View Full Version : Trouble using 3 1/2 on IBM-5150

Retro Canada
September 21st, 2017, 09:26 AM
Hi, I have a 5150 but I have no means to transfer a disk image to the 5 1/4 so I tried using a 3 1/2 disk. For imaging from an Windows 10 I use an USB 3 1/2 (pulled from Dell laptops) that truly works with 720K disks as I used it for MSX disks before. I used real DS/DD 720K disks, formating with format /T:80 /N:9, and transfered using winimage. The generated disks are perfect readable on MSX machines which does 720K ms-dos compatible.

But the IBM5150 will turn the light on , spin a little and but completely ignore it in the boot. It's a BIOS-3. Interestingly if I leave a blank disk on 5 1/4 it will complain about not-bootable disk when using the 3 1/2 it is just silent about it.

I have 3x 3 1/2 drives: 2 x 1.44Mb (DS0 and DS1) and a truly DSDD 720K with jumpers for the DS. I tried as DS0, (as my cable is not twisted). I used them in other computer with no trouble: color computer 3, MSX, etc. Only this 5150 is ignoring them.

So what could be wrong ? The switch 1 has the dip 1 to OFF: one or more floppies. Is there any other setting or jumper to set ? None of the 3 working floppies worked. Again I tried with real DSDD disks and HD disks with HD hole taped.


September 21st, 2017, 10:40 AM
A straight cable gives you drive B: with DS1. The cable "twist" is necessary, as it not only swaps the drive select output, but also the motor enable output to give you a drive A:. Otherwise, if you set a drive to DS0 with a straight cable, you'll get drive select (i.e. the LED will go on), but the motor will not be activated.

Retro Canada
September 21st, 2017, 10:46 AM
Ok I will try using a twisted cable (in fact I need to add an IDC-34 to my cable). This seems to be the difference between other platforms as they do have multiple motor lines.

Retro Canada
September 22nd, 2017, 06:03 AM
And it worked :)

This machine came with a 150W PSU (leadman pc-130a), a WD1002S-WX2 controller and 2 HDD: a ST-225 (20MB) and a HH-612 (10MB). I was able to low level format the ST-225 to 20MB after changing the jumpers on the board (it was set to 10MB). My question is can I use mixed sizes in this same controller or I will have to use the same geometry and loose 10MB on the ST-225 ? Does it store the geometry in the drive once formatted or always use the one set in the jumpers ?