You have come a long way, HD

Samsung's recent announcement of a 1TB disk at the $200 price point provides a dramatic illustration of just how rapidly the cost per unit of storage continues to fall. When 1TB hard disks were first introduced, in April of 2007, they launched at a cost of $400 at retail, and have fallen steadily in price since then, reaching $200 this month, halving in price in only a year to $.20 per gigabyte. This rapid decrease in price is part of a trend which spans the whole of the technology's history; the price of disks has fallen by a factor of 35,000 in the last 17 years.

At the launch of the 1TB hard disk, and through the tier's life so far, other disks have been available with lower costs per gigabyte and per transfer speed. In April 2007, 500GB disks had just hit $100, the $.20 per gigabyte level 1TB drives are just now reaching, and now 750GB drives can be had for $.16 per gigabyte. However, the cost of additional drives, in controller channels, server space, and electrical power, makes the highest-capacity hard disks optimal in all but extreme cases, and their price the relevant metric.

All roads lead to SSD
Other notable trends are at work in disk development. As capacities have risen, transfer speeds have risen and latencies have fallen, but not nearly as fast. A 1991 40MB Maxtor IDE disk was recently benchmarked reading at 0.6 MBps, whereas a modern 1TB disk may surpass 100MBps, a 160-fold improvement. Their capacities, however, differ by a factor of 25,000; the time to copy a complete disk rose from less than one minute to more than three hours in those same 17 years.

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