User Guide

Virtual PC 4.0 for Windows User Guide

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IMPORTANT

In general, the two linked disk image types should only

be used by advanced users logged into the host PC as an

administrator. In this mode, Virtual PC is accessing data from the

host PC hard drive at a very low level. If the virtual machine OS

crashes or contains bugs, the host volume might be corrupted.

Disk image linked to host volume

—You can link a disk image to a

volume on the host PC. In this case, the disk image is a small place-

holder that simply refers to a partition on the host system. If the asso-

ciated volume is mounted by the host PC OS, Virtual PC can only

read from it. If the volume is not mounted by the host PC OS, you

can choose to allow writing to the volume.

With this type of disk image, Virtual PC creates a virtual boot parti-

tion and partition map containing one entry. The virtual boot parti-

tion is saved to the disk image ﬁle, so changes to the sector are

persistent. All other read/write requests are forwarded directly to the

host volume.

Disk image linked to a host physical drive

—This type of disk image

is similar to an image linked to a host PC volume except that it repre-

sents an entire host PC hard drive, potentially with multiple volumes.

With this type of disk image, Virtual PC uses the real boot partition

and partition map from the host PC drive. All read/write requests are

forwarded directly to the host drive.

Disk image ﬁle splitting

Because of limitations inherent in some host operating system and

volume formats, it is sometimes necessary to split dynamically

expanding disk image ﬁles. In particular, FAT16 and FAT32 volume

formats only support ﬁles up to 2 GB and 4 GB in size, respectively.

For example, if you use an 8-GB dynamically expanding drive image

formatted for FAT32, Virtual PC splits the drive image into four 2-GB

ﬁles. Dynamically expanding images and differencing images are split

at the point where they cross the ﬁle size limit imposed by the under-

lying volume format. If the disk image is located on a volume that

doesn’t impose these limitations (such as NTFS), the disk image is left

intact.

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