HD Tach — continued
Our RAID configs have an unfair advantage here by virtue of their use of multiple Serial ATA connections. Otherwise, performance in HD Tach's burst speed test appears to be gated by the practical throughput of the 300MB/s SATA interface. 262MB/s is as fast as we've seen from a single device, with most managing over 200MB/s.
There's a second tier of sorts starting at around 137MB/s. Here we find drives designed for the older 150MB/s Serial ATA specification. A bunch of our 2.5" drives are also IDE models with interfaces capped at 100MB/s.
Perhaps better than any other set of results in this retrospective, our collection of HD Tach random access times clearly illustrates the seek time advantage that solid-state drives have over their mechanical counterparts. Raptors aside, even the quickest mechanical drives are a full two orders of magnitude slower than the SSDs here.
SSDs don't have to deal with the mechanical or rotational latency inherent to traditional hard drive designs. They don't have to move a physical drive head, and they don't have to wait for data points to come spinning 'round on a platter. Increasing spindle speeds is one way to lessen the impact of latency, and as the 10k-RPM Raptors illustrate, doing so can greatly improve random access times.
With only the Raptors exceeding 7,200 RPM, we haven't seen random access times fall all that much for standard desktop drives. In fact, the old Barracuda 7200.7 and Deskstar 7K500 still have among the quickest access times we've measured for mechanical drives. The higher precision required to quickly seek out data on drive platters with ever-increasing areal densities is a challenge for newer models. Some have risen to it, while others have stumbled. The new Barracuda 7200.12's 17-millisecond access time is particularly disappointing
The access times of mobile hard drives are predictably higher than those of their desktop counterparts. The slower spindle speeds of the 5,400 and 4,200-RPM drives don't help, but even the 7,200-RPM models lag a few milliseconds behind their 3.5" brethren.