[Coco] Coco drives single and double side question.

[Frank Swygert]

You had me confused too, but Rogelio and Robert Gault cleared it up... I think! You really need to download "Tandy's Little Wonder". Click on the link, then click on the READ ME FIRST file, then the two PDF files. You'll have a wealth of basic (and advanced!) info for the CoCo. I believe there is a program in there to access the back sides of drives, among other mods. 

I'm going to reiterate some of what Rogelio and Robert said here....

1. DECB (Disk Extended Color BASIC -- the CoCo disk system) was designed to operate up to four single sided 35 track (~158K) disk drives, but was really only expected to operate with two. The original drive cables had teeth removed from the connector and the drives had all the drive select jumpers on. The position the drive was in on the cable then determined what drive number it was. The last position was drive 0, the "middle" (between controller and drive 0 connectors) was drive 1. Later cables (for the CoCo3, and the last of the CoCo2 systems) had all the teeth in the connectors and the drive select jumpers were used. 

2. Standard 360K double sided drives will work, but only the "front" side will be active unless DECB is modified. This can be done permanently by burning a new ROM chip, or temporarily by running a program to modify DECB. 

3. Early Tandy drives will usually access 36 tracks, not just the standard DECB 35, and some will access 37 or 38. Later Tandy drives were 40 track, but DECB was never modified to access more than 35 for backward compatibility. 

3. A common modification program is ADOS (or ADOS3 for the CC3). This has lots of options! You go through the program listing, edit the options you want, then: A - run the program and use the options from memory (temporary) or B - have the program burned into a ROM chip to be placed in the controller (permanent). Other "DOS" programs such as JDOS did basically the same thing, but Art Flexser's ADOS was the premiere DECB modification program -- pretty much a standard. 

4. Accessing the back of drives 0 and 1 as drives 2 and 3 is one common mod, accessing the full 40 tracks is another. Using the back sides as 1 and 3 allows backups from 0 to 1 as if two standard drives were being used. 

5. To access four single sided drives just make a cable and plug them in. 

6. The drive controller can physically access THREE double sided drives. Tandy wisely used the side select line as the drive 3 (fourth drive) line. This allows the controller to access the "back" head of three drives. DECB, however, is limited to four drives total, so the third drive isn't accessible. Under OS-9, however, this feature becomes very useful! 

7. You can have three drives physically connected, DECB will just ignore the third one IF it's been modified to access the back sides of two as 2 and 3. Boot OS-9 and it ignores the DECB ROM -- it will access all three drives, both sides, as single or double sided drives (depending on the drives and Os-9 drivers used). I had two 360K drives in my system with ADOS burned to access the back sides as 2 & 3, and a 720K 3.5" drive connected that only OS-9 would access. All were connected to the same controller by the same cable.

8. I can't think of anything else! D/L the book, it has ALL the answers in it, and you can always ask here! 

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Date: Tue, 08 Jan 2008 21:43:09 -0500
From: Ghislain Harvey <ghislainharvey at videotron.ca>

What I really want is that my system react as if I have 2 single side drive.

I have 2 double side drive.
So that's why I say DIR2 will give me the same thing as DIR0

-- 
Frank Swygert
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