Buying a hard drive used to be simple. You'd find the three or four highest capacity drives you could afford, pick the fastest, and, well, that was it - just a few minutes online would be enough to locate some great products.
These days, though, it's a little more difficult, as you've two very different technologies to choose from. And so before you go shopping, you need to consider a very fundamental question. Conventional hard drives (HDD), or solid state drives (SSD): which is best?
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SSD vs HDD: HDD technology
Standard HDD drives contain multiple disks called platters, which are covered in a magnetic coating and then rotated at high speed. Drive heads then move across the platters, changing the magnetisation of the material beneath to record data, or reading its state to return the stored information.
While the core HDD ideas are simple enough, allowing manufacturers to produce high capacity drives at very low prices, they do pose several problems.
Both reading and writing data requires a lot of work, for instance. Heads must move around, and the platter must spin to exactly the right point before the drive can do anything. This all takes time, and is why hard drives are one of the major performance bottlenecks in many PCs.
Having to move all these components around also means there's a constant power drain, an issue with laptops and netbooks.
And the drive heads gets incredibly close to the platter - a tiny fraction of the thickness of a human hair - so if there's a shock at the wrong time then the two may collide, damaging the drive and losing data. Drive manufacturers employ a range of technologies to prevent this from happening, and as a result these head crashes are rare, but they can't be ruled out entirely - there's always some risk.
You don't have to live with these issues, though: SSD technology can address them all, though at a significant price.
SSD vs HDD: The SSD alternative
Solid state drives (SSDs) take a very different approach to data storage.
They ditch the platters, the heads, all those fast-moving components which cause such problems, replacing them with something much simpler: memory chips. The exact type of chips vary, but most drives use flash memory (essentially the same technology that's used in cameras, MP3 players, memory cards and more) which is able to store data even without any power.
This technology can be expensive, and means SSD drives generally have low capacities and high prices.
But by way of compensation you do get excellent performance. A standard hard drive may take several seconds for its platters to reach full speed, for instance: SSDs are always ready to go immediately. And an SSD doesn't have to move its head around, or wait for the platter to reach a particular point before it can read data, so its access time can be 50 times faster than a regular drive.
SSD read and write speeds are much closer to HDD technology, though, so the overall performance gain won't be nearly so spectacular. Still, equipping a PC with a solid state drive could easily halve the time it takes to boot the system, and that's a benefit worth having.
Other SSD advantages include excellent shock resistance (you're not going to lose data just because you drop one). They're also silent, and lighter than their HDD cousins.
And SSDs have very low power consumption, especially when idle or reading data. The hard drive is responsible for only a small fraction of total power use, so this may only extend laptop battery life by 5 or 10 minutes, but, again, even that could be a benefit worth having.
HDD vs SSD
When you look at the two technologies, then, it's clear that solid state drives are technically superior in many areas. But there's a problem: they're also expensive, and with much lower capacities.
Right now, for instance, you can buy two terabyte HDD drives from as little as £87 (read our reviews of the five best 2TB hard drives).
Spend the same amount of cash on a solid state drive, though, and you'll get only around 3% of that capacity: 64GB, at best. Higher capacity drives are available, but they're prohibitively expensive: a 480GB model, say, might cost you close to £1,000.
Unless you have unlimited funds, then, your first drive for a desktop should always be a standard HDD model. Prices are incredibly low - you can buy a budget 750GB drive for under £30, say - and while the performance may not be up to SSD standards, it'll be adequate for most tasks, and the money you save can give you a more significant speed boost when used elsewhere (you might buy a faster CPU, for instance).
If you're looking to optimise an existing desktop, though, then an SSD can be very useful. The idea is that you buy a fast 40GB drive for under £100, where you'll install Windows, while your data and applications are then installed on a regular hard drive.
You'll then benefit from faster boot times, and a general speed boost as Windows components are loaded more quickly. And while your SSD is small, it'll still have the space to install one or two drive-intensive applications - games, say - to ensure they deliver the fastest possible speeds.
And of course SSDs can be particularly welcome in laptops, although this does depend on what you intend to do with them.
If you're planning to buy a laptop as a desktop replacement system, something that will run lots of applications, then again an SSD probably won't have the capacity to help.
But if you're building a simple laptop to satisfy only basic needs - browsing, email, word processing, say - then a 64GB SSD could be sufficient. And it actually begins to look like something of a bargain.
The drive will improve your system's performance, reduce noise and weight, and increase battery life, if only by a few minutes: not bad for something with a price tag of under £100. See our guide to the 12 best SSD drives to find out more.