DEC PDP-10-IMLAC communications system (RFC0190)
Original Publication Date: 1971-Jul-13
Included in the Prior Art Database: 2002-Mar-05
Internet Society Requests For Comment (RFCs)
This report describes an operational system for communicating textual display information between a main-site computer and a remote-display processor.
Network Working Group P. Deutsch
Request for Comments: 190 Xerox Research Center, Palo Alto, CA
NIC: 7135 13 July 1971
DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM
This report describes an operational system for communicating textual
display information between a main-site computer and a remote-display
The main site machine is a DEC PDP-10 with the BBN paging hardware
The remote machine is a IMLAC PDS-1 (henceforth IMLAC).
Section (1) briefly describes the IMLAC hardware configurations.
Section (II) describes the display facilities presented to the
Section (III) describes the system calls (JSYS calls) implemented
in the TENEX monitor to provide these facilities.
Section (IV) describes the formats of the messages used for
communication between TENEX and the IMLAC.
Section (V) analyzes the division of responsibility between the
(1) Hardware configurations.
The standard IMLAC is a 16-bit minicomputer with 4K of 2 microsecond
core, a cycle-stealing display, an input keyboard, and an
asynchronous serial communication interface.
The display is normally programmed to draw characters using very
The display comes in two major configurations, depending on the
presence or absence of hardware for drawing long vectors.
In the sequel, specifications depending on the configuration will
be flagged LVH or non-LVH respectively.
The I/O system normally does not provide for interrupts when
characters arrive from the serial interface.
Deutsch [Page 1]
RFC 190 DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM 13 July 1971
However, the IMLAC is barely able to keep up with the PDP-10
without this feature, so we were able to persuade the manufacturer
to implement it.
While no special hardware is required for the software described
here, the character interrupt and the SRI-ARC "mouse" and "keyset"
are highly recommended, and the software is oriented towards their
Each display console in the system may be in "display mode" or
"teletype simulation mode".
In display mode, the information displayed consists of text
strings at arbitrary positions on the display face.
In teletype simulation mode, the display shows the last 20-30
lines which would appear on a teletype listing.
A given console may switch between these modes, under program
control, without losing any information.
Regardless of mode, each display has a cursor string which follows
the position of the available pointing device,
The implemented system uses a "mouse" generally, but one console
uses a tablet.
The cursor string may be set by a program, for example to indicate
at what sort of object the user is expected to point.
In display mode, the screen of a given console is allocated to users
in rectangular blocks called "display areas".
This allows users to communicate via a single display split into
When a user (program) requests a display area, he specifies how many
text strings he will want to display in it.