*TechNote*: Hard Drives #3 - Partitions and Logical Drives

[bellboy]

Partitions, logical drives and formatting
_________


People often get partitions and logical drives mixed up. Partitions and logical drives are set up with fdisk.

A logical drive is not a hard drive, but how a single hard drive can be assigned several drive letters. Logical drives are also called volumes.

The drive letters a: and b: are reserved for floppy drives and cannot be given to anything else.

For example, if you have a pc with windows 95 as an operating system and open my computer to see the following drive letters:

a: c: d:

The pc has one floppy drive (a:), a hard drive with a single partition (c:) and a cd-rom or dvd-rom (d:).

The partition which contains the operating system is defined as the active partition, and is also referred to as the primary partition.

If, on another windows 95 pc has the following drive letters:

a: c: d: e:

The pc has one floppy drive (a:), a primary/active partition (c:), an extended partition with one logical drive (d:) and one cd-rom or dvd-rom (e:).

The extended partition is sub-divided into logical drives. you can have one logical drive in your extended partition or up to a maximum of 23. Though if you do have 23 logical drives in your extended partition, you will not be allowed to have a cd-rom/dvd-rom or install any further hard drives as all your drive letters will have been allocated.

Partitions and logical drives must be set using fdisk before they can be formatted. Formatting is also called logical formatting.

The size of the volumes will be dictated by the format command. FAT volumes are a maximum size of 2gb and FAT32 volumes are a maximum size of 2tb (terabytes).

The DOS command lastdrive is required in the config.sys file is you are using dos on your pc, as the default number of logical drives is set to five. As a: and b: are reserved for floppy drives and therefore automatically set, and the first drive letter of a hard drive is c:, it means that e: will be the last volume seen by DOS. Anymore than three logical drives on a hard drive, or two logical drives if use a cd-rom that can be seen by dos, must have the lastdrive set in config.sys.