My workstation at work came with a 1.2g hard drive. After I figured out I could conserve space by using smaller partitions I began to wonder what I could do with some of the extra space. To make matters more interesting I usually use a second computer to test installs of software that I write for the company. I ended up asking myself, wouldn't it be more efficient if I had two Windows 95 setups on the same machine? How could it be done? It would also be nice to have a Windows 3.1 setup available for testing as well.

I thought about a Windows 95 dual boot setup. I figured it wouldn't be real efficient, besides it wouldn't help with the multiple Windows 95 setups. It occurred to me DOS supports up to 4 partitions (more if you use an extended partition). If I could create a 800mb partition for my primary development environment, a 200mb partition for Windows 95 testing, and a 200mb partition for Windows 3.1 testing it would be just what the doctor ordered.

Theory:

DOS supports up to four partitions to a drive. Each partition is marked with a type. DOS itself basically has only two types of partitions, a "Primary DOS" and an "Extended DOS". The "Primary DOS" partition is capable of being booted while the "Extended DOS" is not. The "Extended DOS" partition is capable of being further divided into as many sub-partitions as needed up to the total number of drive letters available (usually 23). Other partition types are used by alternate operating systems.

Windows 95b adds two other types of partitions. They are basically the same as the original DOS partition types but denote the use of the "Fat 32" file system.

When your system starts up it must determine which partition it should boot from. It does this by looking at the first drive on the first hard drive controller for an "Active" partition. You use FDISK to mark a partition as being "Active". FDISK only allows you to mark "Primary DOS" partitions or other operating systems partitions as being "Active".

During the startup of DOS or Windows 95 the system will assign drive letters to all "Primary DOS" and all sub-partitions within the "Extended DOS" partitions.

Problem:

In order for this strange idea to work you have to be able to make multiple "Primary DOS" partitions. The FDISK utility supplied with DOS or Windows 95 does not allow this, so you have to use some other partitioning software to do it. I used a program I wrote myself. You can do it with Windows NT and "Partition Magic" claims to be able to do it, but I have not tried it.

Once you have your system partitioned it's a matter of formatting the partitions with the desired operating systems. You can switch between partitions by using FDISK (or equivalents depending on operating system).

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Notes:

1. Partitioning is a potentially dangerous process!
2. Some versions of dos don't handle multiple Primary Dos partitions.
   • Dos versions 5.x and greater do.
   • Windows NT Does.
   • Novell DOS DOESN'T.
   • I haven't tried any other DOSes.
3. Windows NT's partitioning software will allow you to do this.
4. There are third party programs that make partitioning easier.