From ENIAC to Linux: A Complete History of Operating Systems

Early Operating Systems

In February 1946 the ENIAC, the first electronic computer, was built at the University of Pennsylvania. It occupied 170 m², weighed 30 tons, consumed 174 kW and could perform about 5 000 additions per second. Early machines were manually operated with punched cards, resulting in long idle periods.

Batch Processing and Multiprogramming

During the 1950s batch‑processing systems introduced a supervisory program (monitor) that automatically executed a sequence of jobs. This monitor is regarded as the prototype of an operating system. Early batch machines included the IBM 1401 and 7094.

In the 1960s advances in integrated circuits, memory, and I/O devices enabled interrupt and channel technologies, allowing the system to suspend and resume tasks. This gave rise to multiprogramming systems, where several programs could reside in memory and share CPU time, dramatically improving efficiency.

Time‑Sharing and Real‑Time Systems

Multiprogramming evolved into multi‑user time‑sharing systems, allocating short time slices to each user, similar to time‑division multiplexing. Later, real‑time operating systems provided stricter timing guarantees, approaching the modern OS concept.

Multics and the Birth of Unix

In 1964 AT&T, GE, and MIT launched the Multics project to build a super‑time‑sharing OS. Although Multics never met its goals, its monitor concept directly inspired Unix.

In 1969 Ken Thompson at Bell Labs wrote a simple OS (Unics) on a PDP‑7 to run a game. Dennis Ritchie later rewrote Unics in the newly created C language, producing the first fully functional Unix.

Early Unix and BSD

In 1975 AT&T released Version 6 for $20 000. In 1977 Bill Joy at Berkeley packaged the source onto magnetic tape, creating the Berkeley Software Distribution (BSD) line.

Commercial Unix Variants

Major commercial Unix families include Sun Solaris, IBM AIX, HP‑UX, and the open‑source FreeBSD, which later formed the basis of Apple macOS.

GNU Project and Free Software

In 1984 Richard Stallman launched the GNU project to create a free Unix‑like system, releasing essential tools such as gcc, bash, and emacs. The GNU General Public License (GPL) enforces copyleft, requiring source modifications to be published.

Linux Kernel Development

In 1991 Linus Torvalds, a 21‑year‑old student, wrote a 10 000‑line kernel using GNU tools on a MINIX‑based environment and released it under the GPL, calling it “GNU/Linux”. The kernel follows the POSIX standard, ensuring compatibility with most Unix systems.

Linux vs. Unix Licensing

Linux is open‑source software released under the GPL, whereas Unix is a trademarked, historically proprietary system whose source code is owned by various companies (e.g., AT&T, SCO, The Open Group). Linux mimics Unix’s design but contains no Unix code and is not a certified Unix system.

Linux Distributions and Lineage

Linux distributions combine the kernel with system utilities, graphical environments, and applications. They fall into community‑driven and commercial categories.

Early distributions (1993): Slackware, Debian.

Debian derivatives: Ubuntu, Linux Mint, Kali Linux.

Red Hat family: Red Hat Enterprise Linux (RHEL), Fedora, CentOS (rebuild of RHEL sources).

Other notable families: openSUSE, SUSE Linux Enterprise, Arch Linux, Gentoo.

These distributions share a common ancestry, often building upon each other, creating a rich ecosystem of Linux‑based operating systems.