When they started to build the Linux kernel, they had a few great reference implementations of UNIX to base their design on: BSD and SysV UNIX. Both were avail

When they started to build the Linux kernel, they had a few great reference implementations of UNIX to base their design on: BSD and SysV UNIX. Both were available as source, and both had technical books describing their system architecture. Linux has even been criticized for being a fairly conservative reimplementation of traditional UNIX.