A hard disk can have a maximum of 4 primary partitions – don't ask me why, I don't know. Apart from primary partitions a hard disk can also have what is known as an extended partition which inturn can hold a number of logical partitions – I believe the number is close to 15. The extended partitions are not real partitions like primary or logical partitions in that they don't store data but are actually containers for logical partitions which is where data is actually stored – as you can see it is uneccessarily complex. Thus in Windows C is a primary partition and if you used Windows Fdisk – Windows Fdisk will not make more than one primary partition to partition your hard disk – D is usually the first logical partition of the extended partition. E would be the second logical partition and so on. In Linux things are slightly different. The first primary partition is called /dev/hda1, the second primary partition /dev/hda2 upto the fourth which is /dev/hda4. Linux refers to the an extended partition as in the case of a disk with 1 primary and one extended partition as /dev/hda1 for the primary and /dev/hda2 for the extended. The logical partitions of the extended partitions are referred to as /dev/hda5, /dev/hda6 and so on. The second hard disk would be referred to as /dev/hdb, the third /dev/hdc (usually the cdrom drive if set as secondary master) and the fourth and last hard disk as /dev/hdd (last because the motherboard has place for a maximum of 4 IDE devices) SCSI devices are referred to as /dev/sda – thank god for that.