Honeywell 6000, L66 & L68 (Large-Scale Honeywell Systems)    Medium-Scale Honeywell Systems Multics MIT
After working on the Medium-Scale systems, I was promoted to the big iron.  Pictured here is the Honeywell 6180 at MIT IPC (Information Processing Center), circa 1976, skin doors open to show off the blinking lights.  MIT ran the machine with doors open so the operators could see the AQ (accumulator/quotient) register display, which gave them an idea of system activity.

We had a Dual Processor L68 at CSC in Moorestown, NJ which was the SDF (Software Development Facility) for U.S. Naval War College.  It was used as a development machine for ENWGS (Enhanced Naval Warfare Gaming System), the U. S. Navy's official war gaming system that provided multiplatform, multiwarfare, multisite, real-time war gaming and training.  I learned that some customers actually left the doors open to impress visitors to their facility.

These Large-Scale systems were designed to run either GCOS (General Comprehensive Operating System) or Multics (Multiplexed Information and Computing Service.) 

GCOS is a multithreading, multiprogramming operating system originally oriented towards batch processing, but was enhanced to support timesharing and online transaction processing environments. Systems running GCOS today use it mainly for batch and OLTP (Online transaction processing) or as a backend enterprise server.  Hardware and software features combine to render the operating system unusually secure for an operating system of its generation and class.  Side note: GCOS also was known as Gods Chosen Operating System by its users. Multics B2 Certification
was started in 1964 as a cooperative project led by MIT along with General Electric and Bell Labs.  It was the first OS to use a hierarchical file system, and one of the first operating systems to use the now-standard practice of per-process stacks in the kernel. Multics was also one of the first computer systems written in a high-level programming language (PL/I), and possibly the first such system to emphasize built-in computer security.  In 1985, Multics was issued certification as a B2 level secure operating system using the Trusted Computer System Evaluation Criteria from the National Computer Security Center (NCSC) a division of the NSA, the first operating system evaluated to this level. Fans of Multics also note its role in the subsequent development of UNIX and Linux.  Also, Multics heavily influenced the design of GCOS 64 & GCOS 7, which ran on the Medium-Scale L64, DPS7 and DPS7000.

Initially, Multics was built with tools provided by MIT's compatible time-sharing system (CTSS), an early time-sharing OS with a robust file system. The first version of Multics was developed for the GE-645, a 36-bit mainframe computer that included multiple security levels and instructions for handling virtual memory. By modifying the addressing scheme to use 18-bit segments (files) and 18-bit addresses, the computer's designers dramatically increased its theoretical addressable memory size. By using small subroutines called operators for short but standard code-sequences, the Multics compiler optimized code density and preserved the system's main memory. Dynamic linking, another Multics innovation, enabled applications to use the latest version of any called routine.

A Virtual Memory Operating System

Although these Multics features were important, the memory savings provided by sharing code between processes created had a huge impact. Virtual memory enabled programs could address a space far larger than physical memory. Therefore, Multics machines handled larger and more complex applications than other computer systems, but applications that used virtual memory did not perform as well as applications that were 100% memory resident.

General Electric sold its entire computer business to Honeywell in 1970. A year earlier, Bell Labs had also ended its involvement with Multics, which freed up resources for the development of its new UNIX operating system several years later. Only 84 Multics sites were ever installed world-wide, each representing multi-million dollars expenditure and serving hundreds of users. The system was used by education, automobile & aircraft manufacturers and military installations.

Note: Some of this information was derived from Multics Stories (Tom Van Vleck), blogs and Wikipedia. MIT 6180 Photo by THVV.

DPS8000 DPS8000
Pictured here is a DPS8000 Model 82 which was the last model generation that I ever installed and worked on before leaving the mainframe world.  This particular machine is a Dual Processor, where the one I installed was a Triple Processor, which had another four 2' wide cabinets to form a T configuration.  A Fourth Processor could be added making the cabinet configuration a plus sign that would occupy 14' x 14' area of computer room floor, which was much smaller than its predecessors.  A maxed out configuration could have 256 MB of main memory.  These systems ran the GCOS 8 operating system.

Across the medium and large systems, we shared a lot of the peripheral devices.  On the large 
systems, we even used the IBM 3380 disks and it wasn't uncommon to have 32, 64 and even 128 or more of disk drives connected to the mainframe in large systems such as we had at GE Aerospace, St of NJ and Colonial Penn Insurance Company.  In those large installations, you would find massive rooms dedicated to rows and rows of disk drives.

Disk storage space was quite expensive back then.  Below is a comparison of the costs in 1980 for 20GB of 3380 disks with an estimated value of from $648,000 to $1,137,600 versus the costs in 2010 for 32GB of SD Memory with an estimated value between $100 and $150.  Also, there is a big difference in costs to operate & cool as well as the floor space required. IBM 3380 MicroSD