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Hard disks

Posted on 12 May 2008 at 11:24

Like any component inside the PC, hard disks vary in performance. You'll notice a difference between an old model from a few years ago and the very latest, but the variation between recent disks won't be obvious. Even in benchmarks dedicated to disk testing, the separation is a few per cent between the slowest and fastest available. If you're looking for the very best in performance, every little helps, but for most PC users value and capacity are more important, not to mention noise levels.

Although you can still buy hard disks equipped with the old Parallel ATA interface, the vast majority of disk models are now exclusively available as Serial ATA. Where Parallel ATA maxes out at 133MB/sec, the first Serial ATA specification provides 150MB/sec, and the latest SATA/300 controllers and drives can theoretically shift 300MB/sec. In reality, though, the very fastest portions of the very fastest current hard disks can only sustain data rates of just over 100MB/sec, so any of these interfaces would do. In reality, though, your motherboard will probably only offer a single Parallel ATA channel for your optical drive, so Serial ATA is definitely the way to go.

Apart from the sheer size in gigabytes, hard disk specifications usually revolve around the rotational speed in RPM, cache size in MB and access time in milliseconds. Virtually all mainstream desktop hard disks run at 7,200rpm, although enterprise disks aimed at workstations and servers can spin at up to 15,000rpm. Cache sizes, however, vary more drastically, from 2MB right up to 32MB. More is theoretically better, and we'd recommend avoiding the budget 2MB models entirely. Access times also affect performance - the lower the better.

The fastest desktop disk around is Western Digital's Raptor X. This gets its performance from its 10,000rpm rotational speed, which gives it an access time of well under 10ms, where most 7,200rpm drives only offer 13ms or higher. But at over £100 for 150GB, it's hardly cheap, and its long-held dominance is seriously under threat.

The one important performance factor you don't usually see quoted directly in hard disk specifications is how densely the data is packed on each platter within the disk, usually expressed in gigabytes per platter. The more densely packed the data, the faster the disk will be. Samsung currently has the highest with its 1TB Spinpoint F1, which packs 333GB on to each platter, where many hard disks use half that. Not surprisingly, this is also one of the fastest disks you can buy, quicker than the Raptor X in some tests.

Usually, however, the largest hard disks cost a premium, so aren't really such great value from a pence-per-gigabyte perspective. This is currently true of the 1TB monsters that have recently arrived on the market, with Samsung's costing around £160. But 750GB drives are now quite reasonable. We've chosen the 750GB version of Samsung's Spinpoint F1 for our gaming PC. It packs 250GB per platter and isn't quite as fast as the 1TB version, but at £76 its price is right.

When specifying a new hard disk for your PC and your main concern is value, make sure you divide the price by the capacity, as this is the most significant assessment of cost. Using this metric, the cheapest disks almost never give the best value. Just a few quid more could get you a lot more gigabytes. Unless your budget won't stretch beyond £30, we wouldn't recommend a hard disk smaller than 250GB. You get significantly less storage for your money with 160GB models and below, so we went for the 250GB Maxtor DiamondMax 21 in our budget PC.