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PDP-8 Frequently Asked Questions (posted every other month)
Section - What about the LINC/8 and PDP-12?

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Wesley Clark and Charles Molnar, then at Lincoln Labs, built the LINC, or
Laboratory INstrumentation Computer, as a personal laboratory computer,
finishing the first in March 1962.  The machine was developed in response
to the needs of Mary Brazier, a neurophysiologist at MIT who needed better
laboratory tools, and it was a followup to the Average Response Computer,
an 18 bit special purpose machine built in 1958 for the same purpose.
When Lincoln Labs decided that the LINC did not fit their mission, in
January 1963, the project moved to MIT, and then in 1964, to Washington
University in St Louis.  The National Institute of Health funded the
project as an experiment to see if coumputers would be a productive tool
in the life sciences.  By the end of 1963, 20 LINCs had been built and
debugged, many by their eventual users.

Over 24 LINC systems were built by customers before late 1964 when DEC
began selling a commercial version (see Computers and Automation, Nov.
1964, page 43).  By the time DEC introduced the LINC-8, 43 LINC systems
had been installed (see Computers and Automation, Mar. 1966, page 34).
In total, 50 LINC systems were built, 21 by DEC, 29 by customers (see
Digital at Work, page 52).  A photo of the last LINC in production use
is available from http://www.mit.edu:8001/people/ijs/epl/LINC.html
Wesley Clark wrote a history of the LINC, "The LINC was Early and
Small", published in "A History of Personal Workstations," ACM Press,
1988, page 347.

The LINC was the first 12 bit minicomputer built using DEC hardware.
Like the PDP-5 and other early DEC computers, it was built with System
Modules, DEC's first family of logic modules.  Along with the CDC 160,
it paved the way for the PDP-5 and PDP-8.

When compared with the PDP-8, the LINC instruction set was not as well
suited for general purpose computation, but the common peripherals
needed for lab work such as analog-to-digital and digital-to-analog
converters were all bundled into the LINC system.  Users judged it to
be a superb laboratory instrument.

One of the major innovations introduced with the LINC was the LINCtape,
designed by Tom Stockebrand scaled down from an experimental tape drive
developed for the TX-2 at Lincoln Labs.  LINCtapes could be carelessly
pocketed or dropped on the floor without fear of data loss, and they
allowed random access to data blocks.  Stockebrand improved on this idea
slightly after he came to DEC, where the improved idea was called
DECtape; DECtape was widely used with all DEC computers made in the
late 1960's and early 1970's.

The motives behind the development of LINCtape were the same motives
that led IBM to develop the floppy disk almost a decade later, and in
fact, DECtape survived as a widely used medium until DEC introduced the
RX01 8 inch floppy disk drive around 1975, and even after this, DECtape
was only slowly phased out.

Within a year of the introduction of the PDP-8, DEC released the LINC-8,
a machine that combined a PDP-8 with a LINC in one package.  The
success of the LINC-8 led DEC to re-engineer the machine using TTL
logic in the late 1960's; the new version was originally to be called
the LINC-8/I, but it was sold as the PDP-12.  Both the LINC-8 and the
PDP-12 had impressive consoles, with separate sets of lights and
switches for the LINC and PDP-8 halves.

The success of the LINC-8 also led to the development of a clone, the
SPEAR micro-LINC.  This machine used Motorola MECL integrated circuits
and was available for delivery in (June 1965? this date must be wrong!).

The LINC-8 and PDP-12 could run essentially any PDP-8 or LINC program,
with the exception of the few programs that relied on the primitive
interrupt structure of the original LINC architecture; on the LINC-8,
all interrupts were handled by the PDP-8 side of the hardware.  Because
the LINC-8 and PDP-12 had instructions for switching between modes, a
new body of software was developed that required both modes.

One feature of LINC and LINC-8 software is the common use of the graphic
display for input-output.  These machines were some of the first to
include such a display as a standard component, and many programs used
the knobs on the analog to digital converter to move a cursor on the
display in the way we now use a mouse.

Various versions of LAP, the Linc Assembly Program, were the dominant
assemblers used on the LINC; the original version of LAP was a cross
assembler written on the TX-2.  WISAL (WISconson Assembly Language) or
LAP6-W was the version of this assembler that survived to run on the
PDP-12.  Curiously, this includes a PDP-8 assembler written in LINC code.

LAP6-DIAL (Display Interactive Assembly Language) evolved from this on
the PDP-12 to became the dominant operating system for the PDP-12.  The
8K version of this is DIAL MS (Mass Storage), even if it has only two
LINCtape drives.  These were eventually displaced by the OS/8 variant
known as OS/12.

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