 When address spaces increased from 16 to 32 bits, kernel design was no longer constrained by the hardware architecture, and kernels began to grow larger.The Berkeley Software Distribution (BSD) of Unix began the era of larger kernels.In addition to operating a basic system consisting of the CPU, disks and printers, BSD added a complete TCP/IP networking system and a number of "virtual" devices that allowed the existing programs to work 'invisibly' over the network.