Microsoft provides two avenues to get to Windows 7: a custom installation and an upgrade installation. Most computers will need a custom installation, however because the opportunities for in-place upgrades will be few and far between. For example, users moving to Windows 7 from Windows XP must go with a custom installation, as there is no direct upgrade option under any circumstances. Users moving from 32-bit Vista to 64-bit Windows 7 (or vice versa, if you have need to go that way) must also do a custom installation.To perform custom installations, users will need to collect and reinstall all applications as part of the process. At the very least, I would advise that users put a Windows 7- or Windows Vista-compatible driver for the computer's network adapter on a USB stick before beginning a custom install. Windows 7 will, however, keep all your data intact-- the custom installation process collects the old operating system C: drive and saves it on the upgraded system in a folder called Windows.old. In addition, Microsoft provides a link to the beta of Windows Upgrade Advisor, a program that scans the current system for incompatible programs and drivers. At the very least, users should expect their current anti-malware suites to have issues in Windows 7, so I would advise removing the application before upgrade--even if the Advisor reports the program only as a potential problem. I tested both the 32-bit and 64-bit iterations of Windows 7 Ultimate against their Vista SP2 Ultimate counterparts on a pair of machines. The first machine represents a common recent-model laptop similar to those used in businesses both large and small today: a Dell XPS M1330 with 3GB of RAM, a 2.6GHz Core2Duo T9500 processor, a 160GB hard drive and an NVidia M8400 Graphics chip. The other system I used represents a much higher-end desktop: a home-built 3.0GHz quad-core Phenom II 945 with 4GB of 1066 DDR3 RAM, a 1TB hard disk and an ATI Radeon HD 4870 X2 video card. At least from an optical media source, Windows 7 streamlined the clean install process over that provided by Windows Vista. I measured this process from first boot from the DVD to when a user could log in and interact with the client hardware system. On the Dell laptop, 32-bit Windows 7 installation took 21 minutes, compared with 32 minutes for Vista SP2; 64-bit Windows 7 took 28 minutes to install compared with 30 minutes for Vista x64. On the desktop, installation proved fast in all instances, with Windows 7 again providing the best times. Windows 7 scored 15 minutes for 32-bit Windows 7 installation and 18 minutes for 64-bit Windows 7 installation. Vista 32 bit and 64 bit installation timed at 18 and 19 minutes, respectively. These times reflect clean installs, but I found times for custom installs over old operating systems to be in the same ball park. On the other hand, an in-place upgrade to Windows 7 from Vista will take much more time--my two trials have taken between 45 minutes and an hour each. It appears that some of the disparity between Windows 7 and Vista SP2 here is due to a bit of a cheat on Windows 7's part when it comes to evaluating system performance during installation. Vista takes several minutes to run a comprehensive system performance evaluation, while Windows 7 may look only at the video subsystem performance. To wit, Windows 7 won't have a Windows Experience Index score to present to users, whereas Vista will try to accumulate the score during the installation.
Only users moving from Vista to Windows 7 within the same architecture (32 bit to 32 bit or 64 bit to 64 bit) have the option to perform an in-place upgrade, and, even then, there are limits. This is because you cannot downshift across versions: If you currently have Vista Ultimate, you cannot upgrade to Win 7 Home Premium or Professional. You can go up--say, from Vista Home Premium to Windows 7 Ultimate--though. Also of note, you cannot move from Vista Ultimate to Windows 7 Enterprise. (Check out Walt Mossberg's useful upgrade chart here.)