NullWriter

NullWriter is a lightweight and portable piece of software designed to reduce the size of virtual machine files, such as the ones made by VMWare or Virtual PC. It must be run inside the virtual machine and it will create large-sized files to occupy free space on the virtual disk. Once they are deleted and the VM is turned off, the compression ratio will theoretically increase.

Portability perks

There is no installation involved, so you can save the executable file to any part of the virtual disk and just click it to run. It is also possible to save it to a pen drive or other removable storage unit, to be able to directly run it in the virtual machine. More importantly, unlike most installers, NullWriter does not modify Windows registry entries or create additional files on the disk without your permission.

Simple-to-use interface and options

The GUI is made from a single, small window that does not contain any visually attractive elements, yet it is easy to navigate. It provides direct access to all available options.
So, all you have to do is select the local drive, file size (in megabytes) and file name. Optionally, NullWriter can be asked to overwrite the file if it already exists, as well as to delete it after completion automatically. There are no other noteworthy settings provided by this software application.

Evaluation and conclusion

There were no kind of stability issues throughout our tests, since NullWriter did not hang, crash or pop up error messages. It has a good response time and quickly creates the fake file on the disk, regardless of its size. CPU and RAM consumption was low during this time, as we expected.
To sum it up, NullWriter offers a fast and effective method to creating large files with a fake size in order to delete them afterward in the attempt to increase the compression ratio when reducing virtual machine files in dimension. However, it has not been updated for a long time.