Installer will fire up fdisk(8)

After a few instructions, the installer will fire up fdisk(8) and automatically print out your partitioning from the Master Boot Record. The top of fdisk’s output contains some basic disk geometry information.

Disk: wd0    geometry: 1 2438/ 2 255/3 63 [ 4 39166470 Sectors]

This line describes what fdisk(8) believes is the disk geometry in the number of cylinders, heads, and sectors a disk has. According to fdisk(8), this disk has 1 2438 cylinders (numbered 0 through 2,437), 255 heads (numbered 0 through 254), and 63 sectors per cylinder. If you compare this information to what the physical label on the hard drive says, it almost certainly won’t match. That’s all right — it’s just been translated. One interesting thing to note is that fdisk(8) reports that this hard drive has the same total number of sectors as every other tool reports, however.

A little beneath that, you get a table describing the MBR partitions themselves.

     Starting     Ending      LBA Info:
#: id  C  H  S -  C  H  S [    start:    size   ]
------------------------------------------------------------------------
* 1 0: 2 0B 3 0 4 1 5 1 - 6 891 7 254 8 63 [   63:   14329917 ] 9 Win95 FAT-32
    1:   00 0  0  0 -   0   0 0 [       0:     0 ] unused
    2:   00 0  0  0 -   0   0 0 [       0:     0 ] unused
    3:   00 0  0  0 -   0   0 0 [       0:     0 ] unused

This isn’t nearly as confusing as it looks at first glance. The first column gives the MBR partition number, between 0 and 3. We then see the 2 Partition ID. This is a unique hex number used to identify the type of file system on the partition. Partition ID 0x0B represents FAT32.

fdisk then prints the 2 cylinder, 3 head, and 5 sector where this partition begins. The first partition on this disk begins on cylinder 0, head 1, sector 1 — the beginning of the disk. ^[1]

The next three columns show the cylinder, head, and sector where this partition ends. Compare these numbers to the total number of cylinders, heads, and sectors in the drive. This disk has 2,438 cylinders, of which we are using 892. Within cylinder number 891, we are using up through head 254 (all of the heads) and  sector 63 (all of the sectors). This Windows partition completely fills the first 2,438 cylinders. We say that such a partition ends on a cylinder boundary. All of your partitions should begin and end on a cylinder boundary.

At the end of the line, we have the partition type in clear English. We could get this information by looking up partition ID 0x0B in a table, but it’s certainly convenient to print it here.

Finally, fdisk presents a command prompt.

fdisk: 1>

We want to create a new MBR partition, immediately following the existing FAT32 partition.