World of Warcraft: Spell Batching in Classic WoW

What is Spell Batching?
For those unfamiliar, Spell Batching refers to how the WoW servers process incoming interactions. Instead of processing everything immediately, the server creates batches of actions (attacks, buffs, debuffs, etc) in order to process them all together. This is done to optimize the amount of time the server spends processing those effects. The side effect of this is that actions in the same batch are considered simultaneous and don't affect one another.

In the past, back when servers had less computing power than phones nowadays have, these windows could be very large, with some games having up to 200ms windows of batching, including WoW.

With better technology and servers, this system was improved over the years and, while it still exists, and effects from it can still be seen, the windows are much smaller, being 20ms wide for abilities in retail WoW. Once players buy WoW Classic gold, they will be stronger and has more abilities to beat boss in Classic WoW. This means that abilities cast within 20ms of each other are considered simultaneous in the eyes of the retail WoW servers, while this window was about 200ms during Vanilla.