Hi Bijoy,

I wish to run NEMO3.6 using XIOS1.0 in the detached mode. For this configuration do I need to define the %XIOS_HOME in 'arch' file to the installation directories of XIOS.

The definition of %XIOS_HOME variable is not related to a particular mode, it is just an alias that can be used when linking the header files and libraries of XIOS with %XIOS_INC and %XIOS_LIB.
In fact FCM uses only %USER_INC and %USER_LIB for the compilation phase.

Also, may I please know the meaning of following command (from NEMO_BOOK) used for running XIOS in detached mode.

mpirun -np 62 ./nemo.exe : -np 2 ./xios server.exe

Does it mean both nemo and xios will run in parallel (similar to a coupled model) or xios run will takes place after the nemo run completion.

NEMO and XIOS always runs in parallel, the difference with detached mode (XIOS server) is that you can assign dedicated processors only for the XIOS operations. It quickly becomes essential to use this mode in order to speed up the run of configurations with a lot of IOs.
The example from the NEMO ref. manual allocates 62 procs for NEMO and 2 procs for XIOS, so it requires to have 64 procs available. The best setup for a given configuration have to be determined with testing.

Regards,
Nicolas