Windows 2000 was originally supposed to be Windows NT 6.0 but was renamed Windows2000 but is still based on NT 4.0, which is known for being more stable. So one of the biggest pluses about Win 2000 is the installation is extremely easy. You can make a couple of choices and walk away while it installs itself.
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A great new Explorer feature is the thumbnails view: it shows you a preview of each file, very convenient for folders with images. It is also easier to open files with multiple applications and the mouse pointer shadow, everybody loves it but it eats up loads of processing power. Windows 2000 in general is bloated and takes up gobs of space on the hard drive, that is one of the disadvantage. .
The web server is very handy if you do web development: even Professional includes IIS 5.0 (with some limitations: only one website, limited to 10 concurrent connections). You can configure every aspect of the web server, compared to the Win98 Personal Web Server which has a very limited administrative interface. Windows 2000 is not for the avid gamer but more so for internet gooroos. The reasoning for this is the sub system is different from Win98 because Win 2000 is solely based on 32bit technology instead of the previous Win98 16 bit.
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Although the OS is more stable, it has a lot of hardware conflictions and can create havoc while trying to configure all of your hardware. OS users have to move USB printers and other devises to parallel ports. Also there is no third party driver support at this time.
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Windows has a new driver verification system that will help prevent buggy drivers and offers kernel-move write protection. It lets the system mark memory as pages used preventing processes from overwriting important applications.
The OS lacks DOS but can emulate DOS which can lead to some compatibility problems. Over all my personal preference is stability, which is more important than anything else.