Difference between instance and application server

On appl. server(instance) you may have
and SPO, UPD, ....all kind of processes - only one message server can be
run - this show witch is central instance(server).
About DB instance - db can be run on
separate server(machine). in this case db instance will not be on Central
SAP instance

Hi Hristo,

The terms `application server` and `application
instance` are synonymous with R/3 instance. An
instance defined with the message and enqueue service
can be referred to as the `central instance`.

Central Instance-where all the message, dialog and database instances
are running.
Application Server - is where only dialog instance is running

the difference is that message server
is running only on central instance(must be one process for the system).

BUT................... there is some
cases in witch you will need to have more that one message server(very
rearly)..
That is.

Hi,
App Server is nothng but a message server.
Its going to act as a middle ware taking request and giving the response back.