2) Text file editor

We expected most of our users to write programs for compilers and assemblers. These programs would be written as text files, then fed to the appropriate compiler or assembler. Thus we needed facilities for conveniently writing and modifying text files. We did not want to build these text editing facilities into the system. Rather, we intended to write a text editor as a user program for the system. The amount of data that must be immediately available to the text editor should be fairly small, a couple of small text buffers and sufficient information to tell where to write the text in an output text buffer, and where to get new text from an input buffer. These buffers should need no more than a few hundred words, and the additional words should also be at most a few hundred. All in all, the total should be less than a thousand words. On the other hand, it was expected that the program implementing the editor would be considerably larger than this, hence there must be some way to share that program among several users. That is, there should be only one copy of the code for the editor in the main store (ECS) at one time, even though several persons were using it.