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TRS-80 Model 4P - disk mod possible?

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commodorejohn

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So I'm considering getting a Model 4P as the CP/M machine I was looking for in another thread. 64KB RAM and 4MHz are definitely within what I'd be looking for, and as far as luggables go it looks like a nice machine. Only problem is that the disks are single-sided and hold 180KB, and...well, that's just claustrophobia-inducing, especially so since apparently making "flippy" disks on the TRS-80 involves cutting another index hole in the disk jacket!

I noticed while looking at some of the other Model 4 specs that there was a Model 4D which used double-sided disk drives for 360KB disks - not vast and capacious, but a darn sight better than 180KB. So my question is: would it be possible to install double-sided disk drives in the Model 4P with some reasonable amount of effort? Is it as simple as replacing the drive mechanisms, or do the 4P and 4D use different disk controllers? And would that require a ROM replacement?
 
If you want to use 3.5 drives you will need to make a cable...

The image supplied works GREAT... I know, I built/use it! :D

Cable Diagram FDD.jpg
 
Or find drives that allow you to change drive select and I think a straight through cable would work. Of course, it's getting tough to find 3.5" drives that allow you to change drive select.

Another tip: If you're going to use a 1.44 mb drive as 720k is to either disable the HD sense circuit, make sure you always use DS/DD media or to make sure you cover the hole in the HD media. I've had problems using an HD drive and HD media in a machine that only supports DD.
 
That IS true... at first I used tape to cover the 1.44 hole... THEN I modified the drive so I wouldnt need to...

I doubt finding a drive that would allow a straight thru cable... but Im sure they DO exist... :roll:
 
Attempting to disassemble the 4P to change the drives is fairly straightforward. If you're planning on running CP/M, you may want to consider increasing your ram to 128K as I have with mine. You'll find it much faster and easier to use.
 
Sorry to bring this thread out from the past, but it is definitely relevant in my quest for knowledge, and education. This is just what I’m looking for. So please accept my quest for information. It is my hope that your answers will help me get the most out of my TRS-80 Model 4.

So, above all of the confusing info, can I install 360Kb floppy discs into my TRS-80 Model 4? And, to take to another level, can I use the full 360Kb discs?

The reason ask is that I don’t have the knowledge needed to create single sided floppies. And since the computer has 2 - 5.25” discs installed and both drives are only 180Kb single sided drives, I would love to swap out these floppy disc drives, in favor of the 360Kb double sided ones if possible.

So, what is the consensus regarding swapping the TRS-80 Model 4’s floppy drives out in favor of the 360Kb drives? Will I be able to use the full 360Kb, or is there another option I’m missing?

As always, thank you very much.

Thomas
 
bettablue said:
"The reason ask is that I don’t have the knowledge needed to create single sided floppies."

You can use 5.25 DSDD disks with the TRS-80 M4 Single-Sided Drive. It just uses one side,
I don't think I ever used single-sided disks on my M3/M4, except when I first purchased the Model 3.
All Radio Shack's disks at the time were SSSD.
Later I found that the 360k DSDD disks I purchased in bulk for my MSDos PC also worked on the Model 3.

Of course, you can swap out the 180k drives with 360k drives if you need the extra space.
But you don't have to do this just to use 360k DSDD disks.
 
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Whatever method you use to create the disks, the images out there are already in the single sided format except for the rare double sided images like Deskmate.

Replacing working drives is an option but today its a crap shoot to get working, aligned full height double density drives that look right in the machine. Without the equipment you'll never really know if it works or what needs to be done to bring it back to alignment. I'd say if you go the route of the FreHD or M3SE you don't need double sided drives and if you are using tools in the IBM to create the disks, those tools should be reading images with side information in them and work fine.

Under LDOS you have to answer sides when formatting, under the other DOSs that do support double sided disks, you have to configure them to do so in the OS. TRSDOS 1.3 doesn't even support it without extensive patching and even then its not really ideal. Bottom line is until the very last Model 4 (the 4D) everything out there assumed single sided drives and double sided was an exception.

I'd stick with 180K single sided drives, you'll not benefit from it very often with a hard drive emulator (or even a hard drive).
 
The Model 4 will handle double sided drives. You might need to make a new drive cable; I don't recall if the Model 4 used the "missing pins" method for drive select. My Model 4Ps do, so the 4 probably does, too. I have a 4P with 2 3.5" DSDD 720K drives and a 4P with 2 5.25" DSDD 360K drives. Except TRSDOS for the Model III, all support the larger capacity drives.

I play with too many DOS types to use a hard drive or emulator. The larger floppies suffice for me. As Tibs pointed out, you don't NEED DSDD drives. It depends on what you want to do with the computer.
 
lafos said:
The Model 4 will handle double sided drives. You might need to make a new drive cable; I don't recall if the Model 4 used the "missing pins" method for drive select. My Model 4Ps do, so the 4 probably does, too. I have a 4P with 2 3.5" DSDD 720K drives and a 4P with 2 5.25" DSDD 360K drives. Except TRSDOS for the Model III, all support the larger capacity drives.

I play with too many DOS types to use a hard drive or emulator. The larger floppies suffice for me. As Tibs pointed out, you don't NEED DSDD drives. It depends on what you want to do with the computer.
Click to expand...

Yes, the Model 4 like the Model 4P does use a cable with missing pins. The Model 4D cable doesn't have any missing pins.
 
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