Availability Chart
Paul Green
March 11, 1986

The following chart relates the level of availabilty to downtime per
year.  For example, "4 nines" of availability is 52 minutes and 33
seconds of downtime per year.

     NINES     AVAILABILITY   PER CENT       DOWNTIME / YEAR
     -----     ------------   --------       ---------------

     1         .9             90%            36 DAYS, 12 HOURS

     2         .99            99%            3 DAYS, 15 HOURS, 36 MINUTES

     3         .999           99.9%          8 HOURS, 45 MINUTES

     4         .9999          99.99%         52 MINUTES, 33 SECONDS

     5         .99999         99.999%        5 MINUTES, 15 SECONDS

     6         .999999        99.9999%       31.5 SECONDS

     7         .9999999       99.99999%      3.15 SECONDS

     8         .99999999      99.999999%     315 MILLISECONDS

     9         .999999999     99.9999999%    31.5 MILLISECONDS

(end)