Windows Vista that I installed on a Pentium 4 laptop computer, that I upgraded the ram to have all the Windows Vista requirements; is running good since I replaced the original old (HD) hard drive, with a new one. I prefer using new Norton Antivirus software for Windows Vista, because it uses less (RAM) memory; so it can run around 83 % faster than most other Antivirus programs. My lap top is 1-3 years older than Windows Vista.