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Desktop HDDs: Differences

Tom’s Winter 2008 Hard Drive Guide
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Hard drives are storage devices based on rotating magnetic media and differ in various respects—the important being the recording technology used. These days, all manufacturers utilize perpendicular magnetic recording technologies (PMR), which means that the alignment of magnetic domains is now vertical. Hard drive makers switched from longitudinal to perpendicular recording to avoid magnetized elements influencing each other, a phenomenon known as superparamagnetism. This allowed recording densities to be increased considerably, a trend that will continue. Hitachi forecasts that in the coming years, the traditional 3.5” form factor will store up to approximately 50 TB using patterned media and heat-assisted recording.

Platter Count

Other important hard drive parameters include the spindle rotation speed, interface, cache size, and the number of platters used. All high-capacity 3.5” desktop hard drives are based on several platters and enterprise units often have several as well; 2.5” notebook hard drives usually only use one or two platters due to space constraints and the need for robustness. Most terabyte drives are based on three platters today, including the Hitachi Deskstar 7K1000.B, Samsung Spinpoint F, Seagate Barracuda 7200.11, and WD Caviar series—while the first generations of terabyte hard drives required up to five platters (such as the Hitachi Deskstar 7K1000). The current capacity champion, Seagate’s Barracuda 7200.11 at 1.5 TB, reaches its capacity point using four platters.

You can find out the platter count by looking at the number of heads, which is always listed in a hard drive’s data sheet. Every platter requires two read/write heads: one for the top and another for the bottom. Eight heads, for instance, means that there are four platters.

Spindle Speed

Most fast desktop hard drives use a 7,200 RPM spindle speed. Some low-power options, such as the WD Caviar Green series or the Samsung Eco Green drives, spin at a reduced 5,400 RPM rotation speed, which introduces power savings at the expense of performance. However, a modern and well designed 5,400 RPM drive may very well compete with an average 7,200 RPM drive. Clearly, it’s important to always go for the most recent product, to be sure you get the best bang for the buck.

An important drive to mention in the context of spindle speed is Western Digital’s Raptor family, which has thus far been the only 10,000 RPM desktop hard drive. The first-generation models, with capacities of up to 150 GB were based on the 3.5” form factor, while the latest product, the Velociraptor, is a 2.5” drive meant to also fit into the entry-level enterprise segment. While the Velociraptor is the fastest mechanical desktop hard drive, the older versions are only faster than modern terabyte drives when it comes to I/O performance and access time. Throughput is higher on any of the mainstream 7,200 RPM 3.5” drives today.

Negligible Details

Drive manufacturers and PC vendors sometimes advertise the cache size of a hard drive: 32 MB currently is the largest cache size right now, 16 MB can be considered the de-facto standard, and some lower-capacity drives still come with only 8 MB of cache. It’s worth noting, however, that we looked at the difference between 8 MB and 16 MB cache in 2007 and found no significant difference.

The drive’s interface is another technical detail that is almost negligible. Nearly all desktop hard drives are based on Serial ATA/300, while notebook drives utilize SATA/150 or SATA/300. Since desktop hard drives have not even reached 130 MB/s in throughput, even SATA/150 would be fast enough for all models currently available. SATA/300 makes sure that cache throughput is maximized, but it does not make a noticeable difference in everyday use. So go ahead and attach a SATA/300 drive if you only have a SATA/150 controller—it won’t introduce a serious performance penalty today. Making the jump to SSDs, of course, puts more of an emphasis on interface.

Cost And Warranty

Warranty is not only important for getting a replacement in case of drive failure. Because you intend to use your new hard drive for several years, and we’re talking about rather high capacities of a terabyte or more, a solid warranty creates confidence. We wouldn’t want to spend money on a 1.5 TB hard drive that comes with a poor one or two year warranty. Fortunately, all hard drive makers provide at least three years’ warranty for their retail products. All premium desktop drives, as well as all enterprise drives, are backed by a five-year factory warranty. This applies to Seagate’s Barracuda 7200.11 family and to the Western Digital Caviar Black series as well.

Be careful if you purchase an OEM drive that wasn’t intended to be sold separately: these may be covered by shorter warranties.

Finally, we recommend checking the cost per gigabyte once you select your hard drive type. If you don’t really need a full terabyte of storage, you can save money if you go for a “sweet spot” capacity. Most likely, the 750 GB or 640 GB version of the desired drive offers a better cost per gigabyte than the terabyte top model.

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