Each hard-disk in your computer can store upto 4 logical drives. Usually only one PARTITION is defined, using all the disk space, and assigned the letter C:\.
On COMPAQ and other proprietry systems, a second DIAGNOSTIC PARTITION usually
exists. So be careful when creating new LOGICAL-DRIVES/PARTITIONS.
Under normal circumstances, each operating system, (OS), must reside on a PARTITION of its own, and a BOOT-MENU lets you select an OS. (Or, if so configured,
will automatically start the last loaded OS, unless you press key X, for the BOOT-MENU).
WINDOWS, when upgraded, may also allow you to BOOT the previous version from the
START-MENU, (Press F8 at start-up), if you saved the previous version. Note this is basically a compressed file, on the same PARTITION. (C:\).
You can't, as far as i am aware, RE-SIZE an NTFS PARTITION, (Used by NT/XP), so you must back up all your data, orl lose it when you create the PARTITIONS.
If you want to run two OS's, each OS will have to create its own PARTITON, before you can start the INSTALLATION. (Eg: DOS uses FDISK.EXE and XP uses PARTDISK to create a PARTITION).
The PARTITIONS don't have to be the same size, and it doesn't really matter in which order the PARTITIONS are created in. But you are better off creating the first PARTITION for the OS you are going to use most