Computer Desktop Buses

Computer Buses Daisy Chaining factor

My blog entry on the LiDE 30 scanner brought back the Commodore Bus, and made me wonder, having a connector that allowed daisy chaining used to be common (Apple Desktop Bus, SCSI), in the past, but that idea seems to have faded away, the omnipresent USB bus does not, although some devices can include a hub.

So I did what any computer geek would do, I draw a graph. I took all peripheral buses that I ever had on a device I owned and that I remember. The sheet with all the data is here (I did not know there was a master list at that point). This does not include network ports (LocalTalk, Ethernet, Wifi), memory expansion standards like, SD-Card, PCMCIA, and wireless protocols like or Bluetooth. The X axis shows the year the standard for that interface was released, the Y axis is the theoretical bandwidth – as the scale is logarithmic, the different between theoretical and practical bandwidth is not super relevant. The width of a bubble is the number of devices that can be daisy chained (controller included), 1 means a point to point connection. ADB stands for Apple Desktop Bus.

First observation, daisy chaining is still here, Thunderbolt can be daisy chained, and I²C is going nowhere. You could argue that I²C is not really an peripheral bus, but it kind of is, for things like Arduinos, but also within the various video standards (VGA, DVI, HDMI, etc). Second, if you ignore I²C, daisy chaining seems to be a feature of the high speed interface: already on the Commodore 64, the Commodore Bus was for the floppy disk drive and the printer, the audio cassette interface was a slow, point to point thing. Third, all the wired bus standards below the bandwidth of USB 1.2 (Serial, Parallel, ADB) have effectively been replaced by plain USB, which was the goal…

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