What is RTM, GA, Retail, and OEM?

Short for release to manufacturing, the version of a software product that is given to manufacturers to bundle into future versions of their hardware products. RTM (release to manufacturing) is when the code is completed and signed off. RTM versions are typically released to manufacturers before they are released to the general public so that the manufacturers can work out any bugs the software may encounter with hardware devices. The release of an RTM version does not necessarily mean that the creators have worked out all the problems with the software; there still may be more versions of the product before it is released to the general public.

GA, or general availability, is when that RTM’s code is finally made available to the general public. Even though there are three months between RTM and GA release date, there is no difference between the RTM code and GA version code. The RTM bits are the GA bits. RTM is done with the code, and GA is done with the packaging, distribution, marketing, etc. Ready to sell.

When GA comes, you can get Windows in two flavors:

Retail, which is what you buy at a store, is a less restrictive license (you can transfer it between machines, as long as only one machine is activated at a time), and you are entitled to support from Microsoft.

OEM is a cheaper license, that you get when you get Windows bundled with a PC or if you buy a "system builder" copy. OEM is cheaper because its locked to a system (you cant transfer your license to another machine), and you are not entitled to tech support (the person who built your computer is responsible).

There are two types of OEM: regular and royalty. Regular OEM is what you get when you buy a "system builder" OEM Windows. Except for the label on the disc, regular OEM discs are the same as retail discs, they install the exact same bits as a retail disc. The difference is not in the disc, but in the key; if you activate Windows with a OEM key, the key is forever tied to your system, whereas if you use a retail key to activate, you can move that activation to another computer in the future.

The big PC makers like Dell, HP, and Sony are classified as "royalty OEMs" by Microsoft. They will often customize their disc by including logos, extra drivers, and/or hotfixes. Their discs will also include a special certificate that Windows uses to authenticate your computers BIOS.