<b_jonas> slashlearn block device/Block devices are a concession made in Unix to make raw hard disks and magnetic tape have a similar interface to regular files and terminals. Since magnetic tapes can\'t write individual bytes, only entire blocks, the interface isn\'t exactly the same, thus the dreaded dd obs= option was born.

Simple examples:
   calc       - Simple calculator
   classcalc  - Simple calculate defined as a class
   
Complex examples
   ansic       - ANSI C grammar from K&R
   BASIC       - A small BASIC interpreter
   GardenSnake - A simple python-like language
   yply        - Converts Unix yacc files to PLY programs.