PSP 1000(fat) is the 1st version. -Can easily install hacked applications -Larger size than any other PSP -Long loading for certain games PSP 2000(slim) is the 2nd version. -Battery life increased -More smaller in size than PSP 1000 -System ram increased to improve loading times PSP 3000 is the 3rd version. -Same as PSP 2000 -Brighter and improved screen -Mic for skype use or other PSP GO is the 4th version. -Nearly same as PSP 3000 -UMD slot removed -Redesign model -Larger screen -16 GB of Internal Flash Memory to store games or others -bluetooth connection with PS3