raspi-commands    (http://www.makeuseof.com/tag/15-useful-commands-every-raspberry-pi-user-should-know/)
==============

sudo raspi-config

cat /proc/cpuinfo
cat /proc/meminfo    displays details about the Raspberry Pi’s memory
cat /proc/partitions reveals the size and number of partitions on your SD card or HDD
cat /proc/version    shows you which version of the Pi you are using.

free -o -h           to see how much free system memory is available, while 

vcgencmd measure_temp
vcgencmd get_mem arm && vcgencmd get_mem gpu     will reveal the memory split between the CPU and GPU