions, XP's Setup uses the next available drive letter alphabetically, NOT C.
You can see which drive letter XP is using for it's partition Windows was installed on in System Information.
(If you installed XP second without wiping the whole drive of partitions Windows 7 installed, that's NOT C !)
I haven't installed Windows 7 yet, but I have installed Vista, and the vast majority of things about Vista work the same way as for Windows 7.
I have installed both Vista Premium and XP MCE 2005 on the same computer.
I installed XP MCE first, Vista Premium second.
Things I found -
In my case, both XP MCE and Vista see the partition their own Windows version is installed on as C .
(There were no partitions on that drive, and no other hard drives with existing partitions connected, when I ran XP's Setup.)
Apparently, when you install Vista, it uses C for the partition Vista's Windows is installed on, regardless of which other partitions have already been assigned drive letters when Setup is run, if XP was installed previously.
(I installed it on the second partition of the same hard drive, and there were already other partitions that had been assigned drive letters by XP on the same drive, as well as partitions on another hard drive. )
Vista can see the partition XP's Windows is installed on, and all the partitions, but XP cannot see the partition Vista's Windows is installed on (it sees all the other partitions; I made those with XP).
If you dual boot Vista and XP, ALL the System Restore restore points in Vista are DELETED, EVERY TIME you boot XP.
There are Microsoft suggested workarounds, but the Bit locker feature is not available to you if you don't have the Ultimate or Business versions of Vista, and the other one may not work in all circumstances.
The only sure way you can get around that, if you don't have the Ultimate or Business versions of Vista, is to use a third party boot manager program that can hide the Vista partition (it's Windows was installed on) from XP while booting XP, and that also supports Vista's ACPI features properly.
In my case, I then installed and used BootIt! NG, and from then on, booting XP did and does not delete the restore points in Vista.
(The same probably applies to dual booting XP , or 2000 ?, and Windows 7.)
"In disk manager the other partitions are shown as disk0 unallocated space."
That doesn't make sense.
In Disk Management, the 320gb drive (it's smaller binary size) is shown as Drive0 . The partitions on the drive are shown in the box beside that.
If you are using an operating system on the same drive, it's not possible for all of Drive0 to have unallocated space.
"Now the problem is that my computer do not shows other drive letters."
Window's Setup defaults to making only one partition on a hard drive if the hard drive is blank and has no data such as when it's brand new, or if you wipe the hard drive of existing data (delete all existing partitions) and make a new partition. If you want to make more than one partition on the drive, do not accept the default size - change that to the size you want for the partition Windows is going to be installed on, and you can software partition and format other partitions in Disk Management in Windows later after Setup has finished.
In XP you can't change the size of the partition Windows was installed on after Setup has been run with what is built into Windows without deleting that partition first and losing all it's data, but you can use third party "partition Manipulation" programs to do that.
In Vista, probably Windows 7, you CAN change the size of the partition Windows was installed on with what's built into Windows. At the very least you can make the Windows partition smaller - if the Windows partition was not taking up the entire space on the hard drive, you can also make it larger.
If you make the partition Vista's (and probably Windows7's) Windows was installed on smaller, there will then be unallocated space on the hard drive, or in any case if there is unallocated space on the drive in Vista ( and probably Windows7), (and) you can software partition and format the un-allocated space in Disk Management, then that formatted space will have one or more drive letters.