I have been using linux for about a year, but I have never upgraded from one version of a distro to a newer version of the same distro. Instead, I have tried numerous distros such as RedHat, Mandrake, Ubuntu, Vector, and some others. A few months ago, I started using Fedora, and I like it so much that I have decided to stick with it.

Right now, I have Fedora Core 3 installed. If I apply all of the updates as they come across the Red Hat Network, will I have a different system than if I installed Fedora Core 4? Also, I guess that my question applies to all distros, is there a difference between updating all of the packages in an older version distribution versus installing a newer version of a distibution?

Basically, "updates" maintain the same core group of software where "upgrades" can differ quiet a bit. For instance, it's unlikely that Slackware 10 will ever officially use the 2.6.x series kernel, since it was built around the 2.4.x series. However, it is likely that Slackware 10 will continue to be maintained for years to come. That is to say that any security updates, bugs, and etc will be addressed as they arise.

In contrast, Slackware 11 will most likely feature a 2.6.x series kernel by default, along with a host of other newer software versions than is in 10.

So in general, no, a system that has been maintained with all the lastest updates will not be the same as the very lastest release of that distro. Of course that assumes that you stick to updates to your specific version and aren't venturing into upgrading to the bleeding edge so to speak as a distro is developed. For instance, with Slackware you can keep it upgraded to what's referred to as Slackware-current. Slackware-current is the bleeding edge and when Slackware 11 is released it will be an exact replica of it. You can do that with alot of distros, not just Slackware, but it's generally not a good idea if a distro is undergoing drastic changes such as is the case with Slackware as it transitions from 10.1 to 11.

You can also "upgrade" a distro to the next version all at once in most cases. Like say when Slackware 11 is released, you should be able to upgrade Slackware 10 to 11. You'd then have 11 not 10. That make sense?

In the Debian context and probably RH based systems using apt then the instruction to update means that the packages available via the mirror are updated. An upgrade occurs when you actually upgrade these packages from the mirror. Packages may be modified due to security flaws for example and then when you do an update it notifies you that an updated package is available. When you upgrade the original package is replaced with the new one on the system.

In context to Debian, an update is used to resynchronize the package index files from their sources. The indexes of available packages are fetched from the location(s) specified in /etc/apt/sources.list. An update should always be performed before an upgrade. And on the other hand upgrade is used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list. An update must be performed first so that apt-get utility knows that new versions of packages are available.

-Prasanta