•E.g. An aligner can process X reads per second on
a single CPU at a data rate of Y bytes/sec
–~200 million reads in 10 hours
–Each read 50 bases at 10 bytes per base
–2.7 MB/sec
•Design 100TB storage and connect it to a CPU
resource
•Design bandwidth to be 10 Mb/sec – plenty of spare
bandwidth
•Now we want to complete the job in an hour and get
permission to buy 10 more CPUs – great!
BUT
For the 10 CPUs to run at maximum
speed, they need to be supplied data at 27MB/sec
Our bandwidth is 10MB/sec
Therefore, no matter how many CPUs
we buy, the job will never run faster than ~ 2.5 hours .
How about optic fibers?