Talk:QBUS backplanes

Height vs. Width in DEC Backplanes Section

Is it alright to change the table heading "Height" to "Width" in the DEC Backplanes section? "Height" in this context should refer to the module's size (dual, quad, hex). Glitch (talk) 16:48, 28 July 2024

Tricky question! DEC has changed the orientation of PDP-11 boards (and thus backplanes, into which they plug) three times, over history. And clearly, which dimension you are measuring with 'height' will change with board orientation. Originally, in the -11/20, they were vertical, with the contact fingers at the top. Then, starting with the -11/45, for a long time, they were vertical, but with the contact fingers at the back edge. (I.e. rotated 90 degrees around the board-normal horizontal axis, from that of the -11/20.) There were other ones mixed in there, e.g. the 5-1/4" cabinet for the -11/05, where the boards were horizontal. Starting with the -11/03, horizontal became the usual board orientation (although rotated 90 degrees around the vertical axis, from that of -11/05) - except for the -11/84, where they went back to vertical. So, there is no single, universal, correct, word for the 'parallel to the board' axis.

What we generally do, in most troublesome cases, is to use exactly the terminology that is in the original DEC documents (often with an explanatory note). Looking in the 'Microcomputer Product handbook', pg. 59-1 (diagram on pg. 69-4), 'Height' is defined as the distance across the board, from the contact finger edge, to the handles edge; 'Width' is defined as the distance across the board, from one edge, to the other. (For the mid-period orientation, above, the correct term for the "module's size" is the 'height' - e.g. 'hex-height board'.)

The column you want to change - the number of slots - is called the 'Length' in the 'Microcomputer Product handbook'. So, if you want to change the heading, that's really the only available choice under the 'use exactly the terminology that is in the original DEC documents' system. There is currently an explanatory note: "'Height' is the number of slots", which we should make sure to keep in sync with whatever we do.

PS: We follow the Wikipedia system for talk: pages; please sign all posts (using the ~~~~ special form); that way, if someone reads this a year from now, they can see instantly who said what, without having to look in the history. Jnc (talk) 19:21, 28 July 2024 (CEST)