No matter how far we have come along in hard drive technology, the hard disk drive is still based on the same old mechanical components as the clunky beasts of yesteryears. It still has a motor, a spindle and bearings, read/write heads, actuator and of course, the platters. All of which are obviously not solid-state in nature.
Rotation Speed – Also known as the spindle speed, this greatly determines the read/write performance of the hard drive. The hard drive has a motor that rotates the platters around a spindle at a fixed speed. The rotation speed is given in revolutions per minute (RPM). The higher the rotation speed, the faster the platter rotates and the faster the drive can read and write data. Of course, it gets exponentially more difficult to ramp up the rotation speed. All desktop hard drives now rotate at 7200 RPM while notebook hard drives can rotate as slowly as 4200 RPM. High-performance hard drives meant for workstation or server use boast rotation speeds of 10,000 RPM or 15,000 RPM, albeit at the expense of noise, heat and storage capacity.
Platter Density – Platter density, also known as areal density, is simply the measure of how many bits of data you can pack into a square inch of the hard drive's platter. Denser platters not only give you a lot more storage capacity, they also increase the read/write speed at any given rotation speed. This is because a denser platter allows more bits to pass under the read/write heads in a single revolution. Hence, for a given storage capacity, it would be better to buy a hard drive with fewer but denser platters than a hard drive that uses less dense platters but has more of them.
Cache – Cache, or the buffer, is memory (usually SDRAM) integrated into the hard drive. It is used to improve the transfer rate of the hard drive by storing some data for much quicker access. The size of the cache determines how much data (in MB) can be stored for quick access. The larger the cache, the better the hard drive will perform, albeit only if the data is stored within the cache. Most desktop hard drives have a buffer of 8MB or 16MB.
NCQ – The Native Command Queuing (NCQ) feature allows the hard drive controller to rearrange read and write commands for maximum efficiency. Instead of queuing the commands in a FIFO (first in, first out) manner, the hard drive controller can rearrange them so that the hard drive's read/write heads do not need to move so much. This not only reduces the stress on the head actuators, it also improves random read/write performance by reducing the random seek times.
Let me stress again that NCQ works best for random reads and writes, which is a usage model seen in servers. It doesn't do anything for contiguous reads and writes, which is what usually happens in desktop PCs. So, it is really a server-centric feature. In fact, it can reduce your hard drive's performance by wasting time queuing the commands and trying to calculate a better sequence.
Interface – There are two major hard drive interfaces for desktop PCs - one being the older Parallel ATA (PATA) or IDE and the other being the newer Serial ATA (SATA). PATA controllers and hard drives are being phased out now, so unless you are thinking of upgrading an old system, there's no reason to continue buying drives using the slower PATA interface. The Serial ATA interface is faster and offers new features like the following :
a) Hot-Plugging : You can attach and remove SATA hard drives without first powering down the PC. Just plug in the SATA data and power cables, and the system will detect and initialize the drive.
b) Dedicated Bandwidth : Unlike PATA which allows two devices to share a single data channel, SATA gives each drive its own data channel. Therefore, each SATA hard drive will not need to share its bandwidth with any other device.
c) Easier Cabling : A standard PATA cable is around 2.5" inches wide while a SATA data cable is only a 1/4" wide. Because the SATA cable is 8X thinner than a PATA cable, it allows for easier and neater cable management. The smaller size also allows for better air flow, indirectly contributing to better cooling performance in your PC.
d) Cable Distance & Flexibility – PATA's parallel signalling method (with 80 conductors) severely limits the length of its cable due to the problems of noise and crosstalk. SATA doesn't have this problem and can be routed up to 1.5 meters from the motherboard. The eSATA (External SATA) standard allows for an further extension of 2 meters without signal boosting and daisy chaining, allowing you to use multiple SATA drives with one eSATA port.