The nomenclature used for referencing software releases and updates can be quite confusing. Let's consider an example to illustrate what the various terms mean.
As a new version of a product is being developed, it may be made available to select customers and community members for early testing. This is sometimes called alpha builds of the product.
As development progresses and the product becomes more and more polished, it's provided to a wider audience. This used to be called beta releases; for example beta 1, beta 2, etc. However a few years ago Microsoft changed the terminology for SQL Server pre-releases. They are now referred to as CTPs (Community Technology Previews). You can download the November CTP, for example.
As the product enters it's final stages before release, the feature set is complete and the product is undergoing final testing, it's called an RC (Release Candidate).
After a product has undergone significant testing and it's determined that no more changes will be made to the product before release, it's sometimes said that the product has gone golden. It's also called a GA (General Availability) release.
Once the bits been turned over to a company to mass produce the media (CDs, DVDs, etc), it's RTM'd (Released To Manufacturing).
Usually sometime around the RTM, the product version is "launched". The timing of the launch may or may not have any correlation with the time the product is actually available for purchase. The launch has more to do with marketing and product feature education than availability.
Finally the product is released! It's available for purchase from the normal distribution channels.
Over time, Hot Fixes are created by the dev team to address specific product issues affecting certain customers. Sometimes the issue is so wide spread, a GDR (General Distribution Release) is issued so that all customers will receive the updates.
Since hot fixes and GDRs are designed to quickly address specific problems encountered by specific customers, they can be issued rather often. The rapidity of the hot fixes and GDR's makes it impractical for many IT shops to keep up with the pace of the releases. So, a CU (Cumulative Update) is created that contains all of the applicable hot fixes. This makes it easier for customers who haven't been directly affected by the issues that sparked the hot fixes to remain current.
Once a large enough collection of changes have been gathered, an SP (Service Pack) will be issued. Historically, SPs have also been the release vehicle used to deliver new features that were not ready at the time of GA. For example, Database Mirroring was made available in SP1. SP2 brought us the custom reports as in the Performance Dashboard. Microsoft has since indicated that SPs will not be used as a release vehicle for new features.
And then the whole cycle starts overs. Feel like you're on a treadmill yet?
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