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* The Forth Interest Group *
****************************
In the late 1970's, Northern
California was afire with the early
rumblings of the Computer Revolution.
Groups of interested individuals such
as the "Home Brew Computer Club" were
meeting to share interests and
experiences. Magazines such as Radio
Electronics published step-by-step
instructions on how to build your own
video display terminal, and even how
to build your own microcomputer
system.
Due to the high cost of memory and
low level of VLSI integration,
typical "homebrew" computers were
very resource-constrained
environments. Echoing back to the
first generation computers, there was
insufficient memory to concurrently
support an editor, assembler and
linker. Mass storage was slow and
expensive, so many homebrew systems
used paper tape or audio cassette
tapes for I/O. Although some BASIC
language products were available,
they were typically very slow, and
incapable of supporting significant
programs. The stage was thus set for
something else to meet the expanding
needs of these hardy explorers and
"early adopters."
Forth had been born and bred to
exploit the minimal facilities of
resource-constrained systems. It
carried neither the excess baggage of
a general solution nor a requirement
for an existing file or operating
system or significant mass storage.
As Forth was used to tackle more and
more difficult embedded computer
applications, it started to claim the
attention of the Northern California
homebrew computer enthusiasts.
Bill Ragsdale, a successful Bay Area
security system manufacturer, became
aware of the benefits of microFORTH,
and in 1978 asked FORTH, Inc. to
produce a version of microFORTH for
the 6502. FORTH, Inc. declined,
seeing much less market demand for
microFORTH on the 6502 than the more
popular 8080, Z80 and 6800 CPUs.
Ragsdale then looked for someone with
the knowledge of microFORTH and
intimate familiarity with the 6502 to
port a version of microFORTH to the
6502. He found Maj. Robert Selzer,
who had used microFORTH for an AMI
6800 development system on an Army
project and was privately developing
a standalone editor/assembler/linker
package for the 6502. Selzer wrote a
6502 Forth assembler, and used the
Army's microFORTH metacompiler to
target compile the first 6502
stand-alone Forth for the Jolt single
board computer.
Selzer and Ragsdale subsequently made
substantial modifications and
improvements to the model, including
exploitation of page zero and
stack-implicit addressing
architectural features in the 6502.
Many of the enhancements that
characterized the later public-domain
versions were made during this
period, including variable-length
name fields and modifications to the
dictionary linked-list threading. A
metacompiler on the Jolt could target
a significantly changed kernel to a
higher address in memory. A
replacement bootable image would then
be recompiled by the new kernel into
the lower boot address, which could
then be written out to disk. At this
point, Ragsdale had a system with
which to meet his professional needs
for embedded security systems.
During this period the Forth Interest
Group (FIG) was started by Ragsdale,
Kim Harris, John James, David
Boulton, Dave Bengel, Tom Olsen and
Dave Wyland. They introduced the
concept of a "FIG Forth Model," a
publicly available Forth system that
could be implemented on popular
computer architectures.
The FIG Forth Model was derived from
Ragsdale's 6502 system. In order to
simplify publication and rapid
implementation across a wide variety
of architectures, a translator was
written to convert Forth metacompiler
source code into text that, when
input to a standard 6502 assembler,
would replicate the original kernel
image. In this way, neither the
metacompiler nor its source code
needed to be published. This is an
important point. Forth
metacompilation is a difficult
process to understand completely. It
requires the direct manipulation of
three distinct execution phases and
object areas, and is not something
that a casual user wanted or needed.
By publishing assembler listings, the
Forth Interest Group was able to
encapsulate a Forth run-time
environment in a manner that could be
easily replicated and/or translated
to the assembly language of a
different computer architecture. It
was the intention of the original
team of implementers to thus
stimulate the development of
compatible Forth systems and the
appearance of new vendors of Forth
products.
After the 6502 FIG Model was
published, FIG implementers published
compatible versions for the 8080 and
6800 microcomputers and the PDP-11
and Computer Automation
minicomputers. Over the years,
volunteers added other platforms and
documentation. The 1982 Forth
Encyclopaedia by Mitch Derick and
Linda Baker provided an exhaustive
333-page manual on FIG Forth, with
flow charts of most words. In 1983 an
ad in Forth Dimensions, the FIG
newsletter listed: RCA 1802, 8080,
PACE, 6502, 8086/88, 6800, 6809,
9900, Nova, Eclipse, VAX, Alpha
Micro, Apple II, 68000, PDP11/LSI11
and Z80.
Today there are several thousand
members of the Forth Interest Group
in over fifteen countries. Since
1980, FIG has sponsored an annual
conference called FORML (Forth
Modification Laboratory), an
educational forum for sharing and
discussing new or unproven proposals
intended to benefit Forth, and for
discussion of technical aspects of
Forth. Its proceedings are available
from the Forth Interest Group
To read more about Forth & Forth Inc
go to:
http://www.forth.com/resources/
evolution/index.html
TO COMMODORE FREE MAGAZINE
FROM FORTH, Inc.
http://www.forth.com/resources/
evolution/index.html
"Permission to copy without fee all
or part of this material is granted
provided that the copies are not made
or distributed for direct commercial
advantage, the ACM copyright notice
and the title of the publication and
its date appear, and notice is given
that copying is by permission of the
Association for Computing Machinery.
To copy otherwise, or to republish,
requires a fee and/or specific
permission."
As Commodore Free states its purpose
as "A free to download Magazine
dedicated to Commodore computers"
that satisfies the requirement for no
commercial advantage so you have
permission.
Please contact me if you have any
other questions about Forth, our
company, or its history.
Best regards,
Leon H Wagner
President
FORTH, Inc.
Dave Jaffe
=================================