Please note that the content of this book primarily consists of articles
available from Wikipedia or other free sources online. The PDP-11
architecture is an instruction set architecture developed by Digital
Equipment Corporation. It is implemented by central processing units and
microprocessors used in minicomputers of the same name. Additional
information is found in DEC's PDP-11 Processor Handbook. The PDP-11's
16-bit addresses can address 64 KB. By the time the PDP-11 yielded to
the VAX, 8-bit bytes and hexadecimal notation were becoming standard in
the industry; however, numeric values on the PDP-11 always used octal
notation, and the amount of memory attached to a PDP-11 was always
stated as a number of words. The basic logical address space was 32K
words, but the high 4K was not populated because input/output registers
on the bus responded to addresses in that range. So originally, a fully
loaded PDP-11 had 28K words.