4GB held in reserve to use as cache
Recent teardowns of the 12GB Super Slim PlayStation 3 has revealed a surprising truth. The unit actually has 16GB of flash and the system is holding the 4GB in reserve for use as cache to improve performance. Apparently, it is accessible to developers to optionally use, but it is unclear if anyone other than Sony is taking advantage of it yet.
One other interesting thing is that when you insert a hard drive into the unit, it will automatically move your data from the 12GB of flash over to the new hard drive automatically, which is a nice feature; but it can be a little slow while it moves the data.
As for the actual performance, the 12GB Super Slim really is the same performance in a new package, according to reviews. Of course, it does strip down some features offered by the older models; and one may be missed, others while not.