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System Restoration
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| Digital Group System
Details
This was the "Cadillac of computers". In 1975, when
this system was introduced, Altair system owners were flipping
switches for hours just to watch lights blink on the front panel
of their systems. Digital Group owners were throwing a power
switch and loading an operating system in less than 20 seconds.
The cassette interface, standard with DG systems, loaded
programs at 1100 baud. At the time, this was nearly four times
the speed possible with any other manufacturers tape systems,
and ten times faster than paper tape; the only method available
at the time for loading Micro Soft BASIC onto an Altair system.
Of course, to do that on an Altair, you had to buy a paper tape
reader and an interface. Usually an ASR-33
Teletype and an SIO card. ($$$)
The Digital Group was among the very first to offer computer users
a "warm boot". When switched on, a Digital Group
system was ready to load the op system, prompted by the message
"Read 6800 INITIALIZE cassette" (or similar processor
specific message). As the tape was read, the screen would fill
with the HEX or OCTAL page high address of the byte being
loaded, testing the memory content for correctly loaded data as
each byte was saved.
A basic Digital Group system consisted of three boards:
Interchangeable Z80, 8080, 6800, or 6502 processor card with 2k
of memory on board, video/cassette card, and I/O card. These
cards fit into a standard or mini-motherboard. The standard
motherboard would accept up to three memory cards and a total of
up to four I/O cards. The mini had room for only one memory
card besides the other three required boards. Both motherboards
had a small prototyping area near the processor card, and solder
points for video out, cassette in/out, and power supply
connections. A low current power supply was offered at a modest
price, and the customer could choose from a variety of +5 volt
high current supplies.
As for an Altair style front panel card with blinking lights
and switches... if you just had to have one, schematics were
included with the documentation. These were used mostly for
troubleshooting. The Digital Group system was far too
sophisticated to actually need something like that in normal
operation! |
The Digital Group "System
4", from Flyer #9, Circa 1977.
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My Digital Group "System
4".
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"System 3", as seen
on the cover of Flyer #8, 11/76
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This is one of my restored Z80
systems, before I had a real dg case for my monitor.
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The Mini Bytemaster, the last dg system offered.
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Dr Robert Suding, designer of all
digital group stuff, pays a visit to my collection.
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The Digital Group also offered a very wide range of hardware
accessories. If it was available to computer users at the time,
it was available to DG system owners, and usually first. A users
group of the time reported (and I confirmed in conversation with
Dr. Suding) that within two weeks of the release of the Zilog
Z80 chip samples, Dr. Suding had finalized the design for the
Digital Group Z80 processor card, and had working systems on
display at computer shows. Besting the closest competitor by
weeks if not months. Contrast that with the common practice of
the day, of running ads for a concept product, then using the
money from the customer orders to develop the advertised
hardware.
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Digital Group Beginnings The Digital Group began in
1974 just after Dr. Robert Suding saw the Mark-8 Minicomputer on the
cover of Radio Electronics magazine, and then built one. This was a rare
thing: a working hobby computer. (Made even more rare by the
complexities of the Mark-8 design!) After a successful test, Dr. Suding announced
his achievement, and his willingness to help others do the same. Many
came to see the working Mark-8, and among them, Dick Bemis. A month
later, the two men and their wives, incorporated "the digital
group". The first offering of the new company was "Packet
#1", which was a set of plans to improve the Mark-8, and included
plans for a video and cassette interface, along with ROM listings for a
warm boot (to my knowledge, the very first for a hobby computer), and
software drivers to make everything work. It also included listings for a
simple operating system. The success of Mark-8 packet led to the
development of the first "all Digital Group" designed
computer, the 8080, as described above. Many of the innovations in the
packet were expanded upon in the dg systems; both the hardware and the
software drivers are very similar. The video and cassette plans were
merely improved versions of the Mark-8 packet designs, both very simple,
but surprisingly far more capable than anything available to hobbyist at
the time. The operating system was also a near exact copy, but with some
useful additions. I have, as part of my collection, the original hand
drawn schematics and sketches made by Dr. Suding as he designed the
digital group computer system electronics. As I am able, I will scan and
add these to the archive.
Software
If you owned an 8080 or Z80 system, as did most DG system
owners, then you had access to what might have been the widest
range of software available to any computer owner. The Digital
Group offered at least four versions of BASIC; Tiny, Mini, Maxi,
and Business. A BASIC extension language called OPUS/ONE and
OPUS/TWO were also available, which made for a more powerful
BASIC language than any other I'm aware of, then or now! Users
could also get other languages or operating systems, CONVERS,
PHIMON, DISKMON. The latter two were similar in function to a
simple DOS. In addition to languages and operating systems, The
Digital Group offered text editors, word processors (very
powerful, by the way, with WYSIWYG), assemblers /disassemblers,
and business packages. Oh, yeah - and games. Lots of games,
everyone played games... Microsoft wasn't anywhere near this
level of sophistication with any product they offered at the
time! All of these software titles were supplied on a cassette
or disk, there was no need to key in the program by hand; a
common requirement for software of this era. (Really! Many
software offerings of the time were sold as source listings
only, requiring the buyer to key in what could be hundreds or
even thousands of lines of the program code themselves!)
| My 6800
System
The Digital Group was my computer of choice. In 1976 when I
began a search for my first computer with money in hand, the
Digital Group always came to the top of the list. I wanted a
computer with a boot ROM. (So I wouldn't have to flip switches for
an hour just to get a paper tape reader to load the operating
system!) A cassette interface was a must, and a video based system
instead of terminal I/O seemed like a big plus to me. I chose a
6800 based system because the instruction set seemed more
understandable. Until I owned and built the computer from a kit, I
was unaware that the Digital Group considered the 6800 a bastard
stepchild of sorts, and wrote no software for it beyond the op
system. Out of necessity, I wrote hundreds of my own programs for my
6800, and modified dozens of others to run from other systems. (SWTPC,
Altair 680, etc.)
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My 6800 system with flip up card
cage. |
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Most of my software writings were very small programs that
performed specific tasks. I had scores of computer music
compositions that played from an AM radio placed near the
processor. (Try that with your PC!) I had my computer turning on
lights, sounding alarms, and a dozen other things. I wrote my own
version of BASIC, and my own "Star Trek" game. (You
really didn't own a computer unless you could play Star Trek!)
All of my programming taught me something very important: I
didn't like programming. Oh, I received great satisfaction from
seeing my programs run as I had intended, but I knew that it
wasn't what I wanted to do for a living! I loved the hardware. I
modified my system constantly. I modified my 16x32 character video
card to display 16x64, added a hardware cursor and direct memory
access, scrolling display and a few graphic characters. About ten
years ago I removed most of those mods because the software
drivers were lost and I had no desire to rewrite them. I left the
64 character mod since changing the software I had to support that
was very easy. (You can see part of the mod on the chip just above
the crystal, in the photo of the 32x16 video card below. The
visible mod is part of a clock doubler circuit.)
My system in the photo above is labeled a 6800, but in fact, I
use this system to test and run everything I am working on. The
card cage is hinged for easy access to the underside of the
motherboard. My original power supply was the 6 amp version. Not
enough for a whole lot. I replaced it in the mid eighties with one
I robbed from a PC. The one in the photo is a second replacement.
Much smaller.
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Dr.
Robert Suding
In early 2004, I received an email from Dr. Robert Suding and an offer
to meet and talk about the Digital Group and the early days of personal
computing. Dr. Suding came to my house for lunch and conversation. With
him, he brought the Mini Bytemaster. We talked about all kinds of fun
things, most of which Dr. Suding has already written down and placed on
his own web page: www.ultimatecharger.com/dg.html
Before leaving we made a deal for Mini Bytemaster. It took about an
hour, and the wives finally had to come in and break us up, but we did
make a deal. : ) It was a great time! We took a few pictures and waved
goodbye. (Find my link at the top of this page to see the Bytemaster.)
We then had the chance to get together again at the VCF 7.0 in
November of 2004 and had a good time. Find the link at the top left of
this page to see the pics!
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