Originally posted by: SystemAdmin
> I just read this paper -
>
http://www-1.ibm.com/servers/aix/whitepapers/db_perf_aix.pdf, > little confusion with the concurrent IO and generally asynchronized IO.
> What is the difference between? or they talked the same thing?
The two are not the same, but they are related.
In computer science, concurrency is the shared property of two entities
whose extent overlap.
In computer science, synchronicity is the property of an operation whose
extent is dependent on some other process, asynchronicity is the assumed
or actual absence of synchronicity.
The extent (time that they exist) of processes like reading have a definite
and distinct start and end.
If reading, starts before write ends, or vice-versa, then reading and writing
overlap in time, and are thus concurrent.
If reading cannot begin before writing ends, and writing cannot begin before
reading ends, then reading and writing are not concurrent.
If the reading start and end times are set by a separate clock signal (e.g.
ps/2 protocol), the reading is synchronous with the clock signal.
if the start and end could occur at any time (e.g. eia232 protocol), the
reading is asynchronous.
By definition,
a synchronous process is concurrent with the process it depends on.
Ethernet over coax is normally asynchronous (any node may start and end
transmissions at any time), sending is not concurrent (a second node
cannot start sending until all other nodes end sending),
but receiving is concurrent with sending (the receiving node begins receiving
before the sending node ends sending).
Hopefully helpful,
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