motteler@umbc4.umbc.edu (Howard E. Motteler) (03/03/91)
A while back, Michael G. Beirne writes: > I use a Mitsubishi 5 1/4 inch 1.2 meg floppy jumpered to fix the > disk speed and this gives me a 720K 5 1/4 floppy. This way I can > just reformat my old 360K backup floppies and use them again. Is this the same (or similar to) as the "quad-density" from way back in the CP/M days? I'd be interested in trying this. How reliable are the 5 1/4's used this way? Would it be possible (e.g., with an external switch) to toggle the drive between regular and half speeds, and read both sorts of disks? >Send me mail if you want the jumper >list for the Mitsubishi drive and an "iv" description file. Please post this (or mail me the info!) I suspect a number of people might want to try it. Howard E. Motteler | Dept. of Computer Science motteler@umbc3.umbc.edu | UMBC, Catonsville, MD 21228
floyd@ims.alaska.edu (Floyd Davidson) (03/03/91)
In article <5238@umbc3.UMBC.EDU> motteler@umbc4.umbc.edu (Howard E. Motteler) writes: >A while back, Michael G. Beirne writes: >> I use a Mitsubishi 5 1/4 inch 1.2 meg floppy jumpered to fix the >> disk speed and this gives me a 720K 5 1/4 floppy. This way I can >> just reformat my old 360K backup floppies and use them again. > >Is this the same (or similar to) as the "quad-density" from way >back in the CP/M days? > >I'd be interested in trying this. How reliable are the 5 1/4's >used this way? Would it be possible (e.g., with an external >switch) to toggle the drive between regular and half speeds, and >read both sorts of disks? > Yes to all of the above, and more. I have both the original 48 tpi drive, and a 96 tpi drive mounted in an external case (along with an external second hard drive). The data cable is daisy chained to both drives, both are set up to be the first drive, and only the last one has the terminating resistor pack plugged in. On the data cable coming from the motherboard cut the drive select line (I think that is pin 10, but you need to check it out), and put a single pole double throw switch in. The pole goes to the line from the motherboard and the two sides of the switch go to either disk drive. The switch then selects which drive is used. I have not used 3.5" drives, but others have with the same results. With the 5.25" drives it is also possible to get a little more space than is specified (I don't know how this works on 3.5" drives, it may not). To use the 96 tpi drive you need to change the description file in /usr/lib/iv to have 80 tracks instead of 40. That is were a little diddling can change things. Use 84 instead of 80. And on 48 tpi disks (for the original drive) use 42 instead of 40. If you try more than 84 on a Teac 55F it will bang the stops on the head mechanism. If you try 44 with the original drive (mine is a Teac 55B) it will format just fine, and you can even write to it, but... when you read back a cpio archive it can't read the disk! So stick with 84 on a 96 tpi drive and 42 on a 48 tpi drive. Or if you have other than Teac drives, try it and see if they are different. The capacity for 96 tpi drives is 835k for cpio (819k for a file system). For a 48 tpi drive it is 395k and 386k, respectively. The description file used is /usr/lib/iv/FD10nl, with the number of cylinders changed as appropriate. A set of several description files, described as for use with 3.5" drives, was posted a long time ago, and is on osu-cis, I think. It has been very reliable for me. I've been using 96 tpi drives for years with plain old 1D disks (thats right, single sided disks. The cheap ones too!) I've got disks that are 6 years old that are readable (on a Kaypro, not on a UnixPc...). And it hasn't hurt the drives either, as I've been moving the drives from one computer to another as the old computers byte the dust. Actually I have 6 Teac 55F's that date back to 84-85 and have not had any of them fail (unlike the Tandon's I had...). The only problem is that if you just one time write on a disk with a 48 tpi drive, it has to be bulk erased to use it on a 96 tpi drive. The narrower track that a 96 tpi drive writes on the disk will be right down the middle of the 48 tpi track and even a small mis-alignment of the head will read part of the 48 tpi track and cause errors. I bulk erase with two very large speaker magnets (4" in diameter each). Anything less will erase the data well enough that you can't read it, but will leave enough to cause problems. I was actually amazed at what it takes to really clean off a disk! Floyd -- Floyd L. Davidson | floyd@ims.alaska.edu | Alascom, Inc. pays me Salcha, AK 99714 | Univ. of Alaska | but not for opinions.