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Newly discovered Unix V4 tape
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Diomidis Spinellis ☛ blog dds: 2025-12-23 — An initial analysis of the discovered Unix V4 tape
The Fourth Research Edition Unix came out of the famous AT&T Bell Laboratories in November 1973. A significant development it introduced was the rewriting of large parts of the system’s kernel in a high-level language (early C) rather than PDP-11 assembly language. The tape contains a complete system dump, including both source code and the compiled binaries and kernel. For inclusion in the Unix history repository, I removed the binaries, to match what is normally put under source code version control.
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Tom's Hardware ☛ 52 years later, only known copy of Unix v4 recovered from randomly found tape, now up and running on a system — first OS version with kernel and core utilities written in C
The only known complete copy of Unix v4 has been recovered from a tape found at the University of Utah.
Followup on this:
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Recovered Unix v4 tape quickly yields a usable operating system — nostalgia addicts can now boot up Unix v4 in a browser window
Nostalgia addicts can now get their Unix v4 fix in a browser
Valnet:
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52 years later, UNIX V4 has been rediscovered and digitized
Linux, macOS, FreeBSD, Android, and other operating systems can trace their lineage back to the early commercial versions of Unix. One of the missing links in that chain, UNIX Fourth Edition, is now publicly available after being lost for decades.
UNIX Fourth Edition, also known as UNIX V4, was first released in November 1973. It was developed by AT&T and Western Electric, and it marked the first time that C code was used in the kernel instead of primarily assembly language. Early versions of Unix were built for mainframes and 'minicomputers'—the microcomputer revolution that powered the Apple II, Commodore 64, BBC Micro, and other 8-bit personal desktops was still years away. The Linux kernel, FreeBSD project, and other Unix-like clones didn't show up until the 1990s.
For decades, there were no known copies of UNIX Fourth Edition, with only some source code and manuals surviving to the present day. That changed when a nine-track tape reel containing UNIX V4 was discovered in a storage room at the University of Utah's Kahlert School of Computing. The tape was delivered to the Computer History Museum, and has now been digitized and uploaded to the Internet Archive.
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UNIX V4 is back: I booted into the 1973 OS and it made me weirdly happy
Last year, researchers at the University of Utah found a copy of Unix lying around on a 9-track magnetic tape. It's special because that version of Unix was lost until it was recovered from that magnetic tape 52 years later. The researchers managed to successfully reconstruct it, and then they made the copy public. Anyone can download it and run it inside a virtual machine. So I did just that, and it made me so giddy to use it.
What is UNIX V4, and why should you care?
If you care about computer history at all, Unix lore is utterly fascinating. There was a time when operating systems were tied to their hardware. There was no way to move an operating system to hardware that it wasn't specifically programmed to run. Imagine only being able to install Android on one specific phone model or Windows on just one specific hardware configuration. We take it for granted today, but Unix V4 made 'portable' operating systems possible.
Earlier versions of Unix were written in Assembly code, so those Unix systems were tied to the machines they were written for. With V4, the developers rewrote the entire operating system in C, which made the code machine agnostic. Later versions perfected this approach but Unix V4 is where it all began. The first rewrite wasn't a commercial product, so there were only a few research copies ever made. That's why this version, the first one to use the C programming language, was thought to have been lost. All that survived was the programmer's manual. This 'missing link' in Unix history was eventually discovered in a storage closet during a routine clean up. As far as we know, this is the only copy that survived.