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The Digital Group
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I am no longer active in this hobby for the foreseeable future. 
I will no longer maintain or update the website, but I will leave it accessible to the web for as long as possible (years).


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Digital Group Systems

The Digital Group was a Denver Colorado based company founded in August of 1974 by Dr. Robert Suding and Dick Bemis to sell microcomputers designed by Suding. DG computers were among the most advanced microcomputer systems available at the time. They offered users a choice of CPU's that enabled upgrading or swapping processors to run software written for any of the four most popular processors available: The Zilog Z80, The Intel 8080, the Motorola 6800, and the 6500 series from MOS Technology. DG computers included video, cassette tape, and keyboard interface standard with every system, as well as a simple operating system on tape geared towards programmers. The Z80 and 8080 systems also included several demonstration programs. Notably, The Digital Group Z80 was the first computer to use the still very popular Z80 microprocessor chip. 

Digital Group computers were designed to be more user friendly than other computers available at the time. Loading software on an audio based system was as simple as pressing play on a cassette tape player and then the reset button on the system to load a selected application or operating system. Disk system (Diskmon) or data tape system (Phimon) startup was as simple as pressing the reset button, and requesting the desired application by name with the keyboard.

The software applications available were numerous, and varied from business applications to hobby and gaming. The popularity of the DG platform was such that programmers were eager to write applications for it, and the standardization of the hardware allowed for an immediate and large potential customer base. 

Popular until the very end, Digital Group failed in August of 1979 due to management and parts supplier troubles, not a lack of customer interest or product orders. Co-founder Dr. Robert Suding recalled that at the time of the bankruptcy, DG had thousands of product information requests and orders waiting to be filled.

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 system 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 the Altair system. Of course, to even 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. ($$$) By contrast, Digital Group systems included a video and cassette interface and a keyboard as standard equipment with all of their systems.

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 operating 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 processor card with 256 bytes of ROM and 2k of static RAM memory on board, video/cassette card, and I/O card. These cards fit into a large standard or small 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. The cabinet was optional, and many DG owners chose to build their own cabinets, or order them from another supplier. 

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! Still, many hobbyist really like the blinking lights, and even though the front panel added little functionality, they did add geek glamour!

Click here to see Flyers
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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The original

Click here to see the Bytemaster page!
The Mini Bytemaster, the last DG system offered.

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.

Digital Group systems did not use the Altair S-100 buss like so many other clones of the day. This is because dg systems were not Altair clones, and were not inspired nor derived from Altairs. They were an original design by Dr. Robert Suding, designed around the same time as the Altair, but as history would have it, the Altair made it to market first. 

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Dr Robert Suding, designer of all digital group stuff, pays a visit to my collection.


Hardware Documentation

I have several detailed pages related to DG systems and hardware, as well as documentation and and advertising -- Be sure to follow the links at the top or left side of this page!

 Digital Group Beginnings

The Digital Group was founded in 1974 shortly 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" (commonly seen in advertisements as "the digital group" -- all lowercase characters). 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. An interesting side note: according to Dr. Suding, he never modified his own Mark-8 as was described in the packet.

The success of Mark-8 packet sales led to the development of the first "all Digital Group" designed computer, built using the new Intel 8080 chip. Many of the innovations in the packet were expanded upon in DG computer 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 very useful additions. 

As part of my collection, I have the original hand drawn schematics and sketches made by Dr. Suding as he designed the Digital Group computer system electronics. These can be seen on the DG Documentation page.


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, so there was no need to key in the program by hand-- a common requirement for software of this time. Really! Software from this era was largely distributed as a "listing", printed (or even typed by hand!!) on paper. Many software offerings of the time were sold or just as often, given away as source listings only, requiring the buyer to key in what could be hundreds or even thousands of lines of the program code themselves! Very few titles were available as punched paper tape--readable by expensive hardware at 10 characters per second. Even fewer were offered on cassette or disk. DG was way ahead of the pack, for a while anyway!

I have a section of my web site dedicated to DG software with downloadables, be sure to check it out!

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. I even tried to exchange it for the Z-80, but was turned down in a letter from Dick Bemis. Out of necessity, I wrote hundreds of my own programs, and modified dozens of others to run from other systems. (SWTPC, Altair 680, etc.) I quickly came to love my 6800, in spite of the isolation from most other DG owners!

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My 6800 system with flip up card cage.

Most of the software I wrote 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.

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. Follow the link to see the pics!


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Copyright 2008 Bryan's Old Computers
Last modified:
October 16, 2009