Q I swapped out a FireWire drive with a new Thunderbolt drive, but the performance doesn't seem to be that much better. Isn't it supposed to be?
A Performance with drives depends on a couple of things: how fast the data can be read from or written to the drive's platters, and how data gets from the drive to the computer.
A drive's platters are platelike parts. They're covered in high-tech magnetic material that holds your data and are mounted on axles, called spindles, that rotate the platters. How fast the spindles rotate is directly related to how quickly data can be read from the drive. The faster the spindle, the quicker the data flows.
How data gets from the drive to the computer is through the drive interface. The faster the interface, the faster data can travel to the computer. The speed is referred to as the theoretical data transfer rate.
Notice that I said "theoretical data transfer rate." Much like EPA mileage standards, you don't really get that data transfer rate.
When you drive your car, things like road conditions, wind, passenger weight and how you drive may affect your gas mileage. With data transfer rates, you have something called overhead. These are data elements that help keep track of the data being transmitted.
For years, the interfaces that people have used to move data from drive to computer have been either USB or FireWire. (There are other interfaces, like Fibre Channel, for larger storage systems, but they require dedicated interface cards.) Initially, they operated at a theoretical data transfer speed of 480 Mb/s (USB) and 400 Mb/s (FireWire).
Let me pause here and mention that it's important to keep the speed units straight. Speeds can be listed in Mb/s or MB/s, and the difference is significant. Usually, a byte is 8 bits so there are 8 megabits (8 Mb) in a megabyte (1 MB). So when you see 800 Mb/s, that's 100 MB/s.
Then there was FireWire 800. The 800 was a nod to the theoretical data transfer speed of 800 Mb/s. Next, USB 3.0 arrived with its 5 Gb/s rate (5000 Mb/s). Technically, it's called USB SuperSpeed (just as USB 2.0 was called USB Hi-Speed). USB 3.0 showed up mostly on Windows machines, which left Mac users out in the cold with their FireWire. Eventually, Thunderbolt arrived for Mac users with 10 Gb/s speed.
Prior to doubling and quadrupling interface speeds, drive manufacturers only had to worry about delivering data at a speed that would keep the input/output pipe (interface) full of data. But if it can't pull data off the platters fast enough, then the transfer speed slows down. Earlier USB and FireWire drives could deliver data at the necessary rate to keep the pipe full. However, if you connect one of these drives to the newer USB 3.0 or Thunderbolt interfaces, the drive can't keep up.
As interface speeds have risen, disk drive designers have been faced with the challenge of delivering the data fast enough to keep the pipe full. Currently, you can only spin the spindle so fast and still make it accurate, reliable and cost-effective.
Drive makers have some options. First, obviously, they will try to make drives that spin faster. There's also the option of using solid-state drives (SSDs), which have no moving parts. They can provide a faster access speed. The trade-offs are cost, capacity and longevity. Also, it should be noted that not all SSDs are the same. Contrary to common misconception, SSDs aren't always faster than a hard drive.
But probably the best option to speed up drives is to use more than one. By using multiple drives and splitting the data across the spindles, data access speed increases. These multiple spindles may look like a single drive, but they can deliver much higher performance.
Multiple drives have long been the solution for large high-performance systems. A Fibre-Channel system may use as many as 16 separate drives, allowing for high-speed data transfer and redundancy.