Project Updates
Added 2021-03-25 01:57:09 +0000 UTCThis last week has been a bit of a whirlwind of projects. I had buckled down and got a lot of testing done on the SCSI2SD review. But after some last minute developments, that video is actually getting expanded as a comparison between the SCSI2SD and MacSD. The MacSD was something I found out about while researching the SCSI2SD more and I'm being sent one from the designer for the video now. They're being extremely helpful with it and have already been making some updates to their firmware based on some feedback I gave them. It will be here in a few days but I'll need some more time to test it and work out some potential kinks. So that project is going to be a bit farther out now.
After that was set in place I bounced off of a few other projects but none of them really came together for an easy video. Last night I had an idea for a new project after using my test bench for a bit now. I finally got around to trying a Gotek floppy emulator and it's pretty handy, especially in this system with it's variable OSes. But I don't want to give up one of my other floppy drives to connect it and a 4 floppy controller isn't really practical in this system. After a bit of talking with some other people and doing some testing I had the idea in the picture here and laid out a PCB I'll be placing an order for soon.
Floppy drives have "drive select" pins in the interface that the floppy controller uses to choose one drive to work with even though they are all connected to the same cable. I put together a board that takes a floppy connector and breaks it out into two connectors with a switch that will allow you to manually send the drive select signal that was meant for one drive to either of the two. So this should allow you to add more floppy drives to a system, just with some manual intervention. DOS has a feature that allows you to add more floppy drives in confiig.sys manually. With that you can tell it there are multiple drives connected to the same drive select ID which will work perfectly with this. And disk imaging software that uses RAW access to the drives will work even without that. After I've determined that this board works I will be releasing it as open source and anyone will be able to make one themselves.
So all that is to say, I've got a few interesting projects in the works, but none of them are going to be ready soon so I most likely wont have a video ready for Friday. I just wanted to check in with some updates so you know what's coming up.
Comments
MS-DOS has a lesser known feature, DRIVER.SYS, that can be used to add more floppy drives in the CONFIG.SYS file. You can use it to specify a drive type for a given ID and it will assign a new drive letter to the virtual/logical drive in DOS. Here is an example: http://info.wsisiz.edu.pl/~bse26236/batutil/help/DRIVER_E.HTM it's hard to find documentation of the feature, even the 145 page MS-DOS 6.22 manual seems to only have one line of text for it. I think this is a copy of a software help menu that has more info on setting it up: http://www.manmrk.net/tutorials/DOS/help/driver.sys.htm If I have one 1.44MB floppy drive on ID 0 when the system starts up then add the following to CONFIG.SYS: DEVICE=C:\DOS\DEVICE.SYS /D:0 /F:0 When DOS finishes booting I'll have drive A: as a 1.44MB floppy and drive B: as a 360KB floppy but they will both refer to the same physical interface. Then I can use my switch board to manually select which drive the physical interface will access. So I can connect 1.44MB and 360KB drives to my board and flip the switch to change between them depending on what drive letter I want to access.
Tech Tangents
2021-03-25 16:02:43 +0000 UTCTo be pedantic: MS-DOS didn't have a setting for the number of floppy drives in the CONFIG.SYS (or anywhere else) as far as I know. There is a "LASTDRIVE=" option that allowed you to change the number of drive letters to support, but that doesn't determine how many floppy drives you have. At boot-up, DOS would simply call the BIOS to seek the heads of the first two (or four? not sure) floppy drives back and forth to see if they were there. If there was only one floppy drive, it would enable the "virtual B: drive" meaning that DOS would keep track of whether the current diskette in the drive was A: or B: and would let you know when to switch it. And stop everything until you hit a key to continue). Regardless of how many floppy drives there were, there was always an A: and a B: drive letter, so that's why the hard disk (or its first partition) became C:. I think if you had 3 or more floppy drives in the system, they became C: and/or D: and the hard disk would be drive D: or E:. By default, DOS only allowed drive letters up to E: if I'm not mistaken, because the maximum number of floppy drives that DOS would allow was probably 4 and then the hard disk would be E:. No system needs to waste kilobytes and kilobytes of memory just to allow any more drive letters than that, right? So DOS only allocated memory for 5 drive letters and if you were one of those fancy rich schmucks who could afford a second hard disk, you had to use the LASTDRIVE command to reserve space for more drive letters. But that command has nothing to do with adding more floppy drives. Just more drive letters.
Jac Goudsmit
2021-03-25 15:32:55 +0000 UTCTechnically, this will work with anything that has a floppy drive. PCs, Macs, Amigas, keyboards, etc. But that's just for changing drives. But it doesn't add the ability to address new drives in software, it just changes where the existing "virtual floppy" interface points to. DOS has the ability to create multiple "virtual floppy" interfaces pointed at the same drive ID on the cable with different configurations. I don't think NT based Windows does and I haven't tested it much yet so I don't know if Win98 will work either. So, yes, the hardware will work. It will not make the BIOS see a drive B: though. But you may be able to make a virtual drive B: depending on the OS.
Tech Tangents
2021-03-25 14:34:14 +0000 UTCThat’s an awesome idea! I wonder if this would work with later Pentium 3 & 4 motherboards where the manufacturers disabled one of the channels on the “legacy” floppy controller? (I have a Pentium 4 that I wanted to connect two drives to... but I can only have A: for now)
electricitynerd
2021-03-25 14:15:30 +0000 UTC
