ED = Early Deployment
GD = General Depolyment
All released of PIX code, when they are first released, are ED releases. After meeting a certain set of circumstances such as open bugs, time in field, etc..., the releases can move to a GD status. GD generally means that they are considered to be more stable releases. The trade off between only running GD releases is that you do not get the newest features in a timely manner as you have to wait for the status to change.
Does this help?
Scott
