Automatic windows online update ran really slow -- any idea why?

hey

i've been having this little balloon come up regualrly lately telling me updates are available for windows, and have ignored it. today, while online, i clicked on the balloon to let it go ahead & my internet connection ran REALLY slow
for a while -- web pages loaded extremely slow, and the win update was progressing very slowly also. yet, late in the download, after i'd left the computer alone for 15-20 min and the update counter was at 82%, pages were loading normally. the update stuck at that percentage for a while, and i was worrying that maybe it had a problem, and then that little icon in the system tray with the globe & the windows logo was gone, like it had finished.

any idea why this was so slow & erratic?

just trying to understand my pc better.

thanks!