You might be focusing all your effort on developing low-power systems by concentrating your efforts on your system’s logic board. Did you stop to consider that you can also find a quick way to cut a lot of power consumption by re-evaluating your choice of peripherals? Here, I’m specifically writing about hard disk drives (HDDs). Many embedded systems, and larger systems, incorporate rotating, mechanical disk drives. Both IDE/PATA and SATA HDDs are increasingly common in all sorts of systems including many embedded designs. Your designs might use either type. I’ve just spent the last three days attending the Flash Memory Summit and the theme of the day and of the year was solid-state drives (SSDs)—assemblages of semiconductors that emulate HDDs at the interface level so that they can plug into existing interfaces in most systems. SSDs can replace HDDs in many cases and save you Watts of power.
Here’s where a bit of digression is in order. The HDD industry has hit bottom on cost, resulting in the $30 HDD, as explained at the Flash Memory Summit by Sun Microsystems’ Lead Technologist for Flash Memory, Michael Cornwell. The $30 HDD has one platter and one head. It’s the cheapest thing the HDD vendors can make. It rides the bit-density curve and whatever fits on one platter at any given time is what the capacity is. It costs $30 (hence the name).
Lots of embedded products use this cheap HDD for secondary storage. The $30 HDD’s capacity is presently 120 Gbytes, which conveniently works out to 25 cents per Gbyte of storage. However, HDD capacity never stands still. The industry has a consensus road map for improving HDD density 10-30x and the $30 HDD will ride that curve like all of the more expensive HDDs. They will still cost $30.
SSDs of equivalent capacity cost more than $30. A lot more. And they will for a while. While many industry pundits predicted a crossover in cost per Gbyte last year when NAND Flash prices were dropping like a rock, the picture is quite different this year. NAND Flash prices aren’t falling nearly so fast so the pundits are saying (this year) that SSDs will never reach price parity with equivalent-sized HDDs.
For a lot of products, that smaller drive capacity doesn’t matter. For many products, 120 Gbytes of capacity is already way too much and yet that’s the smallest HDD increment you can get today. Not so with SSDs, which are based on NAND Flash chips, not spinning platters. For example, you can get IDE/PATA and SATA SSDs from SanDisk in capacities from 8 to 64 Gbytes. If those capacities work for your design, then you’ll like the power consumption: 0.5W typical, 0.15W average (typical), and 15mW in sleep mode. If the smaller capacities work for your design, you can also save money because at least some of those SanDisk SSDs cost less than $30. Also note that an SSD wakes up much faster than an HDD, so a sleep mode spec has considerable value in many applications.
Switching from an HDD to an SSD may be a very easy way to carve out some power consumption from your design. As an added bonus, the SanDisk drives are even smaller than a conventional 1.8-inch HDD, so you can carve some cubic millimeters from your system design and you can save on BOM cost as well. SSDs have a lot to commend them and merit consideration in your design.
