Hooray for the sockets interface | APNIC Blog

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In 1983, the University of California, Berkeley campus (UCB) released version 4.2 of its UNIX operating system, the Berkeley Standard Distribution (BSD). For many people, this is the ‘epoch event’ that defines the birth of online services, because it is the version that released the BSD ‘sockets’ model of networking into the world. In effect, the ‘right place, right time’ combined for computing systems and an operating system to run on them. This led to a massive increase in access to network services worldwide.

The installation of this first ubiquitous network approach was by tape, which you got in the mail.

To modern eyes, this may seem strange, given that modern operating system installation is most often a network-driven event. If you do not download a full ISO image or bootable VMDK disk image from the network, you tend to download a smaller system that bootstraps from the network. This is normal — the network is assumed.

Back in the 1980s, while ‘a network’ might exist, it was both too narrow — dial-up telephone at speeds as low as 1200 or 2400 baud — and lacked common protocols to specify how to find and fetch content. Even if you had access to ‘the network’, it was difficult to reliably retrieve something like the binary code of a new operating system. It looked different almost everywhere.

Sockets are a large part of the story that changed this. After sockets, networked UNIX systems began to look broadly consistent. We arrived at a more standardized model of network access.

Prior versions of BSD for PDP-11 minicomputers, dating back to 1978, had been released to the research community worldwide on tape: 30 copies of the code for version 1, and 75 copies for version 2. The system was released under a licence issued on behalf of ‘the Regents of the University of California’, and it carefully limited liability and user rights. You received the code in the post on a reel of tape.

If you wanted to update your code, the Regents required continuity of the people signing the licences. This caused problems, as academic roles often shifted between department members in ways the Regents’ lawyers did not anticipate.

When you received an operating system like this on tape, it consisted of a linear series of recordings. Each was denoted by an ‘End of Transmission’ (EOT) marker, which you could skip to reach the next block. In effect, a stream of bytes was read in a fixed format.

To begin, you were provided with minimal hex code to enter by hand at a switch console. This depended on your computer architecture. The code bootstrapped by reading the first tape block into memory, after which you jumped into memory to run it as a bootstrap loader.

Entering the hex meant setting switches across a 16-bit field — up or down, on or off — checking them against a printed listing, and then committing them to memory one address at a time. It was slow and error-prone. The true end-of-tape marker was a silver label that triggered a photoelectric diode to stop the tape motor.

After loading the bootstrap loader, you could format a disk and unpack tape archive (TAR) data from the tape onto it. This encoded all operating system files onto the local disk. The process took most of a day. If you needed to recompile the system, for example, to add device drivers, it could take two or three days. Despite this, many people accepted the cost to gain access to a UNIX system.

Version 4.2BSD shipped with several significant changes. These included bug fixes, an improved filesystem quota method, and symbolic links — which initially puzzled users accustomed to hard links. Alongside these was the Berkeley sockets networking system, developed under contract from the Defence Advanced Research Projects Agency (DARPA). At the time, it wasn’t clear how significant this was.

Before sockets

Before this, access to network services on UNIX relied on programs such as cu or tip. These acted as terminal emulators, sending characters over serial ports to modems. Many early modems were acoustic couplers attached to telephone handsets using Velcro — one part was a microphone, the other a speaker. You connected by dialling the phone.

Tools like the Unix-to-Unix Copy Program (UUCP) used scripts that called cu or similar tools to establish connections, then transferred data. Even using cu was slow. Terminal types in tools such as the vi editor (a BSD innovation by Bill Joy, later a co-founder of Sun Microsystems) reduced screen updates to suit slow links.

UUCP was how we sent mail, read network news, and received (small) files. For much of the research community, it effectively was the network. Others used IBM BITNET or systems such as the UK Science and Engineering Research Council Network (SERC), later JANET (Joint Academic Network), which operated over X.25 data networks.

Sockets and the UNIX file model

Sockets changed all this. They...