SSDs have cornered the market for high-performance system drives, relegating their mechanical counterparts to secondary storage. Traditional hard drives are simply too slow to keep up with the flash-based alternatives that have taken the PC industry by storm.
That said, mechanical drives still have an undisputed claim to the mass-storage crown. Flash memory's blistering performance comes at a price—literally. Even after years of falling flash prices, solid-state storage still costs a lot more per gigabyte than traditional hard drives. Mechanical drives are also available in much higher capacities.
Seagate's Desktop HDD.15 is a perfect example. This latest addition to the mechanical field squeezes four terabytes into a single 3.5" case. It's also eminently affordable. You'll pay just $190 for the thing, which works out to a nickel per gig. The per-gigabyte cost of even budget SSDs is an order of magnitude higher.
The Desktop HDD.15 is the most affordable 4TB hard drive on the market, which isn't too surprising. While the competition spins its platters at 7,200 RPM, the HDD.15 has a slower 5,900-RPM spindle speed.
Slower rotational speeds are nothing new on the desktop; low-power "green" drives have employed them for years. We typically see slower spindles used to bring up new platter technologies, and that's exactly what's happening here. The Desktop HDD.15 is the first four-disc implementation of Seagate's terabyte platters.
The platters have an extremely high areal density of 625 Gb/in². Their individual tracks measure 75 nm wide, or about a thousand times narrower than the average human hair. Accessing data on such a small scale is no easy feat, especially given the speeds involved. At 5,900 RPM, the outer edge of the platter is moving at the equivalent of 61 miles an hour. Increasing the rotational speed to 7,200 RPM boosts the outer-edge velocity to 75 MPH. No wonder drive makers usually start new configurations at a slower speed.
Of course, even low-speed hard drives need to be incredibly precise. Because there's so little room for error, environmental vibration can interfere with normal operation, causing the drive head to drift off-track or dangerously close to the surface of the platter. The Desktop HDD.15 features AccuTrac servo tech to maintain read and write performance in what Seagate describes as "high-touch" environments. An all-in-one system pumping music through built-in speakers is provided as one example of such an environment. The product guide also suggests the HDD.15 is ideal for desktop RAID and NAS applications, both of which entail ambient vibration due to the close proximity of other drives.
OptiCache describes the dual-core storage processor and associated technologies that blanket most members of Seagate's Desktop HDD family. The ARM-based chip is fabbed on a 40-nm process, and it's infused with improved caching algorithms that work in conjunction with 64MB of DRAM memory. This is a straight-up mechanical drive, so there's no NAND involved.
|Spindle speed||5,900 RPM|
|Average data rate||146MB/s|
|Max sustained data rate||180MB/s|
|Idle acoustics||2.3 bels|
|Operating acoustics||2.8 bels|
|Typical operating power||7.5W|
|Warranty length||Two years|
The Desktop HDD.15's slower spindle speed produces lower average and maximum sustained data rates than those of Seagate's 7,200-RPM offerings. Those drives stack as many as three of the same terabyte platters, and they're rated for an average speed of 156MB/s and sustained peak of 210MB/s.
The performance of mechanical drives usually hinges on the combination of spindle speed and areal density. However, other factors clearly influence the Desktop HDD.15. The drive spins its platters 18% slower than Seagate's 7,200-RPM desktop drives, yet its average data rate drops only 6%. The HDD.15's maximum data rate is 14% lower, which is closer to what we'd expect given the difference in spindle speed.
We'll examine actual performance in a moment. First, I have an axe to grind. The Desktop HDD.15's warranty coverage runs out after two years. That doesn't mean the drive will spontaneously combust when the term expires. However, the relatively short coverage doesn't inspire confidence in a product that will store four terabytes of precious data. It wasn't too long ago that all of Seagate's internal hard drives had five-year warranties.
Ok, so it was about 4.5 years ago—pretty much an eternity in the PC industry. If you want a 4TB drive with a five-year warranty today, you have to spring for the WD Black, which rings in at $300. Speaking of the Black, let's move on to our comparative performance tests.