Extracted from 'Distributed System Guide - Chapter 22 Group Policy'
http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/distsys/part4/dsgch22.asp
Synchronous and Asynchronous Processing
Asynchronous refers to processes that do not depend on each other's outcome,
and can therefore occur on different threads simultaneously. The opposite is
synchronous. Synchronous processes wait for one to complete before the next
begins. For those Group Policy settings for which both types of processes
are available as options, you choose between the faster asynchronous or the
safer, more predictable synchronous processing.
By default, the processing of Group Policy is synchronous. Computer policy
is completed before the CTRL+ALT+DEL dialog box is presented, and user
policy is completed before the shell is active and available for the user to
interact with it.
Note You can change this default behavior by using a policy setting for each
so that processing is asynchronous. This is not recommended unless there are
compelling performance reasons. To provide the most reliable operation,
leave the processing as synchronous.
Group Policy for computers is applied at computer startup. For users, Group
Policy is applied when they log on. "
The policies are under:
Computer Configuration\Administrative Templates\System\Group Policy
