Synchronous and Asynchronous

[jayvrabara]

Synchronous and asynchronous are two big words that seem intimidating
but are quite simple. Synchronous simply means that all events are
occurring in a certain time order that can be predicted. A certain
event would always follow another and they can’t be interchanged.
Asynchronous is the opposite of synchronous. In asynchronous
processes, there is no time order. Certain events can, and often do,
interchange. An excellent synchronous example is music. Each
participating instrument needs to be in rhythm with the others or else
the music won’t sound right. For asynchronous, a good example would be
traffic. Vehicles move at different rates of speed and it is common
for one to move past another. In most applications, synchronous
operation is essential as having an asynchronous operation would
literally mean chaos. Examples of this are railways and airports. In
these scenarios, it is important to know which vehicle goes first in
order to avoid collisions. The order of things are carefully planned
to facilitate a smooth flow and changes to the plan are few and far in
between. Although synchronous operation is often preferred, there are
certain cases where it is not needed. There are even cases where
synchronous operation can be detrimental to the objective. An example
where synchronous operation is not really necessary is in internet
browsing. Prior to AJAX (Asynchronous Javascript and XML) most
webpages need to be reloaded in its entirety to change the information
on a small section. With AJAX, it is now possible to update that
certain section while leaving the rest of the page untouched. This is
beneficial as a smaller amount of data needs to be transmitted and the
user doesn’t have to endure through the whole page refreshing. AJAX is
asynchronous because page updates are no longer synchronized. In
computer operations, I/O is an area where synchronous operation
becomes detrimental. Synchronous operation in this regard mean that
the processor needs to wait for the data to be written or read before
it can continue. The problem is, I/O devices like hard drives and
especially floppy drives, which have mechanical parts, are very slow.
If the processor needs to wait for the drive to finish, it would be
wasting a lot of time. Asynchronous operation allows the processor to
do other things while waiting for the read/write to finish and just
carry on once the operation has succeeded.


Summary:
Synchronous means in time order while Asynchronous means no time order
Synchronous is preferred over asynchronous in many real world
applications Synchronous can perform worse in certain scenarios than
asynchronous