ZEROFILL writes zeros on your empty disk space for the selected drive allowing virtual machine and disk compression software to compact the allocated space in the volume and reduce disk usage.
Usage: ZEROFILL [drive:]
Examples: ZEROFILL C: Will fill with zeros all available space in drive C.
ZEROFILL has been specially optimized to run on pure DOS environments, no matter if they are on the top of physical machines, or virtual machines. It is written using Open Watcom C++ 2.0 beta, with plain C language using DOS tiny memory model to keep it compact.
Even if FAT32 partitions are not supported, its 64-bit arithmetic should make it support volumes of up to 256 GB in size, depending if DOS can adequately inform about it on service 36h. If not, it will only be able to fill reported size at most.