The SSDs in our latest Labs test are designed as drop-in replacements for conventional hard disks, and in everyday use they should behave just like their platter-based predecessors. After you install one, the biggest changes you can expect to see are your OS and applications loading up more quickly, and file transfers taking less time to complete.
But moving to SSD technology does raise some issues that don't apply to mechanical disks, and before you take the plunge it's important to understand them.
Size and price
Conventional hard disks are cheap. Shop around and you can buy a 1TB drive - big enough to store an entire library of home videos and music - for around $120. So as consumers we tend to buy far more space than we really need.
But, as this month's Labs clearly indicates, SSDs are expensive - typically costing some 30 times as much per gigabyte as an old-style spinning disk. So it's worth asking yourself some difficult questions about exactly how large a drive you need. For desktop systems, you can save a lot of money by choosing a small SSD to hold your operating system and leaving personal data on a secondary, conventional drive. If you're upgrading a laptop, of course, your options are more limited.
On the other hand, you also should be aware that larger drives typically perform better than smaller models (one reason being that a design with more physical chips gives more scope for parallel transfers). It's a good idea to compare the manufacturer's quoted transfer speeds across different capacities before investing, especially if you're considering buying a drive from this month's Labs in a different size to the tested model.
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| Pick your SSD: we've given ratings on 12 SSDs in the July issue of PC Authority |
MLC vs SLC: speed and endurance
The flash memory chips used in SSDs come in two types. Multi-Level Cell (MLC) chips store two bits of data per addressable "cell" on the chip, while Single-Level Cell (SLC) chips store only one bit at each address. SLC chips are faster, especially when it comes to writing data, but since each cell yields only half the storage capacity of an MLC chip, it's twice as expensive to produce. That's why nearly all consumer SSDs use MLC technology. As the market matures over the next few years, though, manufacturing costs may fall enough to make mainstream SLC drives a realistic proposition.
SLC chips have one other advantage over MLC: they last longer, or to be more precise more data can be written to them before they start to fail. Intel's MLC-based X25-M, for example, has an advertised write endurance of 35TB, while the 64GB X25-E, based on SLC technology and aimed at enterprise roles, is good for an immense 2PB of data.
This isn't an issue you need to worry about if you're buying an SSD for everyday desktop use, and most manufacturers don't even cite write endurance figures for their MLC models. But if you're building a business-class server that expects to handle a heavy volume of transactions, it's a reason to be cautious of consumer drives.
Drive geometry
Conventional hard disks are divided up into sectors, tracks and so forth. Such divisions are fundamentally meaningless in relation to SSDs, but these drives are designed to emulate the geometry of a conventional hard disk to ensure compatibility with existing operating systems and software.
It isn't a perfect fit, though, and this has implications if you're migrating your system from a platter-based drive to an SSD. If you simply image your current system onto the new drive, the arrangement of the sectors may not match up properly with the 4KB storage sectors used by an SSD - and that could significantly degrade performance.
Happily, the solution is simple: use the disk tools built into Windows Vista or Windows 7 (or their respective setup routines) to initialise, partition and format your new drive. The OS or installer will automatically align all partitions so that the layout of the file system properly matches up with the internal geometry of the SSD. Yes, this means you'll have to perform a fresh installation of Windows and all your applications; but if you want to get the best from a solid-state drive, this is the way to do it.
TRIM
TRIM is a low-level command issued by the operating system to tell a solid-state drive to erase the data left behind by deleted files. This may sound like an obvious feature, but it's only become an effective standard within the past year or so. Indeed, several of the drives in this month's Labs were originally released without TRIM support, and had it subsequently added through firmware updates.
Without support for TRIM, SSDs will delete blocks of data that aren't needed only when the OS wants to overwrite them. This causes delays to write operations, which get progressively worse as the disk becomes increasingly filled up with the detritus of old files. With TRIM, the OS can instigate "garbage collection" at appropriate times, helping your SSD to maintain peak performance even after years of use.
Happily, almost all of this month's drives support TRIM, and it's certain to be standard on all future models. And since it's built into Windows 7, users of Microsoft's latest OS get the benefit automatically. If you're running XP or Vista, though, you're out of luck.
Conclusion
Performance can only keep improving, and with SATA/600 already starting to appear on motherboards, there's no reason why future models shouldn't achieve double or triple the throughputs offered by current drives. Advances in memory cell technology could make SLC drives more affordable too, bringing their increased write performance and longer lifespans to the mainstream market.
Such changes won't happen overnight, but you've only to look at the CPU and RAM markets to see how quickly semiconductor technology can advance when it's driven by demand. And the rapid evolution we've seen of late in the SSD market suggests that the snowball is already rolling.