Windows 8 does reserve 20% of your bandwidth for update only. Unlike the problem posted above by somebody who obviously doesn't have windows 8 this bandwidth reserve problem is real.
Its not a specific problem for windows 8 only other OS do this also. Luckily its a easy fix in the registry. Ill recommend a guide but your best bet is to Google it yourself and do your own research.
Source: random Windows 8 blog
Windows 8 by default reserve approximate 20% of your bandwidth for its own use if you are using a broadband connection, all is due to the Windows 8 frequent updates and validation processes, if we will disable this in Windows 8 we can use that rest of 20% internet speed which had been settled for updates. - See more at: http://filescrop.blogspot.com/2012/1....8Ydq7F4D.dpuf