How to check memory size ?? How to get total memory size ?

Solaris
dmesg | grep mem
prtdiag | grep Memory
prtconf -v | grep Memory

AIX
bootinfo -r
lsattr -E1 sys0 -a realmem
getconf REAL_MEMORY

HPUX
dmesg | grep Physical
/opt/ignite/bin/print_manifest | grep Memory
machinfo | grep Memory

Linux
dmesg | grep Memory
grep -i memtotal /proc/meminfo
free