Today, my project to archive all my old Radio Shack TRS-80 Color Computer floppies continues. I will be using Darren Atkinson’s amazing CoCoSDC interface to copy from physical 5 1/4″ floppy disks to disk image files on an SD memory card, all from a computer that first came out in 1980. If you are just joining me, please read the two earlier parts for an introduction.
My previous article concluded with me describing an easy way to backup standard Color Computer floppy disks. Due to limits of affordable floppy drive hardware at the time, the Color Computer’s Disk BASIC ROM was only written to support a 35-track floppy drive. As technology improved (and prices got lower), Radio Shack would switch from using old full-height, belt-driven 35 track floppy drives to half-height 40-track drives. However, to maintain backwards compatibility, Disk BASIC was never updated to use those extra five tracks, meaning that whether you used the first CoCo disk drive introduced in 1981, or the last one sold in 1991, Disk BASIC still treated it as a 35-track, single-sided device.
Almost as soon as 40-track drives were hooked up to a CoCo, users went to work figuring out how to make use of the extra storage potential. Simple patch programs were released that modified Disk BASIC so it could use all 40 tracks. With this patch, you could still read and write to an original 35-track disk, but if you formatted and wrote to a 40-track disk, only users running the same patch could read it. Because of this, through the entire history of the CoCo, virtually all Disk BASIC software released on floppy disk was in the 35-track format.
I was one of those users, so many of my old CoCo disks are 40 tracks. Since the floppy drive hardware emulated by CoCoSDC emulates the original floppy drive interface, the same patches should work to set CoCoSDC Disk BASIC to 40-track mode and then these floppies can be backed up the same way. (Basically, the patch would change the upper limit from 35 to 40, so formatting with the DSKINI command or using the BACKUP command would now access all 40 tracks instead of just 35.)
Problem: If by default, creating a new .DSK image with the DRIVE command makes a 35-track .DSK file, how can you make a 40-track .DSK file?
According to responses from the CoCo mailing list, the designer Darren says you can download a blank 40-track .DSK image file and mount and use it. But, he also said that images will automatically expand if you write past the 35-tracks. Thus, if I have loaded my patches that set Disk BASIC to 40-tracks, then I create a new blank 35-track .DSK image and BACKUP to it, once it writes past the 35th track, it should start expanding the file to become a 40-track image file.
I will be testing this, soon.
Bigger problem: Early on, users figured out that some floppy drives actually could actually write past 40 tracks and get a bit more storage. I tested this on the drive I had at the time, and found I could reliably write up to 42-tracks of data. Somewhere in my archive are old, old floppy disks formatted to 42-tracks. Will CoCoSDC work with these?
I will be testing this soon, too. I hope to find a way to do this entirely from the CoCo without having to put the SD card in a PC/Mac and work with it.
More to come…