From the release notes on the patch 3 for VSE 8.7:
" In some situations, the product switches over to using the normal copy of the DAT files, instead of the runtime DATs: "
What is the difference between the two?
The Runtime DAT is Optimized for high local performance. It is a rebuild (as some might say) of the normal DAT files, so that the memory and CPU resources needed to operate are balanced for best performance.
The Normal copy of DAT files are much simpler in format with optimization designed for downloads of daily incremental files (signatures). So, downloading the normal DAT updates has a priority of using as little bandwidth as needed, but is not well optimized for local performance.
In it's simplest form:
Normal DAT = Faster download
Runtime DAT = Faster system
Hope this helps.
Thanks, great answer.
Your Welcome, and Good Luck.