View Full Version : Using 360K disks in a 1.2Meg drive.

March 10th, 2006, 02:16 PM
There is a general misconception that 360K disks, 48TPI, canít be used in a 1.2Meg, 96TPI, drive. They can but there are a few rules that must be followed.

1. A pre-formatted 360K disk (48TPI), one that was formatted in 360K drive, can ONLY be read in a 1.2Meg drive (96TPI). You can NEVER write to this type of disk. Doing so will trash it.

2. You can create a 360K disk in a 1.2Meg drive BUT you MUST first erase the disk with a bulk eraser like those used to erase real-to-real or VHS tapes. After the disk is erased it can be formatted to 360K and the disk can be read and written in a 1.2Meg drive. The disk can also be read in a standard 360K drive. However, you should not write to a disk made in this manor. You can under certain circumstances but as a general rule, donít do it.

In general, disks made in one type of drive are read/write in that same type of drive and read only in the opposite type.

I have been using Teledisk, Winimage, 22disk and other programs for many years without problems. I use Teledisk on a regular basis to create 40 track disks in my 1.2Meg drive for use on my Kaypro 10. Unless the .td0 file is corrupt, and I have found a few, it works every time. I have also used 22disk to move files to and from 40 track disks that were made in a 1.2Meg drive on my PC.

Back in the old days when 40 track 5-1/4 floppies were first introduced, single sided I might add, they were always shipped un-formatted. As the good computers died off and left us with the PC (Pathetic Computer) disk manufacturers started shipping pre-formatted disks. Once a disk has been formatted or written to at 48TPI it canít be written to at 96TPI.


Terry Yager
March 10th, 2006, 02:54 PM

I see you are already aware of the problems associated with trying to write a CP/M disk on a PC with HD drives. I appologize if I assumed ignorance in this matter (in the munged email I sent you). I'm just so used to having to explain the problem to so many folk, it just comes as a knee-jerk these days. Long's you know your way 'round TeleDisk & 22Disk, you should be ok with the archive, if you can convince your mail reader to d/l the file. If not, lemme know, I'll mail you the floppy instead.


Micom 2000
March 10th, 2006, 03:04 PM
Good stuff. Could you expand on the 48tpi/ 96tpi thing. I've forgotten which computers used these formats (blush). I've been trying to make a disk using Putr with my 1.2 fdd and W98 to make a boot disk for a DEC Pro 350 to no avail. I must admit I haven't fired up one of my older Dos boxes and tried that.
I seem to recall that PUTR recommended using a 1.2 fdd.

The usual thing was to format a DEC disks on the DEC Rainbow (which I have). I even have some DEC branded disks. Any thoughts ?


March 10th, 2006, 03:55 PM
I'm not familiar with PUTR so can't give any help there. The 48TPI/96TPI issue is putting a narrow track (96TPI) on top of a wide track (48TPI). The new data in the narrow track has portions of the old data in the wide track on either side of the narrow track. I hope that made sense. Look at it this way.

---------------------------------------- top edge of track at 48TPI
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ top fragment of old data
---------------------------------------- top edge of track at 96TPI
////////////////////////////////////////////// new data
---------------------------------------- bottom edge of track at 96TPI
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ bottom fregment of old data
---------------------------------------- bottom edge of track at 48TPI

You've got a skinny track on top of a fat track. The disk might be readable on a 96TPI drive but will give garbage on a 48TPI drive.

Both teledisk and 22disk are windos hostile! As has been pointed out by others, you must run in pure DOS mode. Windows wants to hog all the I/O and use it as it wants to.