Trying to boot from a stock IBM 4869 on an 8088 clone or IBM 5160 - Is it possible?

[RJBJR]

I have a working IBM 4869 with a DSDD drive, it functions properly and is accessible via DOS on the system I'm using as a test bed for cards and peripherals. It has the stock drive in the enclosure. Is there a floppy controller that I can use to have this drive recognized as the A: drive during boot? It would probably have a user configurable switch that could toggle between the 34-pin internal and 37-pin external cable connector on the card to allow the external device to boot.

The reason I'm asking is I have a bunch of hardware to go through and having this drive bootable would simplify things a bit. Thanks for any help.

 

[aoresteen]

The orginal IBM floppy controller for the 5150 had a 37 pin connector on it. I *think* it will boot IF there are no other drives connected. HAve you tried it as the only drive?

 

[RJBJR]

The orginal IBM floppy controller for the 5150 had a 37 pin connector on it. I *think* it will boot IF there are no other drives connected. HAve you tried it as the only drive?

Thanks for the reply.
Yes, tried it by itself with three different brands of cards. It always comes up as c: or d: (and e: with a HDD)depending on how the switch is set on the back of the floppy drive in the 4869.

The 4869 will only show up if the motherboard switch settings are set to either 3 or 4 floppy drives, it doesn't show when the motherboard switch settings are set to either 1 or 2 floppy drives.

With a HDD the 4869 gets assigned as d: or e:. This 4869 has yet to be assigned as b: or a: from the 37-pin external port.

I can plug a regular 5.25 DSDD drive into the internal floppy connector and it boots while the 4869 remains assigned to what it was. Tried the 4869 by itself, with an HDD, and with the second floppy installed to the internal floppy connector. The only thing that will make the drive change drive letter is when the HDD is installed, then the floppy changed downstream to the next available letter.

 

[MikeS]

If you're up for a little tinkering, as far as I can see all you would have to do is invert the signal at U17 pin 5; looks like there's a spare section in U29 that you could use. It would involve cutting the trace from U17-5 to the via going to the rest of the circuit and running jumpers from U17-5 to U29-11&12, and from U29-13 back to the via.

You could even add a switch to select between normal (1 & 2 internal, 3 & 4 external) and flipped (1 & 2 external, 3 & 4 internal).

Of course I'm just looking at the schematic and the adapter and assume no responsibility whatsoever!

I await Chuck (G)'s comments ;-) Maybe there's even a way to do it without hardware mods.

 

[JohnElliott]

It might be simpler to introduce a 37-way plug and socket into the internal floppy ribbon cable:

Controller----------------< <------------------Internal drive

and bring the plug and socket out of the case (probably through one of the ISA slots). Then you can swap the internal and external drives over just by swapping the plugs.

 

[MikeS]

It might be simpler to introduce a 37-way plug and socket into the internal floppy ribbon cable:

Controller----------------< <------------------Internal drive

and bring the plug and socket out of the case (probably through one of the ISA slots). Then you can swap the internal and external drives over just by swapping the plugs.

Well, I'm not sure it's easier to find and buy the connectors and make the cable, and a switch would be more convenient than opening the case to swap cables, but it's certainly an option, especially if the idea of cutting a trace on the FDC bothers you.

 

[RJBJR]

It might be simpler to introduce a 37-way plug and socket into the internal floppy ribbon cable:

Controller----------------< <------------------Internal drive

and bring the plug and socket out of the case (probably through one of the ISA slots). Then you can swap the internal and external drives over just by swapping the plugs.

Well, I'm not sure it's easier to find and buy the connectors and make the cable, and a switch would be more convenient than opening the case to swap cables, but it's certainly an option, especially if the idea of cutting a trace on the FDC bothers you.

FWIW, I was just considering a way to use the drive in the 4869 enclosure as the boot drive because it's protected and I could spill my coffee on it and use it as a table <g> but it's ~almost just as convenient to just string a long cable from the internal connector to a free standing drive, I guess that is what I'll do. Going to just use it for running through floppy drives and motherboards to see if they still work.