OS/2 Warp FAQ List (20 Feb 95) Section 0403

(4.3) Hard Disk Partitioning

What is the best way to partition my hard disk for OS/2 Warp?

There is no single best way to partition your hard disk for OS/2 Warp. For some advice on the subject you should consult the printed documentation accompanying OS/2 Warp. Opinions vary, even among experts.

What is partitioning?

Your PC's hard disk is organized into sections called partitions, much like an apartment building is split into separate units. Each section or unit can be used for a different purpose, with different furniture (files) contained inside. Like an apartment building, the partition walls can be torn down, moved, and rebuilt, but usually at great expense and with a lot of disruption. The furniture (files) must be moved out of the unit (partition) and saved before remodeling (repartitioning). When you run out of space inside a partition, you can either split your furniture (files) among two or more units, or you can remodel.

With DOS (and with OS/2 Warp) partitioning may not even be a concern because it may have been done already, automatically. Quite often your PC arrives with one hard disk containing just one partition -- the simplest configuration. When you install OS/2 Warp, by default it will be copied alongside DOS (if it exists) to this one partition (Drive C), and you will be able to switch between plain DOS and OS/2 Warp using DualBoot. (An icon is placed in your OS/2 Warp Command Prompts folder which lets you switch to plain DOS, and the BOOT /OS2 command lets you switch back to OS/2 Warp. Note that the BOOT program is located in the \OS2 directory, so you may have to use the command C:\OS2\BOOT /OS2 so that DOS can find the program.)

However, there are reasons why you may wish to set up separate partitions and/or repartition your hard disk(s). In OS/2 Warp, the FDISK utility (or the Advanced installation program) allows you to repartition. First some definitions:

Primary Partition
Primary partitions have the following restrictions: (1) DOS can only boot (start) from the first primary partition with a logical drive (Drive C) on the first hard disk in a PC; (2) A maximum of four primary partitions are allowed on each hard disk; (3) Every PC must have at least one primary partition somewhere; (4) A primary partition can contain only zero or one logical drive.
Extended Partition
The other partition type for DOS and OS/2 Warp, which has none of the restrictions noted above.
Logical Drives
Both DOS and OS/2 Warp use drive letters (Drive C, Drive D, etc.) to refer to logical drives. A primary partition contains either none or one logical drive, while extended partitions can contain many logical drives.
Boot Manager
A special primary partition, one megabyte in size, which comes with OS/2 Warp and which can be installed by OS/2 Warp. If installed and active, Boot Manager presents a menu when you start up your PC, listing all the available operating systems you have placed on the menu. You can then select any one (such as DOS or OS/2 Warp) from the menu. Boot Manager also features an optional timeout. Boot Manager is required if you wish to start OS/2 Warp from any drive other than the first primary partition (logical Drive C), and it allows OS/2 Warp to be started from a logical drive in an extended partition.
Installable Drive
During partitioning, one logical drive must be set as installable (to indicate to the OS/2 Warp installation program where OS/2 Warp should be placed).
Startable Partition
A startable partition is one that should be looked at by your PC as it starts. If an operating system (or Boot Manager) is found, it will be started and run. At least one partition must be startable.

These definitions hint at some complexity should you decide you wish to partition your hard disk(s) in some way other than single, large primary partition(s). Remember that repartitioning involves backing up all your files, partitioning your hard disk as desired, reformatting each logical drive, and restoring files. (See below for an exception to this procedure.) Consequently, because of the work involved, you may opt to avoid repartitioning anyway. (It also means that you should think carefully about how to organize your hard disk(s) so that you avoid work later on.)

Some Advice

To simplify these decisions, you should keep in mind that, in general, partitions are meant to be used to separate that which must be separated of necessity. The partitioning system was invented to allow your PC to store multiple operating systems which had different types of file systems (in other words, different ways of storing files on your hard disk). DOS uses the so-called FAT (File Allocation Table) file system, for example. Unix might use a Berkeley file system, a completely different way of storing the information required to manage directories of files. Because these file systems might be incompatible, separate areas of the hard disk (partitions) must be set aside, with one operating system never touching the other's partition(s).

OS/2 Warp (in its basic package) supports two file systems: the DOS FAT scheme and HPFS. So, as you might expect, if you want both DOS and OS/2 Warp, and you wish to use HPFS on the same (physical) hard disk, you need two partitions (one for DOS and its FAT file system, one for HPFS), even though OS/2 Warp itself could be located on the FAT logical drive. You want to choose partition sizes so that each logical drive can handle expected growth in the number and sizes of new files that are added to each.

That advice suggests (correctly) that you should not impose separate partitions for other reasons, generally speaking. For example, never create a separate logical drive for your OS/2 Warp swap file or print spool files. Also, it rarely makes sense to create a separate drive to divide application or program files from data files (for backup purposes, for example). With both DOS and OS/2 Warp's file systems, subdirectories should be used for that purpose.


There are reasons why you might be forced to create separate partitions despite tendencies not to. For example, the DOS FAT file system grows less and less efficient (from both a performance and storage standpoint) as the size of a logical drive grows. Moreover, the FAT file system can only cope with a maximum partition size of two gigabytes. Hard disks larger than 2 GB using the DOS FAT file system must be divided. Also, on many PCs, because of BIOS restrictions, your startable (primary) partition must be physically located entirely below the 1024th cylinder on your hard disk (or, roughly speaking, it must be no larger than about 511 MB). When the original IBM PC was designed and first sold in 1981, hard disks were small, (usually 10 MB or less in size), expensive (in the thousands of dollars), slow, and relatively uncommon, so the BIOS built into the system was never designed to boot from such "enormous" hard disks. While your first, startable partition (the one containing DOS and/or OS/2 Warp) must often be located entirely below the 1024th cylinder, another partition can be created which spans this cylinder and occupies the remainder of the hard disk (HPFS recommended).

"Ideal" Arrangements

What does all this boil down to? In a perfect world, starting from scratch, there are probably two common, "ideal" configurations. If you wish to use both DOS and OS/2 Warp on the same PC, and switch between plain DOS and OS/2 Warp easily, you should partition your hard disk as follows:

  1. Boot Manager (1 MB);
  2. Primary Partition with Drive C, FAT file system, containing DOS (large enough to contain DOS itself plus all the files which you expect you will need to get access to when running plain DOS);
  3. Extended Partition with one logical Drive D, HPFS, containing OS/2 Warp (remainder of the hard disk).

If you wish to use OS/2 Warp exclusively, there's probably nothing better than:

  1. Primary Partition with Drive C, HPFS, containing OS/2 Warp (entire hard disk).

Of course, we do not live in a perfect world, and you are probably not starting from scratch, so, for sheer convenience (or other reasons), your chosen partitioning scheme will vary. If you find that the partitioning you choose does not suit you, the worst that can happen is that you will need to create a complete backup of all your files and restore those files after reorganizing your hard disk. A new software package called Partition Magic from PowerQuest can ease even this procedure, because it allows both on-the-fly conversion of FAT to HPFS (keeping files intact, where they are) and, as long as free space permits, movement of the partition lines (a bit like a sliding wall in an apartment building). Regardless, you should have a backup strategy that preserves all your important information.

How are drive letters assigned?

A common source of confusion arises with the assignment of drive letters. Both DOS and OS/2 Warp use drive letters (C, D, etc.) to refer to logical drives. Some applications (including Windows and OS/2 Warp itself) depend on these drive letters to a great degree, so that if you repartition, and the drive letter changes (so that the application believes it is located on a different drive, because a different drive letter was assigned to its drive), the application may not run correctly (or at all).

OS/2 Warp assigns drive letters in the following order (with some oversimplification here):

  1. A and B are reserved for the first and second diskette drives in the PC, regardless of whether or not they are actually installed and available.
  2. C is assigned to the first logical drive found in an active primary partition. In practice, C is assigned to the logical drive containing DOS or, if installed to a primary partition, the logical drive containing OS/2 Warp. If C is not assigned to a primary partition's logical drive, and that primary partition is physically located ahead (in front) of the logical drive which was assigned C, that primary partition will be totally skipped. In other words, if the partitions are as follows:
    1. Boot Manager
    2. Primary Partition (DOS, FAT)
    3. Primary Partition (OS/2 Warp, FAT)

    then, when OS/2 Warp is started, the primary partition containing DOS will not be assigned a drive letter, and the drive containing OS/2 Warp will be assigned C. When DOS is started from the Boot Manager menu, the drive containing OS/2 Warp will be assigned D. (This "shift" in drive letters argues for having only one primary partition when using Boot Manager, or for making the OS/2 Warp primary partition HPFS, which is skipped by DOS.)

  3. The next drive letter(s) (D, E, etc.) is(are) assigned to the remaining primary partitions' logical drive(s), in sequence, located on all the hard disks in the system.
  4. The next drive letter(s) is(are) assigned to logical drive(s), in sequence, in the extended partitions located on all the hard disks in the system.
  5. The next drive letter(s) is(are) assigned to other devices connected to the PC (such as CD-ROM drives).
  6. Drive letter(s) can then be assigned (not necessarily in sequence) to remaining drives, such as network drives.

Confused by all these partitioning rules and outcomes? Remember: keep it simple.

Related information:

(1.5)  High Performance File System
(3.2)  Shareware and Freeware Sources
(3.12) Backup Software
(5.6)  Performance Tuning

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