As a matter of course, with ever ISO I open it up in UMDGen 4.00 and 'Optimize' it. I then save it as a CSO with compression level 9.
I'd say about 95% of all ISO's then work perfectly on the PSP. However there are a number that I've come across which either crash the PSP or just don't load.
Tony Hawks Project 8
WWE Smackdown vs Raw 2007
Mega Man Maverick Hunter X
Mortal Kombat Unchained
Test Drive Unlimited
Would the 'Optimize' process be stripping out files needed for the CSO to run? Or is it just that the above games just don't work regardless?
In laymans terms, what does the 'Optimize' feature actually do?
As I say, I run this as a matter of course, as it can reduce an ISO from anything from 20mb to 200mb+ sometimes. But I'm just curious as to whether this process is the cause of some CSO's not working on the PSP?
As far as I remember from using UMDGEN, "Optimise" doesn't affect the running of CSO's and I believe it only just gets rid of the extra space. Someone should be able to give you the definition of Optimise, but not myself, as I've hardly used it.
If you are compressing your images then there is no need to use the 'optimise' feature. When optimising, UMDGen removes all excess padding and dummy files (this is all it does). There is no need to perform this step if compressing as the data 'optimise' would remove will be compressed to almost nothing anyway.
On a side note, I cannot get Tony Hawk's Project 8 to run as a CSO, so you may want to try to just use it as a simple uncompressed ISO. I am currently trying to uncompress my CSO of Tony Hawks Project 8...but linux is not cooperating very well >_<