QUOTE(donpapachino @ Jul 24 2010, 04:36 AM)
if im not mistaken, for ssd you need to allocate ~20% free space, so that the drive wont suffer from performance degradation.
so if 80gb less 20% free space, actual can use until 64gb only, before taking a performance hit.

QUOTE(saturn85 @ Jul 24 2010, 05:20 PM)
hey, is that means if i have an 80GB SSD, to avoid performance hit,
then i can only format 64GB to use, then the other 16GB leave it unformat?

That used to be the case on 1st gen SSDs (especially those based on Intel) which doesn't support the TRIM command.
So the issue becomes that the drive will get a performance hit over time, wherter or not if you allocate ~20% of space.
These days, SSDs which has the TRIM command doesn't suffer from this issue.
Indilinx, Marvell and Sandforce based SSDs all have the TRIM command supporterd under Windows 7.
However the biggest issue now for SSD (aside from its price obviously), is that Sandforce based SSDs (which provides some of the fastest SSD around the market) suffers from file compression.
Earlier this year, SSDs that are built with the Sandforce controller would come on the pack saying it has 128GB of storage space but really the actual formatted space that you get is only 93GB or so.
The issue is getting resolved now, but Sandforce based SSDs despite being one of the fastest and probably the best value for money (other than cheapo Indilinx Barefoot Eco controllers) still does suffer from the file compression issue.