Some details of the disk Interface:
The actual dimensions of a 3″ disk are thickness 3/16; width 3 1/8; length 3 29/32 and they come in a hard plastic case which is larger. The 3″ disks are called CF2, whatever that means. To compare the actual size of a 3.5 disk is 1/8 thickness; 3 9/32 wide and 3 9/16 long.
The actual interface unit is in several cases. First is the twister board to adapt the Spectrum/TC-2068 unit to the TS-2068 computer. It is 7.5″ wide with the TS-2068 feedthru coming off to the right and the TC-2068 feedthru going straight out from the TS-2868 computer. The twister board is about 4.5 inches deep. Plugged into the twister board is a box, the interface box, measuring 3.75″ deep by 3.625″ wide and 1.187″ high. It plugs into the twister board. On the back is a 15 pin D male socket. From the male socket is a coiled cord that goes to the controller. The controller, the disk drive and the power supply are all identically sized and can be stacked. All boxes are silver in color. Their dimensions are 2.750 highs 6.25 deep and 4.750 wide. The power supply has three disk drives type connectors to supply power to a maximum of 2 disk drives and the controller. If more disk drives are added then it would be necessary to have another power supply for the added on disk drives. The controller has two 9 pin D sockets for the serial interfaces.
One outstanding thing is that there are no exposed boards or wires and everything is self contained. With the T/S twister expansion connector it is possible to continue to use the regular accessories that you are used to using.
Comparing the four disk interfaces, the LarKen, the Oliger, the AERCO and the ZEBRA or TOS in operation, the ZEBRA is more like the AERCO in that the disk has to BOOT automatically to get the disk system going. To use the TOS, you put a disk in the drive but not seated and turn on the power supply for the interface but not the computer. After turning on, push the disk to seat and the disk drive light will flicker and when it stops, turn on the computer, the disk drive light comes on again and if you watch closely you will see the screen flash with the normal logo plus a line that says TOS 1985. You get the AUTOSTART program if there is one or else the disk directory. The LOAD/SAVE and other commands are like the Oliger in that you use an * instead of / to use the disk system.
I have successfully gotten a 3.5 drive to work with the interface in the one sided 40 track mode. Later I discovered that I could FORMAT to 80 tracks double sided but I did not get the four disks SAVEd to double sided 80 tracks. I did get them to save to 40 tracks single sided on the 3.5 disks. For a reason that I don’t understand the program “BACKUP” will only copy from a single sided 40 track disk to the same type disk. While I was working with the system it died and apparently the edge card connector that plugs onto the twister board split and the fingers no longer made contact with the twister board. I shipped the entire outfit to Nazir Pashtoon for repair.
I later received a letter from Jack Dohany. I ordered a pair of drives (3.5 new and tested) plus a 64K controller for the ZEBRA system so that I could use CP/M. After I get the system going I will get some CP/M disks for the ZEBRA system. I have found the 3″ drives to be dependable and while I have no proof, I believe that they are 30ms in head step rate. At least they seem slow. I received 5 disks from George Chambers and while they had programs on them they were not TOS. I moved the drive to the other computer and tried the LarKen, and there was the directory. Of course they were single sided but a few were FORMATted to 42 tracks. I copied them to 5.25 disks and have plans to reFORMAT the disks to TOS when I get the system up and going again.
While I had the drive on the other computer I did check the rpm and found the drive to be a very uniform rpm 297 for all eight of the first eight revolutions on turn on.
In a letter I received from Jack Dohany he stated that in FORMATting from DFM that if you select 40 tracks it is always FORMATted to single sided and that if you FORMAT to 80 tracks it is always FORMATed to double sided. So that is solved. That is in the FDD EPROM.
The program BACKUP is only for copying 40 tracks single sided to 40 tracks single sided. I did not get a chance to test the copying routine on DFM since the interface died about then. When I get the interface back I will FORMAT disks to 80 track on the 3.5 drive and try out the copy routine.
I have read and reread the FDD manual and now await the arrival of the interface to try out things. 0/0