Special system processes (non user processes)

There were three kinds of special processes. The first kind handled the interpretation of responses from the ECS system disk I-O code. These responses were sent by the ECS system to a single event channel. (We did not want the ECS system to have to know about the many user disk processes.) In order to send a response to the process originating the request, an intermediate process examined the response to determine appropriate further processing. If necessary, an event would then be sent on an event channel looked at by the originating process. A second kind of special process initiated disk I-O for such functions as closing files. File closing was a two step procedure in which all blocks except the header were first written to the disk. When these writes had been successfully completed the header was written. Since the modified pointer and data blocks were written at new locations on the disk, the effective disk version of the file showed no change until the header itself was written. Thus the disk representation of the file was always a good disk file. This procedure took time, and it was desirable to permit the user process to proceed with other business. Hence a special process performed the step by step procedure. The third kind of special disk system process controlled the total disk space allocated to particular user directories. The information about space held by these directories was all held in one disk file, and maintained by this special process. This process had in itself a disk system which treated the special file just as any other disk file. For historical reasons this process was a part of the disk level and accepted commands from the directory level.