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* The 1973 edition for the [PDP-8/e, PDP-8/f, and PDP-8/m](https://archive.org/details/bitsavers_decpdp8hanHandbook1973_79671711) is not entirely relevant to the PDP-8/I we're primarily concerned with here on this web site, but they did refine the tutorial material quite a bit over the earlier editions, so it is sometimes helpful to read the equivalent material in this newer edition when trying to figure something out. Just be aware that not everything applies to a PDP-8/I. (PDF, 76 MB.)
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**Footnotes and Digressions**
1. The PDP-8 does have one programmer-accessible register that isn't an even multiple of 3 bits, the single-bit "link" register, but we won't be talking more about that register in this article. The term "link" in the article does not refer to this register.
1. The PDP-8 does have one programmer-accessible register that isn't an even multiple of 3 bits, the single-bit "link" register, but we won't be talking more about that register in this article. The term "link" in this article does not refer to the PDP-8's Link register.
2. Thus the term [octet](https://en.wikipedia.org/wiki/Octet_(computing\)), which unambiguously refers to a group of 8 bits.
3. Yes, "versions," plural. There were actually 3 major [versions of ASCII](https://en.wikipedia.org/wiki/ASCII#History), published in 1963, 1964, and 1967. Since the original PDP-8 came out in 1965 and the PDP-8/I model came out in 1968, you can see that the development of these computers coincided quite nicely with the development of ASCII itself. Thus, the PDP-8/I is one of the first machines that was aware from inception of what we now think of as 7-bit ASCII.
4. The most common terminal used with PDP-8s and other machines of its era was the Teletype Model 33 ASR, the "ASR" referring to the Asynchronous Send and Receive version of the Model 33. Although you will commonly see that terminal type referred to as an ASR-33, that is not its [proper](https://en.wikipedia.org/wiki/Teletype_Model_33#Model_33_ASR_vis-.C3.A0-vis_ASR-33) name.
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