Check Rasperry Pi Hardware Version

$ cat /proc/cpuinfo
...
Hardware : BCM2835
Revision : b03111
Serial : 100000005290e8ae
Model : Raspberry Pi 4 Model B Rev 1.1

$ cat /proc/cpuinfo
...
Hardware : BCM2835
Revision : a22082
Serial : 00000000d8eb7d7f
Model : Raspberry Pi 3 Model B Rev 1.2

Overview of Raspberry Hardware can be found at RPi HardwareHistory