Smalltalk, the Dynabook's programming tool, was originally envisioned as a simple language suitable for use by children without any prior knowledge of computers. The choice of name reflects this intention. The very first Smalltalk system was a thousand lines Basic program, which successfully computed 3+4 in October 1972. It was followed by an assembly code implementation which became known as the Smalltalk-72 system two months later. D. Ingalls was the chief implementor of these systems. In 1974. Smalltalk was ported to the Alto computer and a number of experiments in building graphical user interfaces were performed. Applications included turtle graphics, a mouse-driven program editor, a structured graphics editor, an animation system and a music system. Smalltalk-72 also served as a base for experimental programs in teaching object-oriented programming to high-school children . Smalltalk-74 added better facilities for bit-mapped graphics (class BitBlt) and virtual memory. This improved system was used to implement an information retrieval system and a window-based user interface. Smalltalk-74 evolved into Smalltalk-76, which was based on a much cleaner design. Smalltalk-76 also added the idea of inheritance, which had been absent from the two earlier systems. The concept of "byte codes" as a base for portable implementations was proposed and a micro-coded emulator for this design resulted in much improved performance. Smalltalk-76 was used on a daily basis by more than 20 people for a period of 4 years. A further clean-up of the implementation (Smalltalk-78) then led to Smalltalk-80, the first system which was made available outside Xerox Parc.