Sorry for posting to this old thread(probably should have created new one), but I have exactly the same question: is it possible at all to use windows 7 (x64) in pure UEFI mode? That is not only UEFI/GPT boot, but also all CSM/legacy disabled in BIOS. Has anyone succeeded in doing this? I don't understand official MS position: it seems they say that OS itself should support legacy-free UEFI operation, but some 3rd party drivers(video for instance) require CSM. For me this seems to be not true: with CSM disabled I get stuck even during safe mode(command prompt) boot just after the CLASSPNP.SYS driver is loaded, while with CSM enabled it boots OK. So the problem arises before any graphics/video driver is loaded. Maybe this happens because I have converted my installation from BIOS/MBR, but not initially installed in UEFI/GPT mode? Anyway it's interesting to know if somebody has installed in UEFI mode and has windows 7 bootable with CSM disabled completely.