HD Tach is a physical performance hard drive test that uses a special kernel mode VXD to get maximum accuracy by bypassing the file system.
We look at average (not peak!) write performance in this test. In addition to sequential read performance, HD Tach tests the drive's random access time. Random access is the true measure of seek speed. Many drives advertise sub 10 millisecond seek speeds, but seek speeds are misleading.
Also again, without a physical head that moves around, the SSDs are just so fast as they have no mechanical moving parts. Here obviously, the smaller the number is, the better. In this case, 0.1 ms.
SanDisk Extreme II 120 - 240 and 480 GB SSD review We review the SanDisk Extreme II series SSD which we benchmark and test. These SSDs are made 90% by SanDisk themselves including the PCB design and the NAND flash memory. The end result is a blazing fast SSD series that even surprised us.