By Nermeen Nabil Khear 
It is easy to forget that many technology juggernauts weren’t always the only game in town. Ethernet seems ubiquitous today, but it had to fight past several competing standards. VHS and Blu-ray beat out their respective competitors. But what about USB? Sure, it was off to a rocky start in the beginning, but what was the real competition at that time? SCSI? Firewire? While those had plusses and minuses, neither were really in a position to fill the gap that USB would inhabit. But [Ernie Smith] remembers ACCESS.bus (or, sometimes, A.b) — what you might be using today if USB hadn’t taken over the world.
Back in the mid-1980s, there were several competing serial bus systems including Apple Desktop Bus and some other brand-specific things from companies like Commodore (the IEC bus) and Atari (SIO). The problem is that all of these things belong to one company. If you wanted to make, say, keyboards, this was terrible. Your Apple keyboard didn’t fit your Atari or your IBM computer. But there was a very robust serial protocol already in use — one you’ve probably used yourself. IIC or I2C (depending on who you ask).
I2C is robust, simple, and cheap to implement with reasonable licensing from Philips. It just needed a little tweaking to make it suitable for peripheral use, and that was the idea behind ACCESS.bus. [Ernie] tracked down a 1991 article that covered the technology and explained a good bit of the how and why. You can also find a comparison of A.b, I2C, and SMBus in this old datasheet. You can even find the 3.0 version of the spec online. While DEC was instrumental in the standard, some of their equipment used SERIAL.bus, which was identical except for using 12 V power and having a slightly different pinout.
The DEC Station 5000 was an early adopter of ACCESS.bus. From the user’s guide:
In theory, one ACCESS.bus port could handle 125 devices. It didn’t have a hub architecture like USB, but instead, you plugged one device into another. So your mouse plugs into your keyboard, which plugs into your printer, and finally connects to your PC.
The speed wasn’t that great — about 100 kilobits per second. So if ACCESS.bus had won, it would have needed to speed up when flash drives and the like became popular. However, ACCESS.bus does sort of live even today. Computer monitors that support DDC — that is, all of them in modern times — use a form of ACCESS.bus so the screen you are reading this on is using it right now so the monitor and PC can communicate things like refresh rates.
We love to read (and write) these deep dives into obscure tech. The Avatar Shark comes to mind. Or drives that used photographic film.
This articles is written by : Nermeen Nabil Khear Abdelmalak
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