Solid State Drives, or SSDs for short, are quick and silent while sporting lower power consumption and heat generation than a traditional hard disk. What's not to like? Well, they're currently much more expensive per GB of capacity.

As such all but the richest PC builders quickly realise a two-drive solution is necessary, with the quick but small SSD reserved for their operating system and applications only, leaving a hefty traditional hard disk for storing their photos, videos, documents, emails and other personal data. Until SSDs fall significantly in price, the big question then becomes how small an SSD can you really get away with as a boot / application drive?

To find out I sourced a 60GB Agility 2 SSD drive from OCZ which represents the mid-range of SSDs, without compromising on performance and longevity. HD Tach measured average read and write speeds of 202.3 and 197 Mbyte/s with a burst speed of 236.1 Mbyte/s. This ranks it below the very fastest SSDs, but still way ahead of a traditional hard disk, performance which was reflected in swift OS and application startups.

I installed Windows 7 Ultimate 64 bit, followed by Adobe CS5 Production Premium, Microsoft Office 2007 Ultimate, Dreamweaver CS5 and a selection of utilities including Skype, Winamp, Spotify, Adobe Reader, SmartFTP, VLC Player and the Flickr uploadr.

The original bare drive after formatting offered 55.7GB of storage. After installing the OS and applications, but before any updates had been applied, the installation measured 48.2GB, leaving 7.5GB free. It doesn't sound like much, but it's more than 10%, and unlike traditional hard disks, the performance of an SSD doesn't reduce towards the limits of its capacity.

Considering I'd relocated the documents, photos, music and emails to a separate hard disk, I thought I'd got away with a 60GB boot and application drive, but within a few minutes Windows started downloading and installing 'critical' updates. The applications soon followed, with CS5's first update actually requiring an additional 1.1GB of space. These hefty updates barely scratch the surface of multi Terabyte hard disks, but are serious cause for concern on a compact SDD. Within a few days, my 60GB SSD actually had less than 1GB remaining and I began to feel uncomfortable.

I was relatively happy having 7.5GB free, but less than 1GB is too tight for comfort, so I switched to a 120GB Vertex 2 SSD, again from OCZ; the Vertex 2 represents the company's performance series and has become one of the most popular SSDs around. HD Tach measured average read and write speeds of 231.8 and 217.6 Mbyte/s with a burst speed of 237.9 Mbyte/s. The average read and write speeds were roughly 10% quicker than the earlier Agility 2 drive, which will delight performance enthusiasts, although it actually only makes a fractional difference in OS and application speeds.

Freshly formatted, the drive offered 111GB of capacity. I installed exactly the same OS and applications as before so unsurprisingly found the drive just under half full. Several weeks of patches later the drive still had around 60GB remaining, which is plenty of room for installing future applications and updates. I'd say it's the perfect size for my workstation, so long as I have a separate hard disk or RAID array for personal data.

That's not to say a 60GB drive is totally impractical though. I redeployed the 60GB Agility 2 drive in a less demanding office system which employed Windows 7 Home Premium, Adobe CS4 Production Premium, Office 2007, Dreamweaver CS3 and a handful of utilities; again I kept the documents and personal data on a separate hard disk. This time though I was careful to only install the components I really needed on this system, skipping little-used applications in the suites and redundant clip art or templates. Following a series of updates the 60GB drive reassuringly had 22.7GB remaining - roughly one third free, which again is plenty for future updates or selective application installs.

During my tests with both SSDs, I was impressed by the performance boost they offered over a traditional hard disk with the OS and applications starting much faster. I'd definitely recommend an SSD for those who desire snappier performance, although almost all of us will need to supplement them with an additional hard disk for storage of personal data.

As for the crucial question of capacities, I'd say a 120GB drive is comfortable for most workstations which are supplemented by a separate hard disk, although hardcore gamers or anyone who wants their personal data stored on an SSD will need to go for something bigger.

If you only need a handful of applications though and can be fairly strict while installing them, you may get away with a cheaper 60GB drive. OCZ's Agility 2 series is also a great choice for such price-conscious installations, as while they're technically not as quick as the Vertex 2 in benchmarks, most people will be unable to notice much difference in actual real-life use. So if you were yearning for an SSD, but were held back by the high price of larger or faster models, you may find yourself pleasantly surprised by a relatively compact, mid-range drive.