At 08:03 PM 1/15/99 +1, you wrote: The first commercially available IBM disk system was the IBM 305 RAMAC, but I believe the disk was just a peripheral device like a tape drive, not a system disk like we view it today. There certainly was no operating system stored on the disk and I doubt they even stored a program on the disk. It was pretty small electronically although it was physically huge, and incredibly slow because it only had one read/write head that had to be moved Since all IBM computers of the era, the 700's and 7000's were punch card fed machines, the programs were stored on punched cards and loaded each time they were to be run. Tape drives held intermediate results and input and output data, but not programs. At some point the the 7000 series life I believe there was a primitive "Tape Operating System", or TOS, developed so that once a program was debugged, the compiled binary version could be stored on tape, and a punch card "IPL" program could read that tape, load the program and then the machine would continue on just as if it had read the program from punched cards. After the 305 RAMAC was designed, a disk drive that I believe was called the 2305 was developed and it was hooked to the 7000 series machines. At some time around 1964 IBM coupled a 2305 to a 7044 which had a Direct Couple interface to a 7094 and used the 7044 to stage and control program loading on the 7094. A primitive "DOS" was developed called IBSYS, but all it did was que programs and data on the disk to be run on the 7094, one program at a time. This greatly minimized operator setup time and kept the very expensive 7094 humming. I don't think it was until the delivery of the S/360, in the 1968 time frame, that IBM had an operating system that they called DOS, but maybe there is an IBM expert in the group that could comment. -- db =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Dean Billing Phone: 530-752-5956 UC Davis FAX: 530-752-6363 IT-CR EMAIL: drbilling(a)ucdavis.edu One Shields Way Davis, CA 95616