Incompatible Timesharing System


The Incompatible Timesharing System (ITS) is an early, influential time-sharing operating system developed at the Massachusetts Institute of Technology (MIT) in the 1960s and 1970s. It was designed to support collaborative computing among multiple users by allowing them to share resources and access data on a mainframe computer. Though it has now become obsolete, ITS played a significant role in the development of early internet technologies and hacker culture.


The phonetic pronunciation of “Incompatible Timesharing System” is:ɪn-kəm-ˈpæ-tə-bəl ˈtaɪm-ˌʃær-ɪŋ ˈsɪstəm

Key Takeaways

  1. Incompatible Timesharing System (ITS) was an early, influential operating system developed at MIT in the late 1960s and used until the late 80s, designed primarily for collaborative work and research in the field of Artificial Intelligence.
  2. ITS was notable for its open, hacker-friendly design that facilitated rapid development and user experimentation, but also made it less suitable for security-conscious environments.
  3. Despite its eventual decline in usage, ITS had a lasting impact on future systems such as Unix, inspiring aspects of their design, features, and overall computing philosophy.


The Incompatible Timesharing System (ITS) is historically significant because it was an early example of a multi-user operating system, developed at the Massachusetts Institute of Technology (MIT) in the 1960s.

ITS allowed multiple users to simultaneously interact with a single computing system, enabling programmers to share resources and collaborate effectively.

This system also played a pivotal role in the growth of hacker culture and the development of various artificial intelligence and computer science projects within the research community at MIT.

Furthermore, ITS contributed to advancements in later operating systems and provided valuable insights into the timesharing concept, which laid the foundation for modern cloud-based services.


The Incompatible Timesharing System (ITS) was an early and influential time-sharing operating system, developed primarily at the Massachusetts Institute of Technology (MIT) in the late 1960s and early 1970s. The primary purpose of ITS was to facilitate the efficient sharing of computing resources among multiple users, providing each user with seemingly simultaneous access to the system. At a time when computers were still relatively scarce and expensive, ITS enabled users — primarily researchers, programmers, and students — to run their applications on a central computer and work in parallel on multiple tasks without needing dedicated machines.

The system revolutionized the usage of computers by enabling collaboration, rapid development, and the emergence of new programming languages and techniques. Far more than a simple resource-sharing mechanism, ITS also encouraged user creativity, customization, and an open exchange of ideas. The system provided an environment that allowed users to tailor their sessions according to individual preferences and facilitated communication among users.

ITS became the platform for numerous groundbreaking developments in computer science, such as the creation of the first version of the Emacs text editor and the Logo programming language. This open approach to computing spurred a spirit of innovation and knowledge sharing, which would eventually contribute to the growth of the hacker culture and the free software movement. By removing the barriers between users and access to powerful computing resources, ITS proved to be an essential step towards the connected, collaborative technologies that we take for granted today.

Examples of Incompatible Timesharing System

The Incompatible Timesharing System (ITS) was an early, influential operating system developed at the Massachusetts Institute of Technology (MIT) in the 1960s and 1970s. Three real-world examples that showcase the impact of ITS on technology are:

Contributions to the development of ARPANET:ITS played a significant role in the development of ARPANET, the predecessor of the modern-day internet. The ITS project pushed for new networking protocols and demonstrated the potential of timesharing, which allowed multiple users to share computer resources on a single computer. ARPANET was essential for researchers to connect and communicate, and ITS enabled groundbreaking work in network technology and dynamic resource allocation.

Influencing the design of Emacs:Emacs, a popular and powerful text editor, was initially developed on the ITS platform. Richard Stallman, who was one of the early Emacs developers, took inspiration from the real-time text-sharing capabilities of ITS, which was essential to his vision of cooperative computing. This laid the groundwork for Emacs to become one of the most adaptable and extensible editors in use today, contributing significantly to the world of software development.

Establishment of the hacker culture:ITS played a major role in shaping the early hacker culture at MIT, which later spread to other university campuses and the wider tech world. ITS fostered an environment where experimentation, collaboration, and freedom were valued. Users of ITS were granted unrestricted access to the system, allowing them to innovate and learn in a hands-on manner. This ethos encouraged people to push the boundaries of what they could do with technology and is still embraced by many in the open source community today.

Incompatible Timesharing System FAQ

Q1: What is the Incompatible Timesharing System (ITS)?

A1: The Incompatible Timesharing System (ITS) is an operating system developed in the 1960s at MIT. It was designed to support multiple users and concurrent processing on a single mainframe computer.

Q2: Why is it called “Incompatible” Timesharing System?

A2: The name “Incompatible” Timesharing System was chosen because it was developed in parallel with the Compatible Time-Sharing System (CTSS) at MIT. While CTSS was designed to be compatible with earlier batch processing systems, ITS was developed without such constraints.

Q3: Who developed the Incompatible Timesharing System?

A3: ITS was primarily developed by researchers at MIT’s Project MAC, which later became the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL). Key contributors include Tom Knight, Richard Greenblatt, and Bill Gosper.

Q4: What programming languages were used on ITS?

A4: ITS supported several programming languages, including assembly language (MIDAS), LISP, and machine language. In addition, it was instrumental in the development of other programming languages such as MACLISP and Scheme.

Q5: What were some significant achievements of ITS?

A5: ITS played a crucial role in the development of ARPANET, which later evolved into the modern internet. It also provided an environment for pioneering work in artificial intelligence, computer graphics, and computer chess.

Q6: Why was development on ITS eventually halted?

A6: By the 1980s, personal computers and Unix-based systems became increasingly popular, rendering ITS less relevant. The last version of ITS, ITS 1705, was released in 1988, and most of the systems running ITS were decommissioned by the early 1990s.

Related Technology Terms

  • Timesharing
  • Operating System
  • Computer Resources Management
  • Multi-User Environment
  • Mainframe Computer

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