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How FDISK and the Operating System Create and Allocate 131
first hard drive has an extended partition on it, the second hard
drive will take the primary partition’s D: drive letter. This moves all
the drive letters in the first hard drive’s extended partition up at
least one drive letter.
This example lists a drive with C:, D:, and E: as the drive letters (D:
and E: were in the extended partition). Table 4.26 indicates what
happens if a second drive is added with a primary partition on it.
Table 4.26 Drive Letter Changes Caused by Addition of Second
Drive with Primary Partition
Original Drive New Drive Letter(s)
Partition Letter(s) (First After Adding
Drive Type Order Drive Only) Second Drive
1st Primary 1st C: C:
2nd Primary 2nd — D:
1st Extended 3rd D:, E: E:, F:
This principle extends to third and fourth physical drives as well:
The primary partitions on each drive get their drive letters first, followed
by logical DOS drives in the extended partitions.
How can you avoid the problem of changing drive letters? If you’re
installing an additional hard drive (not a replacement), remember
that it can’t be a bootable drive. If it can’t be bootable, there’s no
reason to make it a primary partition. FDISK will enable you to create
an extended partition using 100% of the space on any drive.
Table 4.27 shows the same example used in Table 4.25 with the second
drive installed as an extended partition.
Table 4.27 Drive Letter Allocations After the Addition of a
Second Drive with an Extended Partition Only
Original Drive New Drive Letter(s)
Partition Letter(s) (First After Adding
Drive Type Order Drive Only) Second Drive
1st Primary 1st C: C:
1st Extended 2nd D:, E: D:, E:
2nd Extended 3rd — F:
This operating system behavior also explains why some of the first
computers with IDE-based (ATAPI) Iomega Zip drives identified the
Zip drive as D:, with a single 2.5GB or larger hard disk identified as
C: and E:—the Zip drive was treated as the second hard drive with
a primary partition.