Using FDISK

Partitions are created, destroyed, and managed by a program usually called FDISK. Each operating system has its own version of FDISK, so be sure to use the correct one. If you’re now using DOS or are planning to use DOS, you must first repartition the DOS drive by using DOS’s FDISK. You later use the Linux version of fdisk to create the Linux partitions. If you’re using OS/2, you also need to use the OS/2 version of FDISK to prepare the OS/2 partitions.

Partition Requirements

First, you should plan what partitions you need. DOS requires a primary partition; Linux and OS/2 can reside in other partitions. If you’re using the OS/2 boot manager, which also works well with Linux, you must prepare for its use. You must also be aware that if you’re shrinking a current DOS partition to make room for Linux, not all of your files can be restored to the new, smaller DOS partition.

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NOTE:  You can access DOS partitions from Linux, thus moving, saving, and editing DOS files under Linux. But you can’t execute DOS programs under Linux.

Two experimental components of Linux allow you to emulate DOS under Linux and also install Linux under DOS. Both systems are still in the implementation stage and are, thus, more suited for Linux hackers. Also, one of the methods, UMSDOS, is incompatible with Red Hat, so you can’t use that method at all. You can find plenty of information on these topics in the Linux world.

• See “Running DOS Programs Under Linux,” p. 127

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Next, you should jot down the number of partitions you need and how much disk space to provide each with.

DOS Requirements

If you want to boot DOS, it must go in a primary partition. A bootable version of DOS doesn’t require much space—just enough for the system files, COMMAND.COM, CONFIG.SYS, and any driver files needed to start your system. For example, I provide a 5MB DOS partition on my first drive to boot DOS.

When DOS is loaded and running, you can access any of the other extended and logical drives on the system. Unfortunately, whereas Linux can access DOS files in a DOS partition, DOS can’t access Linux files in a Linux partition.

OS/2 Requirements

OS/2 versions 2.0 and later don’t need a primary partition. The OS/2 system can install and boot from an extended partition. Thus, you can install DOS on a primary partition and create an extended partition area for OS/2 and Linux. The space required for OS/2 is version- and feature-dependent; you should consult your OS/2 documentation for space requirements. You should also subtract 1MB from available space if you intend to use the OS/2 boot manager.

Linux Requirements

As explained earlier, Linux stores files on file systems, and these file systems can reside on different partitions, basically as safety precautions. Linux requires one partition for each file system. The next consideration is for a swap partition. Linux, like most operating systems that use disk space for memory (called a virtual memory configuration), needs a swap file or a swap partition to simulate physical memory using disk space. Linux typically uses a swap partition.

The size of the swap partition depends on the amount of physical RAM your system contains. A rule of thumb is to make your swap partition twice the size of your amount of RAM. Thus, if you have 8MB of RAM in your system, you should create a swap partition 16MB in size. If you have 4MB of RAM or less, you must activate a swap partition.

Linux swap partitions can be no more than 128MB in size, so if you need more space, you have to create multiple swap partitions. Thus, if you have a Linux system that needs two partitions for Linux (one for the system files and one for user files), plus a swap partition, you need to define two Linux partitions and one 32MB swap partition.