Maybe I'm the last one on the planet to discover this horrible default setting in VirtualBox but the difference is so awesome I have to tell the world.
MAKE SURE THIS IS CHECKED! If you find it default unchecked, you'll be amazed. 
EDIT: As pointed out, you do need memory to get this advantage. In my case, I had the memory (16GB) but still bad performance. Your mileage may vary.
Very nice, thanks for the tip!
If you’ve got the RAM to spare.
My work laptop only has 8 GB which gets used up pretty quickly – having this checked in the past meant more swapping, as there isn’t enough “free memory” to cache the virtual disk as well.
It’s my understanding if the guest vm has low ram then this can increase performance. But a guest with sufficient ram you can set yourself up for double caching between the host and the guest. So what’s that magic number for the amount of ram?
My VB XP always ran much faster than VB WIN7. XP had I/O enabled, Win7 did not. Now they are both fast. Thanks.
Glad to hear it, @jaybo! I had exactly the same experience with XP vs Win7.
@anon42388993, If my guests were caching it was really really bad. 
Thanks for the read - there’s more to it than 1 setting for sure.
@lah7, I’ll add that caveat - you need memory or VMs will always be a balance when memory is low.
I get a “file not found” error for the image, could you repost?
Thanks
Joe
Without the image, kind of a tough post to understand.
Hmmmm… it used to be there. Not sure what happened to it (the link was a 404) but it was easy to replace - good catch, thanks!
@lah7, I haven’t heard other old graphics disappearing (first post here - edit has the old link). As long as it’s not a trend, I guess.
