The system will notify you that it cannot perform this conversion because the system is using this disk. You are prompted and asked if you want the conversion to take place at the next boot up. Reboot the machine, for the changes to take place. There are a number of service packs out there, both for different versions of Windows NT and Windows 2000. Service packs are the means by which Windows NT product updates, patches, vulnerabilities are distributed.
Service packs are cumulative.
This means that SP6 contains all of SP1 through 5 as well as the fixes introduced in older versions to Services Packs. Service packs often update a great amount of code by replacing major DLLs. Hot fixes are intermediate fixes released between service packs and are not considered fully regression tested, and as such not recommended by Microsoft to be applied unless one really need the feature they provide. Lately, a bunch of security problems have been solved by means of releasing hot fixes. Service packs and hotfixes are the means by which Windows NT product updates, patches, vulnerabilities are distributed.