Only one Primary partition on a HD should be marked "active", and
Disk Management will only mark one Primary partition "active".
When it marks a Primary partition "active", it will unmark the existing
"active" Primary partition. But I have seen an Extended partition
marked "active" by a 3rd party utility without any bad consequences.
The only significance of "active" is that the HD's Master Boot Record
will search the partition table at boot time, and it will pass control to the
boot sector on the Primary partition that it finds to be marked "active".
In that "active" Primary partition, the boot sector expects to find ntldr,
boot.ini, and ntdetect.com (the "boot files"). Once ntldr starts up, it
will load the OS from whatever file and from whatever partition in the
system that the selected entry in boot.ini indicates.
*TimDaniels*
"b11_" asked: