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1TB and 5400 tpm: Western Caviar Green vs Samsung EcoGreen
by Marc Prieur
Published on February 26, 2009

For a long time we hadn't seen any 5400 rpms but they have now made something of a come back. Western were the first to signal the return with its Caviar GP range launched in 2007, when it chose to make a virtue out of what had previously been slightly shameful.

However, the first tests showed that performances weren’t that far behind the 7200 rpm models and this with a significant advantage in terms of lower sound levels and energy consumption.

Not necessarily cheaper than their 7200 rpm equivalents, these 5400 rpm drives are an alternative with advantages and disadvantages that we’re going to analyse by looking at the ranges of two manufacturers, Western Digital and Samsung.
The influence of rotation speed
Rotation speed has a direct impact on performance, both in terms of throughput and access times. In terms of throughput, it’s relatively simple: 4 rotations at 7200 rpm take the same time as 3 at 5400 rpm, a net gain of 33% in terms of throughput in theory, on same-density platters. Of course, although at the moment 5400 rpm drives use comparable densities to 7200 rpm drives, in time the 5400 rpm drive may well become denser, which would counterbalance the gain in throughput.

Rotation speed also has an impact on hard drive access times. To gain access to data, first the reading head has to get itself onto the right track on the platter, something that is not linked to rotation speed: this is what manufacturers usually call access time on their spec sheet.

However the head still needs to access the right piece of data, which might be further down the track. So you have to wait ¼, or ½ or whatever turns for the read head to be above the piece of data it’s looking for. This is what is known as latency, and the value given normally corresponds to ½ turn: 5.55 ms at 5400 rpm, 4.17 ms at 7200 rpm, 3 ms at 10 000 rpm.

Therefore, if all else is equal, a 5400 rpm drive will have a shortfall of around 1.38 ms in terms of access time in practice. Not a huge amount obviously, but to be taken into account all the same.
Perfect for some types of use
5400 rpm drives are a good choice for several types of use. The first, of course is for a machine that doesn’t need the highest performance but a significant storage capacity and good environmental spec, such as a Home Cinema PC. But they will also serve well in a NAS.

They also have their place within a high-performance PC, as a secondary storage facility. You could for example use a VelociRaptor, or even an SSD, for your everyday applications and a 5400 rpm for your data: your holiday Blu-ray and the 100 daily photos of your youngest can easily be stored here!

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