An adaptor is a hardware or software device that adapts one format to another. Often the formats are both standards of some sort. Before generalities we describe some specific adaptors.

PDP-10 magnetic tape controller

The PDP-10 was a 36 bit machine built when IBM was building high quality tape drives devoted to a media format comprising 8 bit bytes. Dec and others built special controllers to attach such tape drives to their 36 bit machines. How to square 8 bit bytes with 36 bit words? Their controllers supported three modes of I/O and the reasons for these three is very instructive:
32 bits of one word ↔ 4 bytes on tape
This mode is suitable for PDP-10 programs that must read and write tapes whose format is dictated by the world of machines with 8 bit bytes. No special programming on 8 bit byte machines is necessary.
36 bits of one word ↔ 5 bytes on tape including one 0 nibble
This is good for storing arbitrary blocks of core on tape so as to be retrieved later bit for bit. Special programming on the 8 bit byte machines is necessary to read or write such tape.
72 bits of two words ↔ 9 bytes on tape.
This is most conservative of tape and core space. Special formatting code is likely necessary for both sorts of machines.
The first mode adapts the world of native 8 bit tapes so as to accessible by PDP-10 programs. The 2nd mode adapts blank media and IBM tape drives to to the task of storing PDP-10 core content. The 3rd mode combines the space advantages of both at the expense of possible hair in programs for machines of either persuasion.

Capros web server

Just now the design question of a Capros httpd (web server) program has been raised. Here are some possible goals of such a program: These different architectures can be interdefined and the real question is how to bottom-out.