Last month, I believed that Western Digital was still the only vendor manufacturing 2-Tbyte, 3.5-in. hard-disk drives in high volumes (see “Western Digital packs 1 Tbyte into 2.5-in. disk,” EDN, Aug 20, 2009, pg 13). As it turns out, I wasn’t exactly right; Seagate recently began selling a 2-Tbyte member of its Barracuda LP family, which the company unveiled in April. Seagate’s ST320005N4A1AS-RK, a four-platter, eight-head configuration, spins at 5900 rpm. Western Digital, conversely, doesn’t specify a rotation-per-minute performance metric for its four-platter WD20EADS, instead relying on a nebulous “IntelliPower” marketing moniker. The IntelliPower algorithm dynamically varies rotational speed to optimize performance versus power consumption at any time.

As for faster-rotating, 2-Tbyte variants, Seagate is still not shipping its previously announced 7200-rpm drive. Hitachi, with its recently announced $329 Deskstar 7K2000, is the first to reach that vaunted threshold. Whereas the competing drives are four-platter models—that is, 500 Gbytes/platter—the Deskstar 7K2000 is a five-platter, 400-Gbyte/platter, 10-head configuration. Hitachi squeezed this abundance of magnetic media into the 3.5-in. form factor’s standard 1.028-in. (26.1-mm) height. However, as with Hitachi’s four-platter, 1-Tbyte hard-disk drive that it unveiled in early 2007, you should expect the Deskstar 7K2000 to on average burn more power than a future equivalent with fewer platters, with all other specs being equal.

What’s with the platter-count discrepancy between manufacturers? Think about it: As a platter spins ever faster, it becomes increasingly challenging for the read/write head to discriminate between sequentially stored data bits. That difficulty is fundamentally the reason that Hitachi’s 7200-rpm drive needs five platters to deliver the same aggregate capacity as Western Digital’s and Seagate’s slower-spinning four-platter competitors.

PMR (perpendicular-magnetic-recording) technology and other techniques over time enable disk-drive suppliers to squeeze ever-increasing bit counts onto a given-sized sliver of magnetic media. The same press release that launches the Deskstar 7K2000 provides a hint about where Hitachi will shortly be going, stating that, in addition to the new drive, Hitachi is refreshing its high-volume desktop-hard-drive family. The new 7200-rpm Deskstar 7K1000.C family will deliver as much as 500 Gbytes per platter and will come in capacities of 160 Gbytes to 1 Tbyte. Volume production of the new Deskstar 7K1000.C will begin this quarter.

This article originally appeared as an entry in the Brian's Brain blog. Click here to view that entry.