Shook DSI FDC-II system

This Web page last updated Dec 8 2016. This page discusses Jeff Shook's Digital Systems Inc. floppy-disk system for his IMSAI. He's the original owner, bought it new from DSI. He has been kind enough to provide that history, in Feb-Mar 2008. and is quoted and used with his permission. Edits by me are in []'s. The system, DSI and IMSAI is still in degrees of operation. On Feb 10 2010, I added some photos of Jeff's system; and a note from 2015, from Jeff about the original CP/M version obtained with his system. In 2016, I point to some of my DSI hardware.

On another Web page, I discuss the company "Digital Systems Inc." and their product, the FDC-1 - among the earliest floppy controllers for the S-100 bus, and the first controller product to include CP/M. Jeffrey W. Shook describes his FDC-II there.

Related: In 2013, and again in 2016, I acquired Digital Systems Inc. hardware. In 2013 I obtained a DS FDC-3 system - drives, controller, interface. In 2016, I obtained another FDC-3 controller, pulled from a DS Inc. cabinet. Check my Digital Systems restoration Web page for details and progress.

The home page for my history of Digital Research, CP/M, and related work is at this link. Contact information for me is at the end of this Web page. - Herb Johnson

- Herb Johnson

How I got my Digital Systems FDC-II floppy disk system.
Jeffrey W. Shook, Feb 2008

"The LICA (Long Island Computer Association) 8080 Users Group of which I was a member had a discussion of floppy disk systems at the December 17, 1976 meeting. (This was subsequently mentioned in the January 1977 LICA STACK newsletter.) At that time only two members had floppy systems, an Intel MDS and a 6800 system with an INNOVEX floppy. By July 1977 the 8080 User group member list had six members with a Digital Systems FDS, one [with an] ICOM, and one [with an] IMSAI floppy system."

"I had used paper tape, Kansas City cassette, and Tarbell tape interface to store programs and data. I needed a faster, more convenient way to store programs and data for my consulting business. [So] I decided to purchase a floppy disk system and CP/M."

"I read all I could find about CP/M and floppy systems in the magazines and decided to purchase a Digital Systems FDC-2 drive system and CP/M 1.3 directly from Digital Systems. The disk system arrived around the 1st of March, 1977. I spent a couple of days becoming familiar with the BIOS configuration and integrating the i/o routines supplied on the CP/M 1.3 disks from Digital Systems into the BIOS for my IMSAI 8080. Finally it worked and I was able to boot CP/M. Using the CP/M system was wonderful except for ED. The FDC-2 system is still working now over 30 years later with only minor repairs to the Shugart floppy drives."

- Jeff Shook

Update in 2015: I found a post by Jeff Shook in Usenet newsgroup comp.os.cpm on Dec 8 2013: "Yes, I have CP/M 80 1.3 for the Digital Systems FDC-2 dual 8 in drive system, which I used with my Imsai from 1977 until about 2008."


Here's a photo of the top of the Digital Systems cabinet. The cabinet is sitting sideways and the controller card is visible. Here's a closer view of the controller card. Jeff added a copper-clad board between the controller and the drives, because he found some 1's were read when there were long strings of zeros. Apparently the card picked up noise from the drives.

In his IMSAI is the Digital Systems interface card, shown here. The top of the card is visible and is labled "HB-1.3". At one time, Jeff read out the PROMs which contain the microcode of the controller; here's a photo of the reader he created to do that. - Herb Johnson, Jan 2010

Information about the FDC-II

Descriptions, documents, code and manuals for Digital Systems Inc. floppy controller systems are on this Web page. Jeff Shook has kindly provided a number of these documents.

Discussion with Herb Johnson

Jeff discussed his purchase information, which shows he obtained the system the first few days of March 1977. He also provided a photo of the lable of his system diskette. I commented to him, "I see the diskette lable is hand-written, [and] says "Ser # 1-140" which I take to be Torode's license number one plus some tally of customers probably 100-140 (unless he really sold 140 systems in less than a year!)."

Jeff repsonded: "I don't think that 140 systems is too surprising. As I mentioned in my account of the FDC-II system the LICA 8080 User Group members had six of them in July, 1977. Assume 20 such user groups around the country making similar purchases and that would amount to 120 units."

Herb: "When did you order the Digital Systems product? When did you first find out about it?

Jeff:" I am not sure of the order date. I assume it was before the beginning of March, 1977 since I have notes dated March 3 about how the disk system was packed. I sent the first check to Digital Systems but it could have been earlier. I think that someone in LICA had purchased a system and I saw or heard about it. And of course I read BYTE magazine from cover to cover so I would have seen the advertisment there."

[Note: The January 1977 BYTE had a small block ad for Digital Systems, an image of it is on my DRI history summary page.]

In March Jeff added: "[I] found some of the early programs I wrote just after installing the DSI disk system to my IMSAI. The first one is an adaptation of a memory test for 8K memory boards formerly loaded from paper tape. It is dated March 10, 1977."

Herb: "What are the dimensions of the card? Anything distinctive on the back, codes or stickers or whatever? Date codes on chips?"

Jeff: " The card is 10 inches across, 11 inches from front to back (Edges with connectors). On the back is only "FDC 2.2" and "Digital Systems" and a single white 30 ga jumper wire of unknown purpose. I will have to check my notes. It might be the Computer Mart of NJ patch for head unload.

Herb: "[From the image you sent me,] the date codes on the chips seem to go to mid 1976 (7626, the 26th week of 1976). You might look for later dates if you can.

Jeff: "The latest date code I found is 701 on the IC at location H4. This is only three months before I received the system." [Note: that code would be 1977, week 01. - Herb]

Floppy systems mentioned by Jeff Shook

A Web search on "Innovex floppy" says Byte had a press release on their minifloppy 410 or 420 system in their Oct 1977. magazine. A US patent 4327421 filed May 1976 mentions the Innovex 220 floppy drive. Innovex the company still exists as a Nasdaq stock company, which makes "flexible circuit solutions". They were testing floppy drives as early as 1973, according to a former "engineering technician" there at the time (Mark Robillard, resume on the Web). But as I say on my DRI history summary page, a number of companies offered floppy systems add-ons in 1973, 1974 and 1975.

The iCOM floppy drive system is referenced on this Web page. The IMSAI and IMDOS floppy system and operating system, a licensed version of CP/M worked on by Kildall, is discussed on this Web page.

Contact information:

Herb Johnson
New Jersey, USA
To email @ me, see see my ordering Web page.

Copyright © 2016 Herb Johnson, portions by Jeffrey W. Shook as noted