I was copying/moving many large files/directories (~500 MB - 2 GB) between hard drives (physically inside my system, not across a network). System is Windows 7, SP1, 64 bit, 16 GB of ram.
Some actions proceeded smoothly, albeit slowly (my perception) but once the system just seemed to "go to sleep" (single instance of a 11.5 GB transfer) - nothing happened for several minutes and then Windows apparently locked up. Only way out was a cold reboot. Nothing lost.
Are there tricks to doing this more quickly? Does Windows not like big transfers?