Service Packs are Comprehensive Service packs have a significantly larger scope than patches. Every service pack addresses not only security bugs, but also bugs affecting stability, performance, proper operation of product features, or other areas. In contrast, a patch is tightly focused on one and only one issue. Service packs resolve minor as well as major bugs. On the other hand, we know that customers have things they'd rather be doing than installing patches, so we only develop patches for issues that warrant the disruption they cause.
Service packs are cumulative.
Moreover, whenever we release a patch, we always include it in the next available service pack. The net result of all of the above is that service packs are the best way to keep your system in top condition. Patches certainly have their place, but even if you were to install every patch Microsoft ever released, it wouldn't eliminate as many bugs as simply installing the most recent service pack. Service Packs are Better Tested Because they're planned releases, service packs are quality-driven. That is, we won't release a service pack until it meets the same quality standards as the product itself.