Gamespot has displayed the following chart which shows generally that the PSP slim loads up a range of games quite a bit quicker than the original Sony PSP.

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Finally, we got to the memory-load testing. You'll find the new "UMD Cache" option in the System Settings Menu. According to the scrolling description, enabling the UMD Cache will "reduce the frequency at which the system reads from the UMD." We enabled the UMD-caching feature and tested a few games to see if it had any affect on load times. UMD caching requires an initial memory load, so we also tested how fast the games could load up levels after we first started and exited a game to preload the data into system memory. We had time to test out only three games, but early results indicate that the additional system memory and UMD caching really do help speed up initial game launches, as well as subsequent level reloads.