Although it goes without saying, a 250 GB HDD is cheaper than a 320 GB one. However, there is a concept called price per gigabyte. The PPG represents the price you pay for 1 GB of data and it differs over different capacities and to a small extent over different models having the same capacity. For example, a 250 GB SATA HDD costs around Rs 2,100, while a 500 GB costs Rs 3,900. A 750 GB HDD costs around Rs 6,200. Given these three figures let's look at how we calculate the price per GB:
•For a 250 GB hard drive: Cost per GB = Price I Total size of
HDD = 2100 I 250 = Rs 8.4 per GB
•For a 500 GB hard drive: Cost per GB = Price I Total size of HDD = 3900 I 500 = Rs 7.8 per GB
• For a 250 GB hard drive: Cost per GB = Price I Total size of HDD = 6200 I 750 = Rs 8.26 per GB
• Lower the better.

If you look at the above calculations, you will notice that a 500 GB drive has the best price per GB value. Although a 250 GB hard drive is cheaper, the per-GB cost is higher. This is also evident from the fact that the 500 GB drive has double the storage space at less than double the price. The 750 GB cate¬gory offers better value for money than the 250 GB hard drive, but its price per GB is higher than the 500 GB drive. This is an important calculation that you should do yourself each time you go storage shopping. The same formula can be applied to notebook and external HDD solutions. Also keep in mind that the size category which offers the best value for money keeps changing. A few months from now we could well see 750 GB HDDs offering the best price per GB in the desktop segment.

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Another important specification that you should update yourself on, is the number of platters that the hard drive has. The lesser platter an HDD has, the cooler and faster it runs. These days, the areal density of platters has reached the mag¬ical 320 GB mark. This means that unlike older HDDs which needed 4x 80 GB platters to allow 320 GB of storage, the latest HDDs make do with a single platter. Less mechanical parts means lower heat generation, thereby improving reliability and performance with a favourable effect on price to boot.