The 4 gig patch is only for version 1.5 of SH4.
The issue is that SH4 pretty much stops using anything over 2 gigs. Now first off your video card should be set up so that it is handling all the functions and using it's own onboard ram and not your system ram. Many people think you put a card in and it will simply use it but many cards are set by default to use the CPU and main board ram to handle GPUs so you have graphics capabilities until the card is installed and turned on through it's own software.
Here is basically what the 4 gig patch is doing but this will discuss it better and allow you to do it yourself without using the 4 gig patch.
http://www.subsowespac.org/the-patro...ry-boost.shtml