I/O - the orphan of computer architecture
Traditionally, the CPU time is considered the most adequate
measurement of performance.
But CPU time, by definition, ignores I/O, so it does not show the real
response time, about which the customer cares first of all.
By Amdahl’s law, if we only improve the CPU performance, soon
every task will become I/O bound.
In some cases, I/O (response time) is not so important because there
is always another process to run while waiting for I/O.
In other cases, I/O performance is crucial. E.g.:
--- Bank transaction management
(imagine waiting at an ATM for 20 min!)
(the only waiting “process” is the user)