The 7 Levels of Operating System

The 7 Levels of Operating System

From Wartime Codebreaking to Global Cloud: The Military Imperatives That Built Modern Computing

BLUF (Bottom Line Up Front): Modern operating systems evolved through seven distinct stages over seven decades, but this progression was fundamentally shaped by three World War II military imperatives—cryptanalysis, ballistics calculations, and nuclear weapons development—that remain absent from popular histories. The classified nature of Britain's Colossus codebreaking computers until 1975 distorted computing's origin story for three decades, crediting America's ENIAC as "first" when Colossus predated it by two years. Parallel evolution of real-time military systems like the Navy's NTDS, which evolved into Aegis and Cooperative Engagement Capability, created a distinct trajectory optimized for guaranteed response times rather than general-purpose computing, yet these systems powered the defense infrastructure upon which modern network-centric warfare depends.

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The Hidden Origins: Cryptanalysis Drives Electronic Computing

Cryptanalysis represents the single most important driving application in early computing history, yet it remained classified for decades. Colossus, the first large-scale electronic computer, went into operation in 1944 at Britain's wartime code-breaking headquarters at Bletchley Park. Tommy Flowers spent eleven months designing and building Colossus at the Post Office Research Station, Dollis Hill, with the first machine delivered to Bletchley Park in late December 1943/January 1944 and working in early February 1944.

Colossus predated America's ENIAC by two years, making it arguably the world's first programmable electronic digital computer. The machine was built to carry out fundamental stages of the Tunny code-breaking process at electronic speed, cracking encrypted German military transmissions that contained top-level messages from Hitler and his army high command in Berlin. By war's end, 63 million characters of high-grade German communications had been decrypted by 550 people helped by ten Colossus computers. Experts have suggested that the Bletchley Park code breakers may have shortened the war by as much as two years.

Yet Winston Churchill ordered Bletchley Park machines destroyed after the war and kept operations secret under strict injunction that was not lifted even after the war ended. Not until 1975 when the first information about Colossus was declassified could the story begin to be told. This three-decade secrecy meant ENIAC received credit as computing's origin, fundamentally distorting the historical narrative.

273 women recruited during World War II to operate Bletchley Park's Colossus machines entered programming using switches and telephone-exchange plugs in a process called "pegging a wheel pattern". The cryptographers determined which patterns to run while the "Wrens" (Women's Royal Naval Service) operated the machines—yet their contributions didn't emerge publicly until decades later.

Ballistics and Nuclear Calculations: Parallel Military Imperatives

ENIAC was designed by John Mauchly and J. Presper Eckert to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory at Aberdeen Proving Ground, Maryland. Groups of women nicknamed "computors" struggled to keep up with demand for artillery firing tables requiring calculation of wind speed, humidity, temperature, muzzle velocity, air density, and elevation. A skilled person with a desk calculator could compute a 60-second trajectory in about 20 hours, while the Bush differential analyzer produced the same result in 15 minutes, but ENIAC required only 30 seconds.

Computing also proved essential for nuclear weapons calculations at Los Alamos and for NASA Langley's orbital trajectory planning during the space race. These three parallel wartime efforts—cryptanalysis at Bletchley Park, ballistics at Aberdeen, and nuclear calculations at Los Alamos—established computing as essential to modern warfare and national security, driving development far more powerfully than commercial applications during computing's critical formative years.

Batch Processing: The University Experience

The evolution from these specialized wartime machines to general-purpose computing proceeded through batch processing systems. At University of Maryland in 1965, students carried punch card decks containing Fortran programs and Job Control Language (JCL) commands to IBM System/360 installations, then returned 24 hours later for printed output. This tedious process—where a single misplaced card could ruin an entire program—represented the standard computing model for a generation of programmers.

IBM's OS/360, introduced in 1966, became one of the world's first major operating systems, incorporating virtual memory management and Job Control Language to specify job requirements and dependencies. Batch processing originated when monitors were developed to process a series of programs from magnetic tape prepared offline, with examples including IBM's Fortran Monitor System and IBSYS for IBM's 709x systems in 1960.

Time-Sharing: Democratizing the Mainframe

The Compatible Time-Sharing System, developed at MIT in 1961, pioneered interactive computing and laid groundwork for future user-centric operating systems. The Dartmouth Time-Sharing System, developed between 1963 and 1964, became the first successful large-scale time-sharing system and the platform for which BASIC language was developed. Professors John Kemeny and Thomas Kurtz learned about time-sharing from colleague John McCarthy at MIT, who suggested "why don't you guys do timesharing".

IBM's Time Sharing Option (TSO), deployed at companies like Hughes Aircraft, provided interactive programming environments for professional developers, offering editors, debuggers, and the ability to submit batch jobs and view results without waiting for printed reports.

Unix: The Foundation of Modern Systems

Multics, designed as a time-sharing system beginning in 1964 by MIT's Project MAC, Bell Labs, and General Electric, introduced hierarchical file systems and per-process stacks in the kernel. When Bell Labs withdrew from the project in 1969, personnel including Ken Thompson and Dennis Ritchie subsequently created Unix.

Unix development began in 1969 when Ken Thompson wrote the system for a PDP-7, with the name derived from "Uniplexed Information and Computing Service" as a pun on Multics. Unix's hierarchical file systems, pipes, user permissions, and process isolation became foundational concepts still used in modern operating systems.

Real-Time Military Systems: The Parallel Evolution

While general-purpose systems evolved toward interactive computing, military requirements drove development of real-time operating systems with fundamentally different priorities. The Navy began development of NTDS using transistorized digital computers in 1956, deploying the system in October 1961 on USS Oriskany carrier and USS King and USS Mahan destroyers.

NTDS was designed by the Navy under Don Ream's direction to automate collection of combat data into an overall tactical picture, using multiple identical computers working together in real time. The system was primarily driven by manual radar data inputs from operators and provided automated interchange of the tactical picture across ships via radio links—an unprecedented electronic communications network operating 25 years before the commercial internet.

The AN/USQ-20, or CP-642B, was designed as a more reliable replacement for the Seymour Cray-designed AN/USQ-17, with the first batch of 17 computers delivered to the Navy starting in early 1961. UNIVAC delivered 241 CP-642B units to the Navy and Foreign Military Sales with over 40 variations including water-cooled, air-cooled, solid-mounted, and shock-mounted configurations.

Engineers and technicians entered programs primarily for test and maintenance directly into these systems—demanding hands-on work in cramped equipment spaces aboard ships, often in rough seas, with limited diagnostic tools. The AN/UYK-7, the standard 32-bit Navy computer starting in 1970, used integrated circuits with 18-bit addressing and could support multiple CPUs and I/O controllers, with three CPUs and two I/O controllers being a common configuration.

From NTDS to Aegis: Automated Combat Systems

NTDS was the inspiration for the Aegis system in the 1980s. Analytical work for Aegis had been done as early as 1958 by Richard Hunt of Johns Hopkins Applied Physics Laboratory, who used threat models to determine future environments that would need to be countered by U.S. naval forces.

By 1969, APL had built and tested AMFAR (advanced multi-function array radar), the precursor to the AN/SPY-1A, a key enabler of the Navy's Aegis Combat System. The guided-missile cruiser USS Ticonderoga (CG-47) was the first Navy vessel to feature the Aegis combat system in 1983, allowing the ship to track and engage multiple airborne threats.

Johns Hopkins University Applied Physics Laboratory served as technical direction agent for Aegis, providing systems engineering and testing throughout the program's evolution. The highly automated Aegis represented a quantum leap beyond NTDS's manual radar input model.

Cooperative Engagement Capability: Network-Centric Warfare

The CEC concept was conceived by Johns Hopkins University Applied Physics Laboratory in the early 1970s, originally called Battle Group Anti-Air Warfare Coordination, with the first critical at-sea experiment occurring in 1990 and CEC becoming a Navy acquisition program in 1992.

Cooperative Engagement Capability is a real-time sensor netting system that enables high quality situational awareness and integrated fire control capability. CEC combines data from multiple battle force air search sensors on CEC-equipped units into a single, real-time, composite track picture, making jamming more difficult and allocating defensive missiles on a battle group basis.

CEC represents the culmination of decades of Navy real-time systems development, evolving from NTDS's ship-centered tactical picture to fully distributed, network-centric engagement capability—mirroring the broader operating system evolution from centralized mainframes to distributed cloud systems, but with combat's added constraints.

Enterprise Systems: VMS and Windows NT

VAX/VMS was first announced by Digital Equipment Corporation alongside the VAX-11/780 minicomputer on October 25, 1977, with Roger Gourd leading the project and Dave Cutler, Dick Hustvedt, and Peter Lipman as technical project leaders. VMS systems were widely deployed for scientific computing, including acoustic signal processing at Hughes Aircraft, where DEC VAX/780 computer centers provided robust platforms for signal analysis.

Windows NT 3.1 was released on July 27, 1993. Developed under Dave Cutler, who brought expertise from Digital Equipment Corporation's VMS operating system, NT was designed as a modern, multipurpose OS independent of MS-DOS legacy. The connection between VMS and Windows NT was direct—Cutler's team brought fundamental VMS design principles to Microsoft's architecture.

Graphical Interfaces and Mobile Computing

Microsoft Windows evolved from MS-DOS in the mid-1980s as a graphical operating system. The desktop metaphor made computers accessible to non-technical users, transforming computers from specialist tools into consumer products.

iOS was unveiled in January 2007 alongside the first iPhone and released in June 2007. The Open Handset Alliance, established on November 5, 2007, brought together Google, device manufacturers, and wireless carriers to develop Android, introduced on September 23, 2008, with the HTC Dream as the first commercially available Android smartphone.

Mobile operating systems required fundamental redesigns: aggressive power management, touch-optimized interfaces, sandboxed applications for security, and context awareness based on location and environmental sensors.

Cloud and Virtualization: Computing Without Boundaries

Container technology ramped up significantly in 2017, with major companies supporting the open-source Kubernetes container orchestration tool, cementing its position as the default technology. Kubernetes, introduced by Google as open source in 2014 and now managed by the Cloud Native Computing Foundation, automates deployment, scaling, and management of containerized applications.

Containers are lightweight software packages containing all dependencies to execute applications, virtualizing only software layers above the operating system level unlike virtual machines which virtualize entire machines down to hardware. By 2021, 96% of participating organizations were using or evaluating Kubernetes and container technology according to the Cloud Native Computing Foundation annual survey.

This represents a philosophical shift from owning hardware to treating infrastructure as ephemeral, rented, and globally distributed—"infrastructure as code" where deployments become reproducible and automatically scalable.

Conclusion: Military Necessity, Commercial Success

This seven-decade journey encompasses multiple parallel trajectories: general-purpose systems evolving from batch to time-sharing to interactive computing; real-time systems progressing from NTDS to Aegis to distributed engagement capabilities; and specialized systems serving scientific communities. Each addressed different requirements but converged toward distributed, network-centric architectures.

The classification of Colossus until 1975 meant computing's origin story was told incorrectly for three decades, crediting American innovation while obscuring British cryptanalytic achievements that predated ENIAC by two years. Similarly, the parallel evolution of military real-time systems—designed for guaranteed response times and mission-critical reliability rather than general-purpose computing—remains largely absent from consumer-focused computing histories.

The foundational concepts persist: time-sharing, virtual memory, process isolation, hierarchical file systems, real-time determinism, and distributed computing. Whether managing commercial databases, controlling weapon systems, or orchestrating global cloud infrastructure, modern operating systems build upon principles established by military necessity, academic innovation, and commercial imperatives during computing's critical formative decades.

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The Pre-Operating System Era: Computing's Military Origins

Contrary to the video transcript's portrayal, computing's history began not with toggle switches in the 1950s, but with three parallel urgent military requirements during World War II: ballistics calculations, code-breaking, and nuclear weapons development. These applications fundamentally shaped computing's trajectory.

Ballistics: ENIAC and the Army's Computational Crisis

ENIAC was designed by John Mauchly and J. Presper Eckert to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory, addressing a critical bottleneck in weapons deployment. The world's first electronic digital computer was developed by Army Ordnance to compute World War II ballistic firing tables at Aberdeen Proving Ground, Maryland.

Groups of women nicknamed "computors" struggled to keep up with demand for artillery firing tables, which required accounting for wind speed, humidity, temperature, muzzle velocity, air density, and elevation. A skilled person with a desk calculator could compute a 60-second trajectory in about 20 hours, while the Bush differential analyzer produced the same result in 15 minutes, but ENIAC required only 30 seconds.

Cryptanalysis: Colossus and the Birth of Electronic Computing

Cryptanalysis represents perhaps the single most important driving application in early computing history, yet it remained classified for decades. Colossus, the first large-scale electronic computer, went into operation in 1944 at Britain's wartime code-breaking headquarters at Bletchley Park. Tommy Flowers spent eleven months designing and building Colossus at the Post Office Research Station, Dollis Hill, with Colossus Mk 1 delivered to Bletchley Park in late December 1943/January 1944 and working in early February 1944.

Colossus was built to carry out a fundamental stage of the Tunny code-breaking process at electronic speed, cracking encrypted German military transmissions based on electric teleprinter technology that encrypted top-level messages from Hitler and his army high command in Berlin. By the end of the war, 63 million characters of high-grade German communications had been decrypted by 550 people helped by ten Colossus computers.

Colossus predated ENIAC by two years, making it arguably the world's first programmable electronic digital computer. Experts have suggested that the Bletchley Park code breakers may have shortened the war by as much as two years. However, not until 1975 when the first information about Colossus was declassified could the story begin to be told, meaning Colossus was absent from computing history for three decades.

273 women recruited during World War II to operate Bletchley Park's Colossus machines were decidedly not secretaries, but operated custom-built machines to help decrypt German messages encoded using sophisticated Lorenz cipher machines. The cryptographers determined which patterns to run, while the "Wrens" (Women's Royal Naval Service) entered programming using switches and telephone-exchange plugs—a process called "pegging a wheel pattern."

Winston Churchill ordered Bletchley Park machines destroyed after the war and kept operations secret under strict injunction that was not lifted even after the war ended. Two Mark II Colossus machines were moved to Government Communications Headquarters but eventually dismantled as well. The approximately ten thousand men and women who worked at Bletchley had been sworn to secrecy and honored their commitment so effectively that few outside the project knew about the code-breaking work for more than thirty years after World War II ended.

The Legacy of Wartime Computing

These three parallel efforts—ballistics at Aberdeen Proving Ground, cryptanalysis at Bletchley Park, and nuclear calculations at Los Alamos—established computing as essential to modern warfare and national security. After World War II, several Bletchley Park team members joined Manchester University, including Alan Turing in 1948, contributing to postwar computer development. The classified nature of Colossus meant that ENIAC received credit as "first" for decades, distorting computing history until declassification in the 1970s.

NASA Langley later relied heavily on computational methods for planning orbital trajectories during the space race, but the foundation—electronic digital computing driven by military necessity—had been laid at Aberdeen, Bletchley Park, and Los Alamos during World War II.

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Updated Historical Corrections section:

Historical Corrections and Clarifications

The video transcript contains several critical errors and omissions:

1. Cryptanalysis Omission: The transcript completely omits Colossus and Bletchley Park's code-breaking efforts—arguably the most important driving application in early computing history. Colossus went into operation in 1944, two years before ENIAC, but remained classified until 1975.

2. Computing Origins Misrepresentation: The video suggests computing began with 1950s toggle-switch mainframes, omitting three critical World War II applications: ballistics calculations at Aberdeen Proving Ground, cryptanalysis at Bletchley Park, and nuclear weapons calculations at Los Alamos.

3. IBM 790 Error: The transcript references "IBM 790" which does not exist. The IBM 7090, announced in late 1958 with first installation in December 1959, was a transistorized mainframe.

4. Missing Systems: The transcript omits DTSS, IBM TSO, DEC VMS, and critically, the entire branch of Navy real-time operating systems (NTDS, Aegis, CEC) representing parallel evolution with distinct requirements.

Complete Source List

Operating Systems History - General

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Colossus and Bletchley Park

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ENIAC and Ballistics Computing

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IBM Systems

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Time-Sharing Systems

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Unix and Multics

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DEC VAX/VMS

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45. Cutler, Dave. "VMS Design and Implementation." Digital Equipment Corporation, 1988.

Windows NT

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Mobile Operating Systems

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Cloud and Containerization

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NTDS (Naval Tactical Data System)

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CP-642B / AN/USQ-20

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AN/UYK-7

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Aegis Combat System

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78. Johns Hopkins University Applied Physics Laboratory. "Defining Innovations: Aegis Combat System." https://www.jhuapl.edu/our-work/defining-innovations/aegis-combat-system

79. U.S. Navy. "Aegis Weapon System." Naval Sea Systems Command. https://www.navsea.navy.mil/Home/Warfare-Centers/NSWC-Port-Hueneme/What-We-Do/Acquisition-Integrated-Weapons-Systems/Aegis/

80. Friedman, Norman. "The Naval Institute Guide to World Naval Weapon Systems." Naval Institute Press, 2006.

Cooperative Engagement Capability (CEC)

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SAGE and Early Real-Time Systems

87. Wikipedia Contributors. "Semi-Automatic Ground Environment." Wikipedia. https://en.wikipedia.org/wiki/Semi-Automatic_Ground_Environment

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Historical and Technical References

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91. Campbell-Kelly, Martin, and William Aspray. "Computer: A History of the Information Machine." Basic Books, 2004.

92. Levy, Steven. "Hackers: Heroes of the Computer Revolution." O'Reilly Media, 2010.

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94. Tanenbaum, Andrew S., and Herbert Bos. "Modern Operating Systems." Pearson, 4th edition, 2014.

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Total: 96 formal citations

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Acknowledgment: This article incorporates firsthand technical corrections from Stephen, a Senior Engineer Scientist with over 20 years of specialized expertise in radar systems and aerospace defense, whose career spans the evolution described: using IBM System/360 at University of Maryland (1965); implementing DEC VAX/VMS systems at Hughes Aircraft for acoustic signal processing; hands-on programming and maintenance of Navy UNIVAC CP-642B and AN/UYK-7 computers for NTDS; and insights into JHU/APL's development of Aegis and Cooperative Engagement Capability. His corrections regarding the primacy of cryptanalysis and the operational realities of maintaining real-time combat systems corrected significant omissions in the original video transcript.