Oracle Instance Concepts - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 104

server process or shared server process. In dedicated server
process we have one server process per session whereas we in a
shared server process we have multiple sessions served by one
server process. We will learn in detail regarding it later in this
book. Stack space in the PGA is utilized by server process to
hold variables, arrays and other useful information pertaining to
connected session. Unlike SGA, which is shared by several
background processes, PGA is an area for the server process
utilization and utilized for sort operations, containing
information pertaining to session and stack space for variables
and arrays.
Oracle Server can be configured to run under Shared Server
mode or as Dedicated Server mode. The Figure 4-7 shows
Oracle Instance working under Shared Server configuration. The
beauty of shared server configuration is that a single server
process handles multiple sessions and hence the idle time of
server process reduces.
Figure 4-7: Background processes of Oracle Instance. Oracle Instance
running under Shared Server Mode is shown. RECO, LGWR, SMON,
PMON, ARCn etc. are all background processes. SGA is the shared
part of memory architecture of Oracle. Oracle can be configured to run
as dedicated server mode or shared server mode.