Can I confirm it actually reported 160GB previously on checking? As far as I am aware most of virtualisation suites just make an image file and use this is a virtual file system and so should not effect the total size of the hard drive. Most hard drives report their size in GB while operating systems don't actually report space in GB but rather GiB and these are two different measurements and as GiB are slightly larger then GB, roughly so 160GB is about 147~148GiB.
1GB = 1,000,000,000 bytes.
1GiB = 1,073,741,824 bytes.