OAB Version 4 is a new addition to the Offline Address Book infrastructure. It was designed to help remove most Outlook OAB download related problems
Once Exchange 2003 Service Pack 2...
Updated Jul 01, 2019
Version 2.0
Blog Post
I know the Outlook team spent a lot of time tuning the OAB V4 update code on limited memory machines. I've been running V4 on my own laptop with 384meg of ram for some time now and the performance and usability is much much better than it was for V2 or V3. I rarely even notice when the OAB is being updated.
Part of the problem with V2 and V3 was that the underlying file formats required large numbers of random disk updates to merge in the changes which tanked the machine for long periods of time. The V4 format, reads the file in sequentially, streams out the new file sequentially and uses a fixed amount of memory that grows linearly with the number of change files being applied. After that is finished, the client then reindexes the file using a new tuned algorithm.
Part of the problem with V2 and V3 was that the underlying file formats required large numbers of random disk updates to merge in the changes which tanked the machine for long periods of time. The V4 format, reads the file in sequentially, streams out the new file sequentially and uses a fixed amount of memory that grows linearly with the number of change files being applied. After that is finished, the client then reindexes the file using a new tuned algorithm.