Mike's PCjr Page

Is anyone using a 3.5 inch floppy drive with a PCjr? What kind of drive are you using and what is the density? Is it internal or in an external enclosure? What is required to make one of these work with Jr?

There are two ways to connect a 3.5" drive - direct to the floppy controller and through the parallel port ("Backpack style").

The floppy controller is a double density controller that supports a specific, slower data rate than high density controllers. A genuine 720KB double density 3.5" floppy drive will connect right to the machine's controller; the drive is electrically the same as a 5.25" double density drive except it has 80 tracks instead of 40. If you use a 1.44MB 3.5" drive then things get more complicated because of the differences between double density and high density media, and the lack of a good standard for determining the media type and appropriate data rate.

In short, a HD drive with double density media should "do the right thing" and use the double density data rate. Some older 3.5" HD drives can be jumpered to do only double density data rates, but those are rare now. It's hit and miss depending on the model, so your best bet is to look for a genuine double density 3.5" drive.

If you go with a Backpack drive things are much easier. But also slower, and you can't boot from them as they are a parallel port device.

I use my 3FLOP board to get the extra drives but any extra drive design should work.
and I use ths 3.5 SONY MPF-920-Z drive

Also here is my config.sys

stacks=0<0
files=40
buffers=40
device=jrconfig.sys /v32 /m/b2/d3
device=ansi.sys

note the /d3 is used because I have three floppies running, (2) 3.5" and (1) 5.25"

FYI--The ansi.sys is because I change my screen colors


hope this helps
chuck

That drive looks to be a standard 1.44MB drive. Is there anything special about it?

Your config.sys shows you are set for three drives, but I don't see driver.sys to tell it that the Sony is an 80 track drive. So presumably you are just using it as a 40 track, 360K drive?

I have two and they run as 720K each

Sure, but how are you getting 720K out of them? Are you using DRIVER.SYS, DRVPARM, or some other trick?

I think that later versions of DOS will read the media type from the first sector of the current floppy disk and just use whatever it says is there. But in the case of formatting a diskette you'll need to use options on the format command to specify 80 tracks unless DRIVER.SYS or DRVPARM are used. Without doing something the BIOS and DOS just assume 40 tracks.

Running DOS 5
but I get your thought..

Let me review my setup, been a few months since I turned it on...

seems to read the 720k ok , but did need the
Device=driver.sys /d:1 /f:2

to properly format a blank disk.

could not seem to get the 1.44M format working tho... using the /f:7

Chuckphd53 wrote:seems to read the 720k ok , but did need the
Device=driver.sys /d:1 /f:2

to properly format a blank disk.

could not seem to get the 1.44M format working tho... using the /f:7

It reads 720K because DOS 5 uses the media type byte on the boot sector and ignores the floppy drive type. But you need DRIVER.SYS to tell it how many tracks the drive has if you want to format a blank diskette that doesn't have the media type byte yet.

As for 1.44 - that's not going to work; it requires a higher data rate than the Jr can provide.

Ah .. good, then I am ok... thanks Mike