Storage technologies as a whole develop year on year at an extraordinary rate. In the laboratory, in high end systems and in the mass market, storage capacity drops in price, and increases in capacity and performance at a ferocious rate.

However, this is not a monolithic phenomenon. There are different sorts of technologies, different sorts of components that develop at different rates. Think of your own desk top PC; ten years ago a PC may well have had a CD-Rom drive, perhaps even a CD writer, and today many machines can write DVDs. There we've seen two generations of technology come to fruition. However, deep inside your PC it's quite possible that you have a Hard Disk Drive three generations or more later than a typical machine from a decade ago.

When you want to store very large amounts of data, and need to do so at a managed cost, this rate of change, and these differences in rates of change are significant.