I compressed some .iso's to .cso using UMDGen which works fine. I then 7-zipped the untouched .iso's in .7z files. Weird thing is, is that when I uncompress them and check their hash values (CRC232/MD5), they're different from the original values.... Take 'Castlevania_Dracula_X_Chronicles_USA_INTERNAL_READNFO_PSP-pSyPSP' for example. Untouched CRC32 value of the .iso (psy-cvdp.iso) is 26316F37. I then compress the .iso with 7-Zip 4.57 and these settings: When I extract the .iso from the freshly created .7z the CRC32 value of the .iso is DBD39D16. What's gone wrong? I thought file compression with archives like .rar, .zip and .7z was supposed to be lossless? Is there some kind of value or small bit changed that has lead to the hash value change? Afaik that shouldn't be possible. Maybe my HDD (Samsung 500GB SpinPoint HD501LJ), CPU (Athlon 64 X2 4200+) or RAM (2GB OCZ DC Platinum) is broken? Though WinRAR with best settings creates .rar's that leave the .iso's fine (but .rar's are way bigger, and I deleted the original .iso's XD) Could someone verify this with any regular PSP .iso? You can check hash values with QuickSFV, HashTab or from within WinRAR (files inside an archive). Maybe 7-Zip is just broken, but it bothers me because I deleted the original .iso's.