Everyone is talking about SSDs replacing hard drives, if not today than Real Soon Now. On the surface, solid state drives have a lot going for them: no moving parts, potentially very dense storage, and the possibility for low power consumption. The main things stopping me, at least, from seriously considering an SSD in my machines until recently were price and capacity. The cheapest SSDs cost something like $600 for 64 gigabytes: a normal hard drive might costs $200 for 500 gigabytes of storage, making SSDs easily ten times the price of mechanical hard drives on a per gigabyte basis.

But solid state drives obviously have an advantage in terms of reliability and power consumption, right? So all I have to do is wait for the inevitable drop in price/increase in capacity that Moore’s law suggests and I’ll be set. Maybe… or maybe not.

The first myth is the one around reliability. Yes, solid state hard drives lack moving parts, and fewer moving parts means fewer things to break down. But the technology behind solid state drives today relies upon components that have a limited number of write cycles. Until recently, using an SSD for something like a Windows swap file, which changes very rapidly, was basically a death sentence for the device. Current drive technology overcomes the write cycle limitation by having redundant components and automatically “disabling” bits that begin to fail: this permits something approaching the same write lifespan as a mechanical hard drive.

Tom’s Hardware recently debunked another myth about SSDs: that being that they use less power. The surprise is that solid state drives actually use *more* power than modern hard drives. The logic behind why this is so is that the current SSDs basically are either entirely “on” or entirely “off”: they have no intelligence to only turn on part of the device, or to switch to a low power mode when not being accessed. And newer hard drives have all sorts of energy saving tricks: spinning down the drive, turning off the drive entirely, and head positioning logic that reduces movement (and thus power consumption). The SSD manufacturers say they can overcome their power consumption issues, and I don’t doubt that they can, but it is a surprise none-the-less.

So what advantage do SSDs bring? In *theory*, they could be made much faster than hard drives- however, today’s fastest hard drives are still 20-30% faster than the best commercial solid state drives. In *theory* an SSD could use less power: after all, mechanical devices have to deal with things like inertia and so on. But the hard drive manufacturers have had decades to tweak the power consumption of their devices. And it stands to reason that a solid state device should be more durable than a mechanical device… but the truth is that the SSD technology has its own lifespan issues, even though it may be more shock resistant than a mechanical hard drive.

I guess at the moment solid state drives offer not much more than “potential”. Future SSDs may live up to the expectations people have for them, but if you buy one today you are paying ten times the price for slower, less energy efficient, and arguably less reliable storage. My plan to buy one in a year or so has been set aside: maybe in four or five years the technology will catch up with the potential. Of course I’ll be watching to see how things develop, but it looks like the upgrade drive I was thinking of buying for my MacBook Pro sometime next year will be a normal mechanical hard drive.