Browse Prior Art Database

DEC PDP-10-IMLAC communications system (RFC0190) Disclosure Number: IPCOM000007196D
Original Publication Date: 1971-Jul-13
Included in the Prior Art Database: 2002-Mar-05
Document File: 17 page(s) / 25K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

L.P. Deutsch: AUTHOR


This report describes an operational system for communicating textual display information between a main-site computer and a remote-display processor.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 17% of the total text.

Network Working Group                                         P. Deutsch

Request for Comments: 190           Xerox Research Center, Palo Alto, CA

NIC: 7135                                                   13 July 1971


   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

      (henceforth TENEX).

      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

      two machines.

(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

   short vectors.

      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


(II)  Facilities.

   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

      multiple areas.

   When a user (program) requests a display area, he specifies how many

   text strings he will want to display in it.

      Each string...