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Dorian Gray
Veteran Member
 
Join Date: May 2005
Location: Paris, France
 
2006-03-24, 14:40

Despite frequent assertions that faster disks reduce battery life, the difference is so slight that it's pretty irrelevant. A 2.5-inch hard disk accounts for only a small fraction of a notebook's total power consumption, so even if the power consumed by the disk were dramatically reduced it wouldn't have a big effect on battery life. And the power difference between 5400 and 7200 RPM disks is just a fraction of one watt. Even if battery life is very important to you, you shouldn't choose a hard disk based on power consumption. It just doesn't matter.

A hard disk's overall speed depends on a few things, in declining order of importance: data transfer speed, average rotational delay, and average seek time. The data transfer speed depends on two factors: data density and rotational speed. If the disk is higher capacity, it will also have higher data density, resulting in faster transfer speed. So in the case of the two disks you're considering, the 7200 RPM disk has a higher transfer speed than the 5400 RPM disk, but not by as much as the rotational speeds would suggest, because the slower disk has higher data density (think of more 1s and 0s passing the heads per second as the disk spins because they're closer together). The actual data transfer rate would be about 11% higher with the 7200 RPM disk.

Seek time (the time for the read/write heads to move to the correct track) will be almost identical for both drives, therefore not important. However average rotational delay (latency - the time the heads have to wait before the rotating platter does part of a revolution so the heads can start reading the appropriate data) will be about 33% lower for the 7200 RPM disk. This means that the 7200 RPM disk will start transferring data an average of 1.4 milliseconds sooner than the 5400 RPM disk when the computer asks for data. This difference is not important in typical usage.

So it boils down to whether you want 20% extra capacity or 11% extra speed. Personally I think I'd choose the extra capacity because capacity is a bigger problem for me (with notebook disks) than speed. If you do a lot of disk-intensive work (uncompressed video, Photoshop, etc.) you may value the extra speed more than the extra capacity. For me, the value of a notebook drops if I have to keep data on an external disk - there's a lot to be said for having a big enough disk to keep everything in one convenient place. Of course if you can fit all the data you need on the 100 GB disk you can have the best of both worlds: high speed and enough space. But it's very easy to underestimate the space you'll need.
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