RAND and SAGE 1964

The introduction of timesharing on the UT Austin CDC 6600 in 1967, soon after its arrival in 1966, was a student-led initiative that fundamentally changed how the university's computers were used. Instead of originating from faculty or administration, the push for timesharing came from three graduate students, including Forest Baskett, who would eventually run day-to-day aspects of the UTCC systems programming staff. Frustrated by the CDC 6600's primitive batch operating system, the students proposed replacing it with a timesharing system that utilized online terminals. They took their idea to Jim Browne, an early computer science faculty member, who supported the project and got the Computation Center's approval. [1][2]

Baskett drew inspiration from a summer job in 1964 at the System Development Corporation. Spun off from RAND Santa Monica in 1956 to handle the unprecedented software demands of the SAGE project, SDC is widely considered the world's first independent computer software company. The SDC facility originally required an air-conditioning system powerful enough to cool 20,000 homes to offset the heat generated by its early vacuum-tube systems. In this environment, operators monitored radar scopes in dimly lit rooms, surrounded by massive walls of neon bulbs displaying the state of the machine's logic gates. This summer job was while Baskett was an undergrad at Rice University in Houston and already involved with interesting computer research. He was working for a chemistry professor, running simulations of the molecules in a gas and making movies of the results. They had a cathode ray tube with a 16-millimeter film camera attached to it. It could put dots on the screen, take a picture, clear the screen, and advance the film by one click. During this period in the early sixties, Baskett was fortunate enough to experience the SAGE system at SDC.

SAGE, initially designed in the fifties as a military command-and-control system for Soviet bomber defense, featured pioneering real-time processing and early timesharing capabilities. The machine Baskett interacted with specifically was the AN/FSQ-32, commonly referred to as the Q-32, a transistorized prototype that succeeded the massive, vacuum-tube-based machines originally built for the SAGE air-defense network. The Q-32 occupies a unique and somewhat ironic place in computing history. Its cancellation as a military asset is exactly what allowed it to become a pioneering testbed for modern interactive computing.

The Q-32 was originally commissioned by the Air Defense Command to solve the glaring vulnerability of the massive, above-ground AN/FSQ-7 SAGE blockhouses. It was designed to be installed in hardened, underground nuclear bunkers capable of withstanding 200 psi of blast overpressure, called Super Combat Centers. By 1960 the Department of Defense realized that the rapidly increasing yields of Soviet nuclear weapons and the shift toward Intercontinental Ballistic Missiles rendered even these underground bunkers vulnerable. As a result, the Super Combat Center program was cancelled, and the Q-32's military career was terminated before series production could begin, leaving the single completed prototype at the SDC headquarters in Santa Monica.

Because it was no longer needed for active air defense, the Advanced Research Projects Agency, under the guidance of Joseph Licklider, repurposed the Q-32 prototype to research multi-user interactive computing. SDC engineers built the Time-Sharing System for the machine, which achieved its fluid, conversational terminal interactions by utilizing a round-robin scheduling algorithm. The system rapidly swapped active user programs between the machine's 65,000-word core memory and high-speed magnetic drums, allowing it to support upwards of 30 simultaneous users via remote terminals routed through a PDP-1 interface. 

This was the specific architecture that allowed Baskett to sit at a terminal and interact with the machine. It demonstrated that a computer could be an immediate, conversational medium for mathematical exploration. Given the unstructured nature of his summer job, Baskett used the time to teach himself John McCarthy’s Lisp from a textbook and wrote a custom Lisp interpreter directly on the SAGE machine. This hands-on experience became his mental model for how computing should ideally operate when he later encountered the CDC 6600's restrictive, punch-card-based SCOPE batch system. The Q-32's influence extended far beyond Baskett's individual career. In October 1965, the Q-32 in Santa Monica was directly linked via a dedicated dial-up telephone line to the TX-2 computer at MIT's Lincoln Laboratory. This connection marked the first successful transcontinental exchange of data between two independent operating systems, successfully proving the viability of wide-area distributed computing and serving as a direct precursor to the ARPANET. [3]

Understanding this context highlights exactly why Baskett found UT's CDC 6600 so frustrating just a few years later. While the Q-32 at SDC was designed for real-time command, control, and multi-user interaction, the CDC 6600 was engineered purely for maximum scalar floating-point performance. The manufacturer-supplied SCOPE operating system was strictly batch-oriented to keep the central processor constantly fed with scientific simulations. When Baskett and his fellow graduate students proposed building a timesharing system, they were essentially attempting to graft the interactive, user-friendly philosophy he had experienced at SDC onto the raw, unyielding computational power of a machine designed solely to crunch numbers. The students' frustration with the SCOPE system was entirely justified. SCOPE was engineered purely for batch processing, completely isolating the user from the machine. To fix even a minor bug, researchers were forced to submit physical decks of punch cards to operators and wait hours for printed results. The system enforced counterintuitive, rigid rules, such as requiring users to define their maximum runtime in octal seconds, capping execution at exactly 77777 octal seconds, or about nine hours.

When Baskett and his two fellow graduate students approached Jim Browne with their radical idea, Browne's response was enthusiastically pragmatic: "Hmm, that could be fun. Let's try". Browne's backing was the critical catalyst for the project. He had to navigate the university's administrative hierarchy to convince the Computation Center to allow a small group of students to completely replace the core software of a $5.9 million supercomputer. In addition to his work in systems software, Browne served as a Principal Investigator for the Conduit project at UT Austin, working alongside Charles Warlick and George Culp to test, evaluate, and distribute computer-based curriculum materials across different universities. Ultimately, his early experiences supporting timesharing and multi-institutional resource sharing shaped his later career, and Browne went on to become a major proponent of national high-speed computer networks. [2]

Once Browne secured the Computation Center's approval, Baskett and his team ingeniously repurposed the CDC 6600's unique hardware to solve the software bottlenecks. By programming the mainframe's ten independent Peripheral Processors to handle the input/output operations of remote interactive terminals, they freed the central processor to execute user programs in rapid, multiplexed time slices. The trust that Jim Browne and the Computation Center placed in these students yielded extraordinary results. The initial system was up and running within a year and a half, and its subsequent revisions proved so stable that it remained in active production at the university for a remarkable ten years. Browne also went on to serve as Baskett's doctoral thesis advisor, supporting his groundbreaking mathematical proofs on system scheduling and queuing theory that emerged from the project.

The primary goal of the new UT system was to make the computer easier to use, more enjoyable, and highly productive for its target audience of faculty researchers and graduate students. Through data analysis of user habits, Baskett deliberately aimed to optimize the system to minimize customer complaints. The system initially used Teletype terminals and relied on the existing compilers supplied by CDC, ensuring the operating system maintained all the interfaces that users were already accustomed to. Baskett implemented a job-scheduling method using round-robin timeslicing, similar to the one he had experienced on the SDC Q-32, keeping the time slices as small as possible while remaining consistent with system overhead. 

Tasks were kept memory-resident and managed via the 6600's base and bounds registers, which provided memory protection on a per-job basis. Because the CDC 6600 completely lacked hardware paging, segmentation, or virtual memory mapping, user programs were forced to reside in contiguous physical blocks within the central memory. The base and bounds registers provided strict per-job memory protection so users couldn't maliciously or accidentally corrupt each other's data. To effectively multiplex dozens of users with round-robin timeslicing, the system had to swap these memory blocks rapidly. The team achieved this by leveraging Extended Core Storage. When a user's time slice expired, the TAURUS scheduler initiated an extremely fast block transfer, copying the user's entire contiguous address space into ECS and immediately swapping the next active user's program into central memory.

During this period, Baskett encountered Seymour Cray and asked the legendary architect to modify the 6600 hardware so that privileged instructions in user mode would cause an exception rather than a no-op. This was essentially a plea for hardware-level virtualization. Cray’s succinct refusal "No, I don’t think so" illustrated the persistent gap between architectural vision and hardware implementation that Baskett would spend his career bridging. As he assumed leadership of the twenty-five-person systems staff at the computation center, he balanced these practical infrastructure challenges with the theoretical rigor that would define his doctoral dissertation. Between 1971 and 1982, his career exemplified a unique industrial-academic synthesis, bridging the gap between national laboratories and corporate research. He led the Demos operating system for the Cray-1 at Los Alamos National Laboratory, which was notable for its use of software-based property tags, an early precursor to modern object-oriented systems. Simultaneously, he conducted VLSI research at Xerox PARC.

The initial timesharing service, known as RESPOND, was officially initiated on the 6600 in March 1967. It proved to be an astounding success, with the system and its subsequent revisions remaining in production for a decade. RESPOND was later replaced by a more advanced system called TAURUS (Texas Anthropocentric Ubiquitous Responsive User System), which operated as an integral part of the UT-2D dual operating system, managing both the CDC 6600 and 6400. Ultimately, the UT Austin students' project was highly influential in the broader computing industry. It demonstrated the viability of timesharing on the CDC 6600, prompting both Control Data Corporation and the Lawrence Livermore National Laboratory to realize the need for such systems and launch their own competing efforts.

SAGE terminal with interactive radar display and light pen.

SAGE terminal.

SAGE AN/FSQ-7 computer. The Q-32 in Santa Monica was a follow-on transistorized version.

[1] CHM Oral History Interview with Forest Baskett 

[2] Jim Browne 

[3] By June 1963 the Time-Sharing System Model Zero was demonstrated after magnetic drums were added to the time-sharing. Each user was given a priority-based time slice, measured in milliseconds, when the user's program was written from the magnetic drums into much higher speed memory, processed, and then written back to the magnetic drums with any computational changes that had occurred. It was influenced by early experiments at Bolt, Beranek, and Newman, and the CTSS project and Project MAC at MIT. Terminals included several Teletype Model 33 ASRs. In October 1965 Lincoln Labs' used a TX-2 solid-state computer tied to the Q-32 prototype for the first telecommunication of time packets. https://en.wikipedia.org/wiki/AN/FSQ-32#Time-sharing 

CDC 6600 Checkout Testing (Space Wars)

Where there were computers, there were computer games. Even the original CDC 6600 checkout engineers famously used the 6600's innovative CRT monitors for early games like Space Wars, Lunar Lander, and Baseball as a way to test the machine. Because it was among the first commercial computers to feature an interactive cathode-ray tube display console instead of just glowing lights and typewriter text, it became the perfect sandbox for early coders. CDC's checkout and maintenance engineers needed a fast, highly visual way to ensure that all parts of the multi-million dollar system, especially the graphics consoles and peripheral processors, were firing correctly under heavy stress. To do this, they programmed a suite of highly advanced, real-time diagnostic games. [1]

While Spacewar was originally coded on the MIT PDP-1 in 1962, the CDC 6600 Space Wars version took full advantage of the supercomputer's relatively immense processing speed. It featured two vector-graphics spaceships maneuvering in real-time, firing torpedoes at each other while being pulled by the gravity of a central star. Lunar Lander was an early, real-time precursor to the text-based and arcade lander games that would explode in popularity in the seventies. Players had to precisely calculate thrust and fuel consumption using the console controls to safely descend a spacecraft onto a jagged vector-graphics moon landscape without crashing. Baseball was a unique vector-graphic sports game. A pitcher would throw a pitch, and the batter would have to swing with strict timing to hit the ball out into a digitally rendered diamond. Some historical legal documents from Magnavox patent lawsuits in the seventies point to this exact CDC game as a precursor to early video arcade sports games.

CDC engineers openly admitted that the games became the primary incentive for getting the temperamental machines operational. If a newly assembled CDC 6600 could smoothly run Space Wars or Baseball without freezing or crashing, it meant the entire system architecture was completely sound. Because these games utilized the console screens long before commercial video games existed, they can be considered among the first computer games to use graphical displays.

Possibly a checkout engineer?

Baseball [2]

[1] Mention of the checkout testing games https://www.cisl.ucar.edu/ncar-supercomputing-history/cdc6600 

[2] Baseball photo 

[3] One reason that the following link is so interesting is that have met an original european CDC sales rep. He's a prominent art dealer, gallery owner, and respectable old gentleman of Frankfurt. Was there to meet family for their art opening in October 2024. His home was over the gallery, and during the dinner after the event, quite magically we had a conversation about CDC. Just one of those unforgettable things. CDC 6600 arrives at CERN in 1965 

CDC at UT Austin and IBM at Exxon Houston

There's a curious parallel between UT Austin's CDC hardware and Exxon Houston's IBM hardware during the sixties and seventies, bookended by a shared IBM era in the fifties and a shared Cray era in the eighties. CDC and Cray were members of a family of Minnesota companies (ERA, CDC, Cray) that, along with its UNIVAC relatives, was a vigorous competitor to IBM in the engineering, scientific, national lab, and cryptography fields. In a sense, UT Austin moved from IBM to the ERA tradition in the sixties, and Exxon Houston followed in the eighties. UT Austin's early move was due to David Young's being firmly in the ERA tradition from his work at Ramo-Wooldridge (TRW) in the fifties. He arrived at UT in 1958 and led the acquisition of the CDC 1604 in 1960 and CDC 6600 in 1966. The CDC Cyber hardware that UT acquired in the seventies was essentially updated versions of the CDC 6600, based on the same 60-bit architecture and running similar code.

There were multiple important connections between computing at UT Austin, Exxon, Rice, and Houston. A sign of these connections was the story of how, in 1958, Humble Oil in Houston (now Exxon) donated its IBM Card-Programmed Electronic Calculator to UT Austin. UT’s Al Matsen was a consultant for Exxon Houston and New Jersey for over thirty-five years. The CPC was a landmark gift and a direct result of Matsen’s extensive ties. To bypass bureaucratic paperwork, Matsen, his graduate students, and other faculty physically carried the heavy machine components into Welch and installed it themselves. Exxon had acquired the CPC in 1952 and used it to implement ground-breaking subsurface reservoir simulations and the beginnings of the ADI Alternating Direction Implicit techniques for Finite Difference Methods. This work put Exxon, Rice University, and Houston in a leading position for subsurface modeling and computational engineering and science.

ADI was forged in late 1953 out of urgent commercial necessity by Peaceman, Rachford, and Douglas. Driven by the pragmatic need to simulate oil reservoirs for high-stakes drilling decisions, they bypassed academic idealism in favor of industrial utility. Rather than chasing elegant theorems, they engineered ADI as a brilliant, gritty algorithmic hack, splitting complex multi-dimensional problems into a sequence of cheap, one-dimensional coordinate sweeps to circumvent both the memory bottlenecks of early hardware and the finicky tuning required by SOR. The alignment of Exxon with IBM, and David Young’s association with UNIVAC and Control Data Corporation, mirrors the structural, financial, and philosophical divides of the early computing era. [1]

The IBM CPC was not a computer in the modern sense. It was a hybrid electro-mechanical system. It consisted of an IBM 402 or 417 Accounting Machine (the printer/controller) connected to an IBM 604 Electronic Calculating Punch (the arithmetic unit) and an electromechanical storage unit. It functioned as a decentralized network of specialized units rather than a unified stored-program architecture and was fundamentally incapable of holding both the data and the instructions required for the Simplex Method. Consequently, the program existed not as a digital state within the machine, but as a physical sequence of punched cards. This required the operator to function as a manual control unit, physically re-entering card decks to execute the iterative loops essential for finding an optimal solution within a linear system. 

The development of the CPC itself actually originated from clandestine, user-driven engineering at Northrop Aircraft rather than inside IBM's own research labs. In late 1946, a specialized computing group at Northrop led by engineers Greg Toben, Bill Woodbury, and Rex Rice was tackling complex aerospace calculations, such as jet propulsion and guided missile trajectories, which vastly outstripped the capacity of standard accounting machines.

Because true stored-program computers were not yet available, the Northrop team decided to build their own hardware solver by merging two leased IBM machines: the new IBM 603 Electronic Multiplier, which was fast but lacked sequencing control, and the older IBM 405 Accounting Machine, which was slow at math but had excellent card-reading and printing capabilities. In direct violation of their IBM rental agreements, the Northrop engineers took the protective covers off the machines, exposed their internal wiring, and physically linked the two units together. They affectionately dubbed their makeshift, hybrid creation the poor man's ENIAC.

This prototype, which the engineers nicknamed Betsy, was remarkably powerful but suffered from physical instabilities. The multiplier section would occasionally freeze mid-operation, trapping card decks inside. To clear the jam, the operators often resorted to physical force. In one famous incident, an engineer was told to "Kick it, Gib", and his literal kick drove a heavy metal cover directly into a 60-ampere fuse block, causing a massive, hazardous shower of sparks. When Northrop's founder, Jack Northrop, reached out to IBM's CEO Thomas Watson to demand manufacturing support and standard parts for their modified system, IBM realized the commercial potential of the hybrid concept. IBM immediately flew Woodbury and his colleague George Fenn to New York to present their 603 and 405 combo. IBM's engineers then standardized the physical interfaces, replaced the 603 with the newer 604 calculating punch, and officially announced the commercial Card-Programmed Electronic Calculator in May 1949.

Even after the commercial release, Northrop continued to drive the CPC's evolution. Early users struggled because instruction cards had to point to highly specific, hardwired microprograms on a physical plugboard, making it almost impossible to share programs. To break this hardware bottleneck, Northrop's Rex Rice engineered a general-purpose control panel. By wiring a generalized set of logical pathways and math routing systems directly into the board, programmers could write various mathematical applications entirely on standard card decks without needing to manually rewire the plugboard for every new problem.

The CPC can even be traced a few years further back, to 1943 Los Alamos and the race to build the atomic bomb. All of the pieces that would become the CPC three years later were already being brought together at Los Alamos and even earlier at Columbia University, and it’s extremely likely that some of the Northrop researchers had been present at Los Alamos and possibly Columbia. Here's a description of the arrival at Los Alamos of the pieces of what soon would become known as the CPC, and Richard Feynman’s reaction.

Feynman, frustrated, turned to Nicholas Metropolis, a mustached Greek mathematician who later became an authority on computation and numerical methods, and said, “Let’s learn about these damned things and not have to send them to Burbank.” (Feynman grew a temporary mustache, too.) They spent hours taking apart new and old machines for comparative diagnosis; learned where the jams and slippages began; and hung out a shingle advertising, “Computers Repaired.” Bethe was not amused at this waste of his theoreticians’ time. He finally ordered a halt to the tinkering. Feynman complied, knowing that within weeks the shortage of machines would change Bethe’s mind. Escalation of the computation effort came in the fall of 1943 with an order to IBM for business machines to be delivered to an unknown location: three 601 multipliers, one 402 tabulator, one reproducer-summary punch, one verifier, one keypunch, one sorter, and one collator. Astronomers at Columbia had been experimenting with punch-card computing before the war. A multiplier, an appliance the size of a restaurant stove, could process calculations in large batches. Electrical probes found the holes in the cards, and operations could be configured by plugging groups of wires into a patchboard. Among the computation-minded at Los Alamos, the prospect of such machines caused excitement. Even before they arrived, one of the theorists, Stanley Frankel, set about devising improvements: for example, tripling the output by rearranging the plugs so that three sets of three- or four-digit numbers could be multiplied in a single pass. Having requisitioned the machines, the scientists now also requisitioned a maintenance man—an IBM employee who had been drafted into the army. They were gaining adroitness at military procurement. The crates arrived two days before the repairman; in those two days Feynman and his colleagues managed to get the machines unpacked and assembled, after a fashion, with the help of nothing but a set of wiring blueprints. [6] 

Exxon donated its IBM CPC to UT in 1958. The CDC Cyber was essentially an updated CDC 6600. By the eighties, both UT and Exxon were in the ERA tradition with Cray hardware.

Is this Seymour Cray during installation of the CDC 6600 in 1966? Genuine question, as it does seem at least possible.

Official event for the CDC 6600 in 1966. David Young is at the very top center, somewhat less visible because of lack of contrast against the background. Curiously, Al Matsen seems not to be present in this photo. Both Young and Matsen are variously described as founders and heads of the UT Computation Center.

[1] SOR Successive Over-Relaxation and the work of David Young at TRW were prominently applied to fluid and heat flows for atmospheric reentry vehicles. At the same time, ADI Alternate Direction Implicit was being applied to fluid and heat flows for the oil industry in Houston. This was all in the mid and late fifties, and among the most important early applications of computers in modeling and simulation, alongside Dantzig's work on Simplex at RAND.

[2] For more about Exxon Houston, A Personal Retrospection of Reservoir Simulation, Donald Peaceman 

[3] The photos above related to the CDC 6600 are thanks to the Briscoe Center 

[4] Here's an excellent new post about the IBM CPC from Ken Shirriff.

[5] Notes about the post 6600 CDC hardware in Austin. UTCC upgraded to systems like the Cyber 170/750 and 175, which maintained compatibility with the older 6000 series code but introduced crucial magnetic-core and semiconductor memory enhancements to support operational runs on much larger scales. The Cyber 170/750 was a critical high-performance resource managed by the UT Computation Center. While the university's primary, general-access academic mainframes such as the original CDC 6600 and early Cyber systems were famously housed in an underground facility beneath the East Mall on the main campus, the Cyber 170/750 was deployed differently. The university utilized facilities at the Balcones Research Center, now known as the Pickle Research Campus, to host high-performance systems like the Cyber 170/750. At this off-campus site, the 170/750 was dedicated to handling specialized research and mathematically intensive data analysis tasks. Researchers also utilized a CDC Cyber 175 during the late seventies and eighties. At the time, the Cyber 175 was one of Control Data Corporation’s top-tier, high-speed scalar processors, and it was used intensively for complex finite element and alternating-direction method simulations to solve the types of convection-diffusion problems that frequently appear in reservoir engineering and geology.

[6] James Gleick, Genius: The Life and Science of Richard Feynman (New York: Pantheon Books, 1992)