PDP-11/20 vd one that just says pdp 11 what are the date differences?? OEM?

In a message dated 2/22/2016 11:50:15 A.M. US Mountain Standard Time, cisin at xenosoft.com writes: On Mon, 22 Feb 2016, Paul Birkel wrote: When everybody realized and accepted that there would be more than one sub-model, and decided that it might be handy to be able to tell them apart. There may have been some holdouts in some departments, such as silk-screening the panels. By analogy, the phrase "single density" didn't originally exist. After "DOUBLE-density" was developed, THEN "single density" needed a name. Although just sticking with "FM" and "MFM" would have been a lot better! (Although I guess that it was inevitable that marketing would invent "HD", instead of "double data transfer rate MFM".) There were even a few companies that freely intermingled HEADS V density! Intertec/Superbrain decided to call their 5.25" 40 track DSDD, "QUAD density", because it was twice the capacity of the 40 track SSDD! Then, when they added an 80 track DSDD, they caalled that "SUPER density", abbreviated "SD"! So, if you encounter an alien disk labelled "SD", it might be 720K/800K, not 100K. Similarly, if you were to search ancient archives, the phrase "World War TWO" was first used BEFORE there was any mention of "World War ONE". It wan't until a second happened, or was expected, before anybody had any reason to declare the "Great war"/"World War" to be "nuber ONE". So, the use of any sort of "first" name doesn't occur until "second" is expected. Or WW1 was also referred to as the "war to end all wars" some good name sequence comparisons here Ed#