Reliability and Stability
What about reliability? Planned outages for updates are bad enough, but unplanned downtime due to crashes and other problems can seriously damage your web site’s credibility as well as profitability.
One of the reasons that many give when listing UNIX as a more stable hosting environment is that it’s been in use a lot longer and has had more time to mature. UNIX has been around since the 1960s, whereas Windows is a relative newcomer that didn’t enter the market officially until the end of 1985. Even with that, Windows didn’t get much notice until the 1990s. In addition, UNIX was developed with the idea of a shared environment in mind. Windows, on the other hand, started out as a more "personal" operating system.
Although Windows has made some improvements in this area over the years, Windows servers still need rebooting much more often than UNIX ones. It’s not uncommon for a Windows server to need rebooting once a week or more, depending on the configuration and traffic. On the reverse side, UNIX servers can go for months without the need for a reboot.
All of this depends, of course, on no other problems arising. Scheduled reboots can be planned for in advance. It’s the ones that are a result of crashes and system failures that cause the most trouble. These situations can result in serious downtime. Although most claim this is more common in Windows, it’s not unheard of with UNIX systems.
One very important thing to keep in mind here is that when people talk about how stable UNIX and Windows are, they’re really referring to the operating system itself. Any application running on either of these platforms needs to be evaluated separately both on its own merits and on how compatible it is with other software in use on the system.