Partition Recovery: Difference Between factory.wim & base.wim?

Hi,

I've a Dell OptiPlex 3020 desktop and I noticed that on the recovery partition, there are 2 identical WIM files split into 2, but with different name and path:

• factory.wim (3.30 GB) and factory2.wim (3.46 GB) on \dell\image
• base.wim (3.30 GB) and base2.wim (3.46 GB) on \preload

I noticed that it's the base.wim files that are used when you do a factory recovery from the recovery partition on the HDD.

So my question is: what's the purpose of the factory.wim files, those being an exact copy of the base.wim files in terms of size?

Additionally, why have the WIM files been split into 2 files?