Using multiple hard disk images

Although LDOS hard disk images are limited to 64MB in size, M3SE is capable of accessing alternate images on an IDE/CF disk. The 64MB restriction results from LDOS' inability to address more than 1024 cylinders or 8 heads on a disk. IDE, however, permits as many as 65536 cylinders and 16 heads.

To see how many images your CF card can hold, run the IDEBOOT utility without any arguments. This will display the active image number, a number of complete images and a number of partial images. Complete images consist of 1024 cylinders, regardless of how many are actually used by your logical disks. Partial images can use up to the number of cylinders shown. The minimum 2GB CF cards shipped with M3SE can usually hold six complete images and two partial images.

M3SE comes with only the default image, number 0, populated. Before you can boot an alternate image you must first populate it.

Use the IDEBACK utility to copy the entire current image to another image:

	IDEBACK (DEVICE=d,IMAGE=i)

The device number is 1 for the Primary IDE device (CF card) and 2 for the Secondary. The image number ranges from 0 to the maximum allowed on the specific device, as determined by its number of cylinders and heads. For example, this command:

	IDEBACK (DEVICE=1,IMAGE=1)

copies the current image on the primary device to the second image on the primary device, after which you can IDEBOOT 1 if the current image is bootable. And the command:

	IDEBACK (DEVICE=2,IMAGE=0)
or just
	IDEBACK

copies the current image to the first position on the secondary IDE device, making that CF card bootable if it is moved into the primary IDE slot. You cannot directly boot images on the secondary IDE device.

The two images must be the same size (that is, both complete or both identical-sized partial images). Be aware that doing this will overwrite the entire contents of the destination image.

The time required to perform an image copy varies with how much disk space is used. Allocation units (grans) that are not part of any file are not copied.

After populating an alternate image on a CF card (that is, IDEBACK to image number > 0) it is strongly recommended that you rename (change the volume label) of drive :0 of the new image. This is because alternate images are initially exact duplicates of image 0, and it can be difficult to tell which image is currently active. For example:

	IDEBACK (D=1,I=1)
  	IDEBOOT 1
  	ATTRIB :0 (NAME="IMAGE1")

Now when you boot the alternate image, the new volume label "IMAGE1" will be displayed on the LDOS boot screen, with the FREE command, and in directory listings of drive :0.


Back to the main page