I have a server (actually it's my development VM) that's quite space-limited, and a significant proportion of the c: drive is being used by Windows to store MSP files. A bit of searching has told me these are MS-patch files for installations.
Are these safe to delete? If not all of them; how can I tell which ones are and which ones not?
Yes and No. Deleting MSP files will not cause you an problems in the short term. However it cause you problems later down the line when you try an install hotfixes or patches. MS patches are atomic, so if the install of one doesn't work, it rolls the computer back to the state it was in before the patch was applied, to do this it needs to use the information in the MSP files.
These MSP files also provide the information to repair and uninstall these patches, if you remove them you will no longer be able to do this.
