diff --git a/Readme b/Readme
index b44cbed..02a922b 100644
--- a/Readme
+++ b/Readme
@@ -63,10 +63,16 @@ Documentation
 -------------
 
 The manuals for 1st Edition UNIX are available here:
+http://www.cs.bell-labs.com/who/dmr/1stEdman.html, and
 http://www.bitsavers.org/pdf/bellLabs/unix/UNIX_ProgrammersManual_Nov71.pdf
 
 Some documentation of the internals of the 1st Edition UNIX are available here:
-http://www.bitsavers.org/pdf/bellLabs/unix/PreliminaryUnixImplementationDocument_Jun72.pdf
+http://www.bitsavers.org/pdf/bellLabs/unix/PreliminaryUnixImplementationDocument
+_Jun72.pdf
+
+Details of the PDP-11/20 architecture and its peripherals can be found at:
+http://www.bitsavers.org/pdf/dec/pdp11/handbooks/PDP1120_Handbook_1972.pdf
+http://www.bitsavers.org/pdf/dec/pdp11/handbooks/PDP11_PeripheralsHbk_1972.pdf
 
 The C compiler from 2nd Edition UNIX is also installed and works, but the
 language is a very early dialect of C. You may find the 2e manuals useful: