Write bandwidth is the least important kind of bandwidth
because usually programs write continuously only when they prepare areas
of memory. The percentage displayed is the gain in write bandwidth when
data are written using 64 bit floating point writes instead of the standard
32 bit integer writes. Intel does state in the new version of its
optimization manual (4.5.2.1), that by writing using 64 bit MMX instructions
an increase of 30% was measured. But a program relying on MMX writes
is not compatible with all the non MMX Pentiums, M1 and K5 processors out
there. That's why we use 64 bit floating point writes and achieve up to
100% higher performance.