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IBM 5150 3.5” formatting at 360K

Mochatea396

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Hello group,
I’m in the process of fine tuning an IBM 5150. The hardware is “as is” from when I took possession of it some 30 years ago. It has one 5.25 floppy, a seagate hard drive (which is the boot drive) and a 3.5” floppy drive. It’s O/S is DOS 5.0. Both floppy drives format blanks without errors but the 3.5” only formats to 360K. Says it on the screen before it starts formatting the disk. Is this a setting that someone set somewhere? The person had the video switches set to 40 column as well and I set them for 80. (No idea why someone would do that). But that got me wondering if he has this drive set to 360K somehow. I’ve attached a photo of my drive cards (top card is the 3.5” card). I see a jumper on the upper left, could this being jumped be causing it? Just an thought.
Any input would be appreciated. I’m just getting into vintage IBMs and I’m still new at them.
Thanks
 

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The 5150 has no BIOS concept of anything other than 40 track 5.25” drives. If you have a 3.5” drive installed it can read it just fine, because DOS will look at the disk itself and use the geometry it was formatted with, but as you’ve noticed, it‘ll fall back to the BIOS when formatting a blank disk.

Easy fix is add the following line to config.sys on your boot disk:

device=c:\dos\driver.sys /d:1 /f:2

this overrides the BIOS supplied geometry. Change the /d to “0” if the 3.5” is drive A instead of drive B.
 
Lots of IBM 5150 information at minuszerodegrees.net

You will notice that the previous two posts concern 720K sized 3.5" diskettes, rather than 1.44M sized diskettes. That is because the floppy controller you are using does not support High Density. If you are seeking the use of 1.44M diskettes in your 1.44M drive, see the '1.44M diskette in 1.44M drive' section at [here].
 
Thanks everyone. I looked at minuszeros website and offers options. I did locate the DRIVER.SYS file in DOS. I'm not looking to use 1.44 disks, just 720K. Looks like I need to add a line to the config.sys file. I'm having trouble doing that. (I mentioned I'm new to IBMs). I open the config.sys file with edit, but everything I've tried to add a line doesn't seem to let me. DEVICE=C:\DOS\DRIVER.SYS /D:1 /F:2. Looks like what I need to add since my 3.5" is in location B.
Thanks everyone for you responses.
 
*sound of forehead slap*

Instead of Driver.sys a better option under most circumstances is DRIVPARM. It likewise goes in config.sys and has similar syntax, but it has advantages in not causing drive letter weirdness.


The one caveat is DRIVPARM wasn’t supported in some OEM versions of DOS, notably IBM PC-DOS prior to 5. But if you’re running DOS 5 it should be fine.
 
Thank you all for your help.....and your patience. I was able to enter the line from minuszeros website into the config.sys and on reboot it all appears to be working properly.
Thanks again group
 

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Im going to agree with Eudimorphodon that you dont want D: as your floppy drive letter. Especially your primary floppy. Your going to have problems with software. This is a good start but you should do the DRIVPARM route so you can get a conventional drive letter for compatibility.
 
*sound of forehead slap*

Instead of Driver.sys a better option under most circumstances is DRIVPARM. It likewise goes in config.sys and has similar syntax, but it has advantages in not causing drive letter weirdness.


The one caveat is DRIVPARM wasn’t supported in some OEM versions of DOS, notably IBM PC-DOS prior to 5. But if you’re running DOS 5 it should be fine.
DRIVPARM works in PC-DOS starting with version 3.2
 
DRIVPARM works in PC-DOS starting with version 3.2
Are you positive? I could swear it was a thing that it worked in, say, Compaq DOS 3.31 and Commodore DOS 3.2, but IBM 3.30 was a no go.

Related info:

1. Post #6 at [here].

2. From [here] is:
On Sun, 4 Oct 2020, Chuck Guzis via cctalk wrote:
> IIRC, in xDOS 3.2 and 3.3 DRIVPARM produced an error if specified as
> usual, but when DRIVPARM was suffixed by a string of three contorl-A
> (hex 01h) characters, it worked fine.
 
Another option is to run SETBPB35 from AUTOEXEC.BAT or the command prompt:

ftp://ftp.oldskool.org/pub/tvdog/tandy1000/misc/setbpb.zip

This program will set the device characteristics for the A or the B diskette drive to indicate that it is a 720K drive instead of a 360K drive. It requires DOS 3.2 or later and does not take up any RAM.

The only command line parameter is the drive letter (A or B).

For example, to indicate that your B drive is a 720K 3.5" diskette drive:

SETBPB35 B
 
Related info:

1. Post #6 at [here].

2. From [here] is:
On Sun, 4 Oct 2020, Chuck Guzis via cctalk wrote:
> IIRC, in xDOS 3.2 and 3.3 DRIVPARM produced an error if specified as
> usual, but when DRIVPARM was suffixed by a string of three contorl-A
> (hex 01h) characters, it worked fine.
I'm positive that I've been able to make it work for me in both PC-DOS 3.2 and 3.3. I didn't have to use those 01h characters either, however I did notice that the system would get very picky about the content and ordering of the config.sys file and sometimes produce errors for seemingly no reason.
 
I see a jumper on the upper left, could this being jumped be causing it? Just an thought.
I cant tell if this is the original IBM floppy controller or a clone, either way it looks to be the original. Does this jumper have something to do with the twist in the cabe due to where it is?
 
I cant tell if this is the original IBM floppy controller or a clone, either way it looks to be the original. Does this jumper have something to do with the twist in the cabe due to where it is?
The card looks like the revised IBM controller. Tried to follow the traces but the jumper that remains is connected on the reverse side and I am not sure what components are at the end of each trace.
 
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FWIW, it’s not my imagination, DRIVPARM was a documented command in Commodore DOS 3.2. Page 251 of the Commodore DOS manual. (319 of this combo PDF.)


Searching this PC-DOS 3.30 manual nets no hits.


I used to chuck 3.5” drives into surplus 5150/60’s back in the early 1990’s (set them up as word processors for charity cases) and also happened to have a boxed copy of real IBM 3.30 that I distinctly remember not using because it didn’t support DRIVPARM, I guess it would have been useful to know at the time that spewing some control characters into CONFIG.SYS could fix that.
 
Some OEMs did make DRIVPARM available in MS-DOS 3.2 and 3.3 to support their unique configurations. But in plain-vanilla MS-DOS, it was not officially documented or supported until MS-DOS 3.30A.

Tandy went even further and added support for 3.5" 720K drives into their version of MS-DOS 2.11 for the 1000HX and 1000EX, even though regular MS- and PC DOS didn't support 3.5" drives until version 3.2.
 
Version 2.11 has 720KB support? I used alot of DOS 2.10... Never 2.11. I take it, it was a Tandy specific release? I have a Tandy 1000HX that I should try that in.
 
Version 2.11 has 720KB support? I used alot of DOS 2.10... Never 2.11. I take it, it was a Tandy specific release? I have a Tandy 1000HX that I should try that in.
Yes, it was Tandy-specific. If you have a 1000HX, you already have it in ROM!
 
MS-DOS 2.11 with 3.5" support was available from a number of vendors including Tandy, Toshiba, and Kaypro.

The first IBM release with 3.5" 720K support was PC-DOS 2.1 for the JX.
 
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