# The Five-Minute Rule 10 Years Later, and Other Computer Storage Rules of Thumb - Microsoft, 1997

• [Paper] [Mirror]

• While “all aspects of storage performance are improving,” they are doing so at different rates.
• They talk about the difference between
• the technology ratio
• PagesPerMBofRAM / AccessesPerSecondPerDisc
• and the economic ratio
• PriceOfDisc / PriceOfMBofRam
• The Five Byte Rule is now The One Byte rule
• Mainframe processors are expensive and thus follow a 10 byte rule
• They discuss a rule for sequential access common in sorts and joins
• With their assumed numbers they determine one-minute break even point where it makes sense to cache disc data on main memory if it will be needed within a minute
• RAID
• RAID 1 decreases cost of reads a little bit but doubles cost of writes
• RAID 5 increases the cost of writes by a factor of 4
• Tape
• They give numbers for tape versus RAM and tape versus disc
• They discuss when buffer managers should checkpoint their state
• They also talk about how having hot standbys can change the economics