Unlike the average seek time, which is primarily a function of the drive's head mechanics, the average access time highly depends on the spindle speed of a hard drive. When the read/write heads are positioned, drives may have to wait for up to a full platter rotation before data can be read or written. Perhaps surprisingly, then, the benchmark results show that the 1.8" models have access times that are not much slower than comparable 2.5" drive models that also run at 4,200 RPM.