Helping people with computers... one answer at a time.
Msocache is another of those "magical" directories (not a file) that somehow just appears one day. Since we're not looking for this kind of thing constantly it's easy to miss exactly when it showed up.
Here's one clue, though - MSO stands for MicroSoft Office.
Yep. Microsoft Office is trying to be helpful.
First, Microsoft does have a Knowledgebase article on this, though the title's not particularly helpful: Local Install Source (Msocache).
The bottom line is that it's simple a local copy of Microsoft Office's installation source. Put another way, it's a copy of portions of the Microsoft Office installation CD. Why? so that you don't have to insert the CD when you add a feature, perform a repair operation, or install service packs and patches.
Msocache is created, quoting the KB article:
...if the following conditions are true:
- One of the available hard drives has more than 1.5 gigabytes (GB) of free disk space available.
- The hard disk with sufficient space is not a removable drive or a network drive.
Personally that seems kind of arbitrary, but there ya go.
You can delete the folder, but, that same Knowledgebase article goes on to say, "Never delete the MSOCACHE folder by using Microsoft Windows Explorer." Why, I do not know. They suggest using the Windows Disk Cleanup Wizard.