Hard Disks and Partitions

How to partition, format, or wipe your hard drive

Before a hard disk can be used it must be partitioned and formatted.

Partitioning determines how many drives you will end up with, and how big they are. In the DOS/Windows world, this is done with a program called FDISK.EXE.

Formatting encodes the disk with the information necessary for data to be stored on it: the Master Boot Record and the File Allocation Tables. This is done with a program called FORMAT.COM.

You might think of the process as something like this: you have a very large piece of paper, which you decide to cut into 8.5" x 11" sheets (partitioning); then you add lines and margin rules to each sheet (formatting).

Physical vs Logical drives

Any hard disk may be partitioned as a single large drive, or split into two or more smaller drives. For example, a 10 gigabyte hard disk may be split into three: one 4G drive, and two 3G drives. They will appear as drives C:, D:, and E: (if you have a CD-ROM it will become drive F:). In this case, you have one physical hard disk (drive), but three logical drives. Sound simple enough? Too bad. It isn't always that way. If you have two hard disks, things get complicated (see below).

Primary and Extended Partitions

You must have a primary partition, which is normally the one the operating system (Windows) will boot from. The primary partition may use the entire disk, or only part of it. If the primary partition does not use the entire disk, then you can either leave the rest of the hard disk blank, or you can create an extended partition. The extended partition, in turn, can use up the rest of the hard disk or not, as you wish. So, after creating the primary and extended partitions, you then define logical drives within the extended partition. Finally, in order to be bootable, the primary partition must be made active. In summary, it's a four-step process:

1. Create the Primary partition,using as much of the hard disk as you wish
2. Make the Primary partition active (this doesn't have to be step 2)
3. Create an Extended partition, using as much of the remaining space as you wish (optional)
4. Create a Logical drive (or several), within the Extended partition

Why would I want to leave part of the hard disk blank?

In case you want to install another operating system, like Linux, or Windows NT, or something else, and make a dual boot machine. With NT and Linux, you need to install Windows 95/98 first.


One final warning, and I can't emphasize this enough: FDISK is a program that WIPES hard disks. EVERYTHING on the disk will be erased, and you will NEVER be able to get it back.

Starting with a new, blank hard disk

You will need a boot disk for your system (see how to create a boot disk)

With your computer off, insert the boot floppy into the floppy disk drive, and turn the machine on. When the machine boots, you will see a command prompt, like this:


Type "fdisk" (upper or lower case - it doesn't matter), and press Enter. You will see a screen with a lengthy and nerdy message (see Fig. 1), with a question, to which you answer Y or N; just make sure to choose Y. You will not see this message if you have a hard disk smaller than 512Mb.

Fig. 1

FDISK - initial screen


The next screen gives you a list of options:
Fig. 2


You want to select option 1. Create DOS partition or Logical DOS Drive.; then you will see the following screen:
Fig. 3


Again, you want to select option 1. Create Primary DOS Partition.

Next, you will be asked how big you want the Primary DOS Partition to be. You can specify it in either megabytes, or a percentage of the total disk space. Personally, I find it easier to use a percentage figure.

(simulated screen capture)
Create Primary DOS Partition

Current fixed disk drive: 1 

Total disk space is X* Mbytes (1 Mbyte = 1048576 bytes) 
Maximum space available for partition is X* Mbytes (100%) 

Enter partition size in Mbytes or percent of disk space (%) to 
create Primary DOS Partition..............................[X*] 

Press Esc to return to FDISK options 

Take the default option to create one partition with 100% of the available space.

You will then see a message at the bottom of the screen about "verifying drive integrity", and a number counting up from 0% to 100%

Then you will see a screen like this:


Create Primary DOS Partition



Partition Status Type Volume Label Mbytes System Usage
C:1 PriDOS 3565* UNKNOWN 34%

Primary DOS Partition Created

Press ESC to continue

What does this mean?

Partition C:1

That is, drive C:, partition 1.


Whether the partition is active or not; if it were active, there would be an "A" under "Status".


PriDOS means Primary DOS partition. Even in Windows 95/98, FDISK calls it a DOS partition.

Volume Label

This is just a name for the drive. You can give a drive a name, or not, as you wish (see FORMAT).


The size of the drive, in megabytes.


What type of File Allocation Table is on the drive. Since this drive is still unformatted, FDISK can't tell yet.


What percentage of total hard disk space this drive is occupying.

Making the Primary DOS partition active

Press Esc until you get back to the main menu (Fig. 2). Choose option 2, Set active partition. There will only be one partition available (C:1). Make it active, and press Esc again to return to the main menu.



If you survived partitioning your hard disk (and were successfull), using FORMAT will be easy.

After partitioning the hard drive, you must reboot the machine in order for the changes to take effect. You will then see the A: prompt again.

At the A:\> prompt, type:

format c:

You will be warned that this operation will erase all data on the drive, and are you SURE you want to proceed. As long as you are sure, type "Y".

When the format is complete, you will be asked if you want the drive to have a volume label, which is no more than a "name" for the drive. Type one if you wish, or leave it blank. You can always add or change the volume label later.

If you have successfully partitioned and formatted your hard disk, CONGRATULATIONS! You have just accomplished two things that very few computer users know how to do.

As I said at the beginning of this document, things get a little more complicated if you have two hard disks. That situation is covered in Part 10.


If you had wanted to create more than one partition, you could have chosen a size for your DOS partition and then created 2 partitions.  Much of this depends on your hard drive size.  After you create the Primary DOS partition with, for example, 50MB of space--you create an extended DOS partition that you may leave whole or further subdivide into logical drives.

Creating the Extended DOS Partition

At the main FDISK menu (Fig. 2):

1. Choose option 1, Create DOS partiton or Logical DOS drive.
2. Choose option 2, Create Extended DOS partition.

You now have a screen similar to when you created the Primary DOS partition; you are asked how many megabytes, or what percentage of the remaining hard disk space, is to be assigned to the extended DOS partition. If you accept the default (which is in megabytes), or specify 100%, ALL the remaining space on the disk will be assigned to the extended DOS partition.
NOTE: the percentages in this section represent the percentage of space in the Extended DOS Partition; this is NOT the percentage of total hard disk space. 


Since we want to assign all the remaining space to an extended DOS partition in this exercise, just press Enter. You will again see the "verifying drive integrity" message, then you will be asked to define logical drives in the extended partition (next).

Creating Logical Drives in the Extended DOS Partition

For the first drive, specify 50%; you will see a line appear at the top your screen, similar to what you saw when you created the primary DOS partition, showing drive D:, its type, size, etc.

Next, you can simply press Enter for the size of drive E:. Whatever the size is (it will be in Mbytes), that will be the other 50% of the extended DOS Partition.


Press Esc until you are back at the main FDISK menu (Fig. 2), and choose option 4. Display partition information, to check that everything is as you wish. Then, press Esc until you are back at the A:\> prompt, and re-boot the machine.  

You must format ALL of your partitions and Logical Drives