Option #2 is a better way. Leaving an unpowered drive on a drive chain can create problems, since the divers are not properly tri-stated, or drive high for open collector lines. I'd use a double pole double throw switch. Run the two drive select lines to the center contacts, and top two pins to the two drives you're most likely to use at one time, and the bottom two pins to the other pair that are most likely to be used together. Note that you'll want to keep these runs as short as possible. The drive select lines are, IIRC, the middle two wires of the group of four that's typically twisted in a floppy cable. The original IBM AT (and possible XT, I'm not sure) were the instigators in using the twisted cables. It was cheaper to have a Tiawanese cable house make the cables than it was to address the issue of "well, if you want drive A:, you have to unjumper DS1 and move it to DS0. But drive B: has to have DS1 jumpered." From a customer support standpoint, and being able to send drives out, it meant they could pre-configure the jumper for DS1, and be done with it. There are some other approaches: There were some after market cards that support 4 or 8 drives (8 drives as two controllers, which took extra software). IIRC, the BIOS actually has support for 4 drives, but it's the drive select lines that become the issue. I don't have my Book O' Magic Registers handy, but I think IBM left out the other control bit in the drive control register. It may have only been some old 486 and lower motherboards that supported 4 drives, by making the extra drive select bit available in another register. Once manufacturers realized that no one ('no one' being all but the 4 or 5 people a year) wanted 4 floppies in the system, support for it was dropped. If you ever only need one drive at a time to be active, you could use a rotary switch, and switch the drive select line between any of the four drives. Note that putting more than 4 drives on a chain isn't a good idea, since the bus drivers start getting near their loading limits. Those extra signals, even tri-stated, present a bus load, and add capacitance to the signals. What would be slick is to setup some kind of "fast swap" bay, where you plug the drive you want into a carrier, much like these removable IDE drives. Sadly, I doubt any such thing exists for floppies, since for all practical purposes (from a consumer standpoint), floppies are nearing the end of their life span. What with bootable CDs, CD-R, CD-RW, DVD, and the incredibly small capacity of a floppy, I predict they'll be a rare item in 10 years, and only used to support the old collectables. Just try and find 5.25" low density disks anymore. --John

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Perhaps the easiest thing to do would be to get one of those multi-position wafer switches that one sees in A/B/C/D switches for attaching multiple computers to a single monitor/keyboard/mouse and attach one to each drive. That way you can select the drive configuration you want for any two (which is what the PC will support) of the 4 or 5 drives you have. There are other approaches, but this one will produce predictable results, provided you study out the configuration options in advance. BTW, those 3-1/2"/5-1/4" comination drives look like two drives to the controller. There's even an option jumper for selecting which drive is 'A' and which is /'B.' Dick ----- Original Message ----- From: "David C. Jenner" <djenner(a)earthlink.net> To: "Classic Computer Mailing List" <classiccmp(a)classiccmp.org> Sent: Wednesday, February 27, 2002 1:22 PM Subject: Multiple floppies in one system? to etc., on there

Well SOB - they still sell the MCT 8 bit 4 floppy controller - about 1/5th of what it used to cost in 85...here's a link to it: http://www.jdr.com/interact/item.asp?itemno=MCT-FDC-HD4 => -----Original Message----- => From: owner-classiccmp(a)classiccmp.org => [mailto:owner-classiccmp@classiccmp.org]On Behalf Of David C. Jenner => Sent: Wednesday, February 27, 2002 2:22 PM => To: Classic Computer Mailing List => Subject: Multiple floppies in one system? => => => I'm putting together an old 486 system, one of whose main => purposes will be to => read/write floppies of several formats. Like 5.25" 360K, 720K, => 1.2M, RX50, etc., => and 3.5" 720K and 1.44M. I also want to be able to copy RX50s => disk to disk on => the appropriate drive type. => => So I figure it'll take 4 drives (or maybe 3 drives where one is => a 3.5"/5.25" => combo). All of these would be in one enclosure. => => The question is, how to do this without having to unplug/plug => drives every => time you want to make a configuration change? It would be nice => to just be => able to throw a switch or two to re-configure. Not having to => get into the => enclosure would be nice, too. => => I've thought of two ways to do it, but I'm not sure they'll => work, or if there => might not be a better way. => => 1) Plug all the drives into one control cable and switch on/off the power => to the drives to select them. => 2) Plug all the drives into one control cable and select the drives by => switching a control line on the control cable. => => Any comments or suggestions would be appreciated. => => Thanks, => Dave => -- => David C. Jenner => djenner(a)earthlink.net

Jerome Fine replies: I am definitely a PC dummy, so I will not comment on any of the other solutions. However, your mention of the RX50 floppy media leads me to make the following comments. When I did use the RX50 media on my PC in the past (I have not needed to do so for a while), I always felt that it was vital to verify the data AFTER I had done a write. If the file structure is RT-11, you can BINCOM individual files. If not, then in RT-11, you can verify the whole floppy or just individual blocks (from the 800 block total). My suggestion if you are going to copy RX50 floppy media (especially if you are making more than ONE copy) is to do the following.: The E11 hobby version of the emulator is assumed to be in use - "MOUNT DU0: B:/RX50" (a) Copy the floppy to an image on the "hard drive image" COPY/DEVICE/FILES/NOQU DU0: DU0.DSK (b) Verify that the "hard disk image" copy is correct DIFF/BIN DU0: DU0.DSK (c) Copy the "hard disk image" copy to the RX50 copy COPY/DEVICE/FILES/NOQU DU0.DSK DU0: (d) Verify that the new RX50 floppy is correct DIFF/BIN DU0: DU0.DSK In general, you will also find that this takes no additional time (especially if you put the commands in a COM file or type quickly) since the time taken to access the "hard disk image" copy is negligible compared to the floppy access. For example, two COM files could be used, the first with the first two commands and the other with the last two - so you have time to remove and insert a second floppy if you are using only one drive. Over the years, I have not experienced many problems with floppy media, but on the few occasions when the WRITE operation was unsuccessful, a separate READ pass was essential to verify that all of the data had been correctly written. The above COPY/VERIFY approach ensures that. In addition, it takes no more time even with one copy and saves half the time on multiple copies after the first. ======================================== I said I would not comment on the PC, but I do have a question. What drive letters are assigned when there are more than two floppy drives? In addition, if you use just two floppy drives at one time (by safely unplugging both power and the flat cable), then don't you also need to tell the BIOS which floppy drive is being used? Recently, I upgraded to a newer PC. Originally there was JUST a 3 1/2" floppy as the A: drive. BUT when I added the 5 1/4" floppy as the B: drive and even told the BIOS as well, Windows98 would NOT recognize the second B: drive UNTIL I first removed the A: drive. ONLY at that point when the STUPID STUPID Wizard (????) had to look for all the floppy drives did both A: and B: drive become included in the list of drives for the system.