Creating a Virtual Disk with VDISK.SYS Or RAMDRIVE.SYS

The DOS utilities VDISK.SYS and RAMDRIVE.SYS let you create a virtual hard drive using your computer's memory (RAM). This can be useful for various purposes, especially if your computer doesn't have a hard drive or the HD is very small (or has failed).

By adding a line to your computer's config.sys file (explained later), you can activate this feature and decide how large the virtual hard drive should be. The size should not exceed the amount of memory your computer has, or the amount needed to run programs. For example, if you have 640K of memory and want to run a program which requires 256K of memory, the virtual hard disk can be no more than 384K (640-256=384) in size. The size should always be specified in kilobytes (K/KB).

One purpose of creating a virtual hard drive in memory is to make a program available at all times without using a real HD. This way, if you want to format ten disks (for example), you don't have to put the disk with the "format" command on it back in the disk drive between each format. Using a virtual hard drive also reduces the amount of HD and/or disk use, thus decreasing noise and making these devices last longer. You can use a virtual disk/HD to run a program which normally reads from the disk very frequently when it is run from a regular disk drive. For example, the game Space Quest I reads from the disk every time the player moves to another screen. When the first disk (or all files except vol.2, unless you have extended memory and can fit the entire game) is copied to a 335KB virtual drive, much of the game can be played without needing to read from a disk - which also speeds it up, because access to memory is usually faster than floppy (esp.) or HD access. The Sierra program "Sierra Christmas Card" can be entirely copied to a 250KB virtual drive, which prevents the long pause and disk reading between songs and animated scenes.

To activate a virtual drive, first determine whether your version of DOS includes VDISK.SYS or RAMDRIVE.SYS. Then add the appropriate line to your config.sys file (located on the start-up drive or disk):

DEVICE=VDISK.SYS 256
DEVICE=RAMDRIVE.SYS 256