Shrinking VirtualBox VMs

This article is note to self, as I just gather information from other sites:

• https://www.howtogeek.com/312883/how-to-shrink-a-virtualbox-virtual-machine-and-free-up-disk-space/
• http://www.surfacetablethelp.com/2016/06/fix-ssd-optimize-drives-not-available-in-windows-10.html
• https://www.techrepublic.com/blog/tr-dojo/delete-hiberfilsys-by-disabling-windows-hibernate-function/
• https://windirstat.net/download.html