I'm curious to know how many platters, heads, cylinders are in some of the popular consumer drives, but I could not seem to locate this info in the specification sheet. For example, the WD Blue spec sheet here () does seem to have this info. Why is this not included in the spec sheets, and where might I find this info, if it can be found at all?
2 Answers
A typical consumer hard drive may have anywhere from one to five platters. The weight of the drive is often a good indicator of the number of platters used.
Most new desktop hard drives with 1 TB or lower capacity have only one platter to reduce cost. As more platters are added onto the drive, drag and turbulence from the air inside the drive become an increasingly significant issue, which is why consumer hard drives top out at five platters.
Most laptop hard drives use no more than two platters, although the Seagate/Samsung Spinpoint M9T uses three platters to achieve a 2 TB capacity without exceeding the 9.5mm z-height limit for most laptops. Drives of 500 GB or lower capacity typically use only one platter. Thin drives with 7mm or 5mm z-height are limited to one platter.
Although these are not consumer hard drives, the helium-filled HGST Ultrastar HelioSeal drives use seven platters (7Stac™). Because helium has significantly lower density than air, there is less turbulence on the platters, reducing power consumption and allowing more platters to be used. These drives are designed for use in datacenters where storage density and power are critical.
All of the WD Blue drives on the spec sheet you linked to have one platter. Compare with the WD Green drives on this spec sheet (ignore the NPVX models which use the enterprise 2.5" 15mm z-height form factor); the 5 TB and 6 TB models have five platters while the 1 TB and 500 GB models have one.
Cylinder count is no longer relevant; modern hard drives store more data on outer tracks of the hard drive than on the inner tracks. Cylinder-head-sector addressing is obsolete and has long been replaced with logical block addressing.
I also noticed this change a few years ago. I believe there was a correlation in the minds of consumers between higher platter counts and lower drive reliability. I think the actual problem was people using high capacity consumer grade drives with large platter counts without vibration compensation and reduction features (WD Green for example) in NAS systems, causing the high failure rates.
The solution of course was to hide the platter count from the consumer, so that was no longer a part of their purchasing decision, and to make drives specifically for NAS systems.
The concept of a cylinder is not really relevant to modern drives using LBA addressing, which is pretty much any drive still functioning. For determing the platter and head quantity, sometimes those can be extrapolated using the drive weight and the sustained performance numbers for a given family of drives, but you need a basline for that to work.
The best option is to contact the drive manufacturer, or to open up some drives and look.
