APT stands for "Advanced Package Tool", and is really a package dependency layer built on-top of some other packaging system. In the case of Debian, that packaging system consists of files called DEBs.
A DEB is fundimentally no different from an RPM. It is an archive of files consisting some larger program. It usually has install and uninstall scripts, a list of dependencies, and architecture information.
What makes Debian's system different is this APT-layer. APT allows the system to automatically track down dependencies for you. So, if we were to want to install package "foo", which had this tree of dependencies that would be difficult to locate and install by hand, APT would find all the dependencies for us and install them.
Using APT, a Debian-based system can very rapidly and easily be updated and new applications installed. We will look more at Debian and APT in the next two courses.
NOTE: It is important to point out that technically there is no reason an RPM-based system can't use APT on top of it. This just hasn't been done too successfully because of the severe incompatibilities between the various RPM-based distros. That being said, there are distros like PLD which are attempting to change that.
Gentoo's emerge
Emerge is a newish format that has been generating a lot of waves in the community. The idea behind emerge is to give you a simple dependency tracking system similar to APT, but to also give you a powerful source-based automated compile system somewhat similar to FreeBSD's ports (which we look at in UNIX02).
The key benefits to a Gentoo/emerge system is that you can typically have much more cutting edge applications and better hardware optimization and support.
These strengths have made Gentoo the fastest growing distribution in terms of users. Gentoo is even the distro of choice in strange places such as Novell.
Slackware
Slackware uses a very simple package management scheme. They have their system set up around simple tar-balls that can be decompressed/dearchived into the root directory and just "fall" into their proper places.
This limits the ways you can install a package, but means that the package really should just work "right out of the box".
