Layers

The major factor which contributed to our allocation of responsibilities within the layers was a desire to produce an interim system as soon as possible. We wanted a system which we could use to support further development, i.e., provide editing and storage facilities for the programs we were writing. Also, we felt that such a system would demonstrate to the administration that we could eventually construct a final working system. (In fact, we did demonstrate a two teletype system at the end of the first year and moved our program development under the system six months later.) To this end, all facilities which we felt were unnecessary for an interim system were pushed to higher layers. The first layer would support the interactive programs that reside in ECS. We called this the ECS system. All data storage would reside in ECS, while access to the disk would be provided similar to that for any other I-O device. It was intended that the addition of a temporary executive would produce our interim system. This temporary executive (called the Bead) would ignore all protection problems. The second layer would introduce disk files and directories. It would convert the real disk into a collection of virtual disk files. We called it the disk/directory system. It would also provide disk swapping of non-interactive programs. The third layer was to be the executive. This executive was to provide password protection for identification of users, charge accounting and convenient commands for starting programs.