Hard Disk Drive Question

1. SATA is one type of interface between a hard drive and its controller on the mobo. It is by far the most popular interface right now and will continue for some time to come. The name stands for "Serial ATA", and the "ATA"part means "AT Attachment". The "AT" part there is because the earliest introduction of that type of HDD interface system was in the old IBM AT computer design. (The older interface system that SATA replaced is called IDE or PATA for Parallel ATA.) The numbers are the maximum data transfer rate of the interface system itself. The first SATA system could communicate with the mobo at a max rate of 1.5 Gb/s (Gigabits per second). As a ROUGH approximation allowing for data validity check overheads, etc, the conversion from bits to Bytes in this area is a factor of 10, so that same interface rate is sometimes called 100 MB/s (note the capital B for Byte). The second iteration of SATA doubled that data rate max to 3.0 Gb/s or 300 MB/s. It was called SATA II. The latest versions doubled that again to 6.0 Gb/s, and abandoned the Roman Numeral label system. So now the "proper way" to label these last two is SATA 3.0 Gb/s and SATA 6.0 Gb/s.

Those speed ratings have led to confusion. It turns out that, for common hard drives with rotating disks and moving heads inside, the mechanical components cannot access the data that fast. The fastest actual data transfer rates for sustained periods is about 150 to 180 MB/s for mechanical hard drives - more than the communication rate for the first SATA, but still less than the rate spec for SATA 3.0 Gb/s. So why did they make that one, and then another even faster? Because they were planning for faster types of storage devices like the new Solid State Drives - SSD's. Since these have no moving parts, they CAN move data close to the communication rate max for SATA 3.0 Gb/s, and a few maybe even faster now. More speed to come, we dream.

2. RPM is simply the rotational speed of the disks inside the unit. As a simple general rule, faster is better because it takes less time for all the data in one "track" on one platter to pass under the stationary head and be read. However, there are trade-offs. Rotating faster uses more power to drive the motor. Hence it is common to use 5400 rpm units in laptop machines and in low-power-consumption "green" drives. The common desktop units are typically 7200 rpm, although there are labels like "intellipower" and so on that actually mean the rotation rate is varied, depending on the workload, but not likely to exceed 7200 rpm. There are HDD units working at 10000 rpm and higher, and they do move data faster. However, they certainly use more power and their internal construction must me much heavier and precise, so they are much more expensive and typically do not come in the very high capacities of 7200 rpm units.

These rotational rates have an impact on HDD performance, but how much depends on the type of use. For simply finding and opening one program there is a small impact. Heavy use for constantly reading and writing data in long continuous files shows the most impact from rotational speed. Heavy use for lots of reading and writing of many small data chunks located randomly all over the unit is less impacted by this speed, and is affected a lot by the head movement speed.

3. A Buffer is a chunk of RAM mounted on the circuit board of the HDD unit. The plan is this: when data needs to be read, the HDD's own on-board control system moves the head arm to the right place and reads data from the disk surface until it finds the start of the Sector it needs. The, instead of reading only that one sector, it reads many in sequence - up to a whole track right around in one platter rotation - and stores it in the on-board buffer RAM. The control board then feeds out to the mobo only the particular data that was requested. However, the bet is that the next data request will be for the next chunk of data from that same file, and it will already be in the buffer RAM. If that is true, the data can be fed out immediately, rather than trying to find it on the disk. When this works out, the process speeds up the HDD performance. The same types of process can be used for writing data - store it first and wait until a lot of data is ready to write in one continuous operation. Of course, the more RAM you have on the HDD's board, the more performance improvement you get. As a rough rule of thumb, 8 MB is pretty small for this job, 16 MB is better, 32 MB will show up better yet, and 64 MB will be a small improvement over that. One combination you will see is "green" drives at 5400 rpm (a little slower in data access) with 64MB of on-board buffer RAM to boost that performance to offset the rotational speed thing. Such combos are certainly better than green units with little buffers, but not as fast as 7200 rpm units with 32 or 64 MB or buffers.

4. A hybrid drive is a mechanical HDD unit that also has on board a Solid State Drive unit. To the outside world this appears to be one "drive", but it acts like it has a huge buffer - the SSD part is MUCH bigger than 64 MB - and so its performance is much better than a unit with HDD only.

5. A drive that has been Refurbished and Recertified is one that was used and developed a failure. It was returned to the manufacturer (or some third party shop), diagnosed and repaired, then tested to ensure it meets the original performance specs for a new HDD. These units are sold cheaper than brand new drives because they already have proven themselves less reliable than most new drives - MAYBE. The repair could have been perfect, and the unit will perform and last just as well as a new HDD. But maybe not - you cannot know for sure. For this reason, most of these have shorter warranty periods than new HDD's.