8" Floppies

Jerome Fine replies: I don't know if this will help, but here goes. I was using the DSD 880/30 - an RL02/RX02 compatible. It holds a single 8" floppy drive which can use both SSDD and DSDD diskettes (soft-sectored). I found that since I had a small number of DSDD diskettes and the media seemed to be identical, the ONLY difference that I could observe was that the index hole was in a different location. I wired a DPDT switch into the index hole detection circuit. In the left hand position, it was wired to duplicate the existing circuit. When I wanted to REVERSE the operation, I used the right hand position of the switch. In the second position, the index hole for a SSDD diskette caused the drive to route the signal from the sensor to the portion of the circuit which normally detected the signal from the DSDD index hole. Thus, the drive and the software "THOUGHT" that a DSDD media was present and I was able to use a SSDD diskette as a DSDD diskette without having to punch a second set of index holes. The use of a DSDD diskette as a SSDD diskette is also possible if that is useful - I never found it to be needed. Naturally, this required that I do a LLF (Low Level Format) on both sides of the diskette. This the DSD 888/30 is able to do all by itself and that solved the problem. As for using the DSDD diskette with DEC software, V4.00 of RT-11 had some code which showed how to access the "second" side and use the floppy drive as an RX03. I used that code as a starting point since I also wanted to allow the DYX.SYS device driver in a 22-bit environment with V5.03 of RT-11. Note that the DSD 880/30 and the DEC RX02 with an M8029 can use only the first 1/4 MByte (18 bit addresses) when a transfer is made to/from the DMA silo from/into a buffer in the memory of a PDP-11. Software in the DYX.SYS device driver is able to use all 4 MBytes of the PDP-11 physical address space in a manner totally transparent to the user of the device driver. I realize that Sridhar is not using RT-11, but I just thought I might mention the above for those of you that do. Sincerely yours, Jerome Fine