Unix System brief structure

1.Hardware

2.Kernel

3.Programs

We'd better view the system as a set of layers.

The Hardware offer the basic services to Unix,and the Kernel insulating them. Programs interact with the Kernel by invoking SYSTEM CALLS.

Basic Programs include:sh,who,date,wc,grep,ed,vi,ld,as,comp,cpp,nroff,a.out..etc.The more advanced Programs in outer layers include:c compiler..etc.