How does the PXE work

Hi everybody,

i read this article http://technet.microsoft.com/en-us/library/cc738715%28v=ws.10%29.aspx

about PXE architecture and how its work but i cannot understand where does the file save (After Startrom.com has been downloaded and i pressed F12 - when the boot image is download)?

does it save on the RAM or HDD?

thanks a lot,

Gal