IBM and System/360

📜 Background: IBM and System/360

Before OS/360, IBM developed separate hardware and software for each computer model. Programs written for one system wouldn’t run on another.

In 1964, IBM introduced the System/360, a revolutionary family of compatible computers. All models used the same instruction set, which allowed software to run across the entire product line.

To support this, IBM needed a common operating system, which became OS/360.

🛠️ Development of OS/360

1. Announcement

April 7, 1964: IBM announced the System/360 family and OS/360.

2. Challenges

OS/360 was massively ambitious, far more complex than any prior IBM OS.

Estimated at 1,000,000 lines of code (huge for the time).

Development led by Fred Brooks, who later wrote “The Mythical Man-Month” based on this project.

Experienced:

3. Project Management Lessons

Brooks’ Law: “Adding manpower to a late software project makes it later.”

OS/360 became a case study in software engineering.

🧰 Editions and Versions

There were multiple configurations of OS/360, tailored to different system sizes:

PCP (Primary Control Program)

MFT (Multiprogramming with a Fixed number of Tasks)

MVT (Multiprogramming with a Variable number of Tasks)

IBM System/360 Models: Versions, Release & EOL Dates

Model —>Announced —>First Shipped —>Discontinued —>Notes
Model 30 —>Apr 7 1964 —>Jun 1965 —>Jun 22 1970 —>Entry-level, full 360 ISA bitsavers.org+15en.wikipedia.org+15en.wikipedia.org+15righto.com+2en.wikipedia.org+2en.wikipedia.org+2

Model 40 —>Apr 7 1964 —>Apr 1965 —>Oct 7 1977 —>Mid-range workhorse
Model 20 —>Nov 18 1964 —>Apr 1966 —> — —>Partial compatibility, withdrawn 1970s
Model 44 —Aug 16 1965 —>Jun 1966 —>Sep 24 1973 —>Specialized for real-time/scientific
Model 50 —>Apr 7 1964 —>Aug 1965 —>Mar 15 1977 —>Balanced business/science
Model 60 —>Apr 7 1964 —>Apr 22 1965 —> — —>Rare, quickly superseded
Model 62 —>Apr 7 1964 —>Apr 22 1965 —> — —>Rare, superseded by 65
Model 65 —>Mar 1965 —>1965 —>Mar 1974 —>Virtual memory support, multiprocessing
Model 67 —>1965 —>1966 —> — —>First with DAT (virtual memory)
Model 20–70 —>Apr 1964 —>Varies –>Replaced by higher models
Model 75 —>~1965 —>— —>— —>High-end, 1 MIPS performance via cache
Model 85 —>1968 —>— —>— —>First with integrated caching
Model 91 —>Jan 1966 —>1967–68 —> — –>Early superscalar, scientific CPU
Model 95 —>— —>— —> — —>Thin-film variant of Model 91
Model 22 –>Apr 7 1971 —>Jun 1971 —>Oct 7 1977 —>Cost-reduced Model 30 replacement
Model 25 —>Jan 3 1968 —>Oct 1968 —>Oct 7 1977 —>Bridge model with microcode storage
Model 95 —>1968 —> — —> — —>Thin-film memory variant

🗓️ Important Context

System/360 Line Span: Announced April 7, 1964; active shipments from 1965 to around 1978 si.edu+15en.wikipedia.org+15en.wikipedia.org+15.

Official Discontinuation: Family officially retired in late 1977, with the last models (25 & 22 & 40) withdrawn on Oct 7, 1977 en.wikipedia.org+6gunkies.org+6en.wikipedia.org+6.

Successor Systems: System/370 introduced in 1970, ushering in virtual memory architecture.

🧩 Key Features

Batch processing

Job Control Language (JCL) for submitting jobs

Spooling (Simultaneous Peripheral Operations OnLine)

Device independence

Multiprogramming (in MFT and MVT)

Basic memory protection

Early support for time-sharing (in extensions)

🌍 Impact and Legacy

Standardized architecture: Pioneered cross-system compatibility.

Software engineering influence: OS/360’s troubled development birthed the field of software project management.

Mainframe dominance: Foundation of IBM’s control over enterprise computing for decades.

Still running: z/OS, its modern descendant, runs mission-critical systems worldwide (e.g., banking, airlines, governments).

📚 Further Reading

“The Mythical Man-Month” by Fred Brooks (1975) – essential book on software engineering

IBM Archives – rich source of historical documents

Computer History Museum – detailed retrospectives

2

🧩 1. Basic Information

Field —>Description
OS Name —>OS/2
Developer —>Originally IBM & Microsoft, later IBM alone
First Released —>1987
Latest Version —>eComStation 2.2 (~2017) / ArcaOS 5.1 (2023)
License Type —>Proprietary (IBM), later commercial licensed derivatives
Supported Platforms —>x86 PCs (Intel 80286+), limited PowerPC experiments
Still Active? —>✅ Yes (via ArcaOS, maintained for legacy apps & embedded use)

⚙️ 2. Kernel & Architecture

Kernel Type: Hybrid (microkernel elements + monolithic services)

Designed for protected mode, preemptive multitasking on Intel 286/386+ CPUs

Supported virtual DOS machines (VDMs) to run multiple DOS apps simultaneously

Later versions had symmetric multiprocessing (SMP) support on multi-core CPUs

🌟 3. Key Features

Advanced GUI: Workplace Shell, a fully object-oriented desktop interface

True preemptive multitasking & multi-threading long before mainstream Windows had it

Long file names, HPFS file system (High Performance File System) with journaling and extended attributes

Could run DOS apps in separate protected sessions (no crashes like Windows 3.1)

Excellent support for early networking & LANs

Later versions included Java VM, voice navigation, OpenDoc components

📈 4. Version History & Important Milestones ✅

Version / Milestone —>Year —>Description
OS/2 1.0 —>1987 —>Text mode, jointly developed by IBM & Microsoft
OS/2 1.2 —>1989 —>Introduced HPFS file system
OS/2 2.0 —>1992 —>IBM-only, 32-bit, true multitasking, could run Windows 3.1 apps
OS/2 Warp 3 —>1994 —>Popular version, improved GUI, Internet support
OS/2 Warp 4 —>1996 —>Voice dictation, Java integration, last major IBM release
eComStation —>2000s —>Based on Warp, sold by Serenity Systems
ArcaOS —>2017± –>Modern commercial spin-off with USB 3, SMP & UEFI support

🎯 5. Target Audience & Use Cases

Corporate desktops: banking, insurance, ATMs (still run OS/2 Warp today)

Factories & embedded systems: OS/2 is stable and still controls many machines

Retro computing enthusiasts: love its Workplace Shell & old OS/2 games/apps

Specialized deployments: ArcaOS keeps OS/2 alive with modern drivers for old systems

✅ 6. Pros & Cons

Pros —>Cons
Advanced multitasking & memory —>Limited native app ecosystem after Windows took over

protection (ahead of Windows 95)
Extremely stable for critical apps (banks, ATMs) —>Proprietary, fewer modern features
Highly efficient file system (HPFS) —>Minimal USB & modern hardware driver support until ArcaOS
Still maintained via ArcaOS —>Complex licensing for new installs

🎨 7. UI Demo & Visuals

Boot splash: “OS/2 Warp” logo on blue screen

Workplace Shell desktop: draggable folders, shadows, object properties

Launching multiple DOS/Windows 3.x apps in separate windows

OS/2 config.sys settings & WarpCenter dock bar

ArcaOS modernized desktop with USB drives and Firefox running

📦 8. Ecosystem & App Support

Could run:

Community ports of modern apps (like Firefox ESR builds) exist in ArcaOS

🔐 9. Security & Updates

Strong user-space isolation — DOS/Windows crashes didn’t bring down the OS

File system (HPFS) protected against corruption with journaling & extended attributes

Modern patches & drivers maintained by Arca Noae (ArcaOS vendor)

Legacy fixes still occasionally released for banking & POS installations

🌍 10. Community, License & Development

License: IBM proprietary, sold to Serenity (eComStation), now Arca Noae (ArcaOS)

Still has a global enthusiast & retro community — sites like OS2World, EDM/2 maintain archives

Numerous conferences & sessions at retro computing events

Source code still mostly closed, though IBM released parts of the Workplace Shell APIs