No anti-virus software. I turned off all background processes. The drive I render to is at least 10 RPM, but the drive bryce is on is slower. It's a pain because you can't resume crashed disk renders, so I changed my resolution to 1600x1200 and rendered to screen so I could resume if it crashed. It's still not the right resolution, but the image rendered fine to screen, so it's not a problem with any of my objects or my scene file.