BAD HARDWARE WEEK

In 1987, Jim Gray and Gianfranco Putzolu published their now-famous five-minute rule for trading off memory and I/O capacity. Based on then-current prices and performance characteristics of Tandem equipment, Gray and Putzolu found the price of RAM to hold a 1KB record was about equal to the (fractional) price of a disk drive required to access such a record every 400 seconds.

Now? Seems we will get soon a new level in storage hierarchy for a 5 minutes rule: Flash storage.
The 20-year-old five-minute rule for RAM and disks still holds, but for ever-larger disk pages. Moreover, it should be augmented by two new five-minute rules: one for small pages moving between RAM and flash memory and one for large pages moving between flash memory and traditional disks.