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Compatability between Drives

8

8008guy

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Salt Lake City, Utah
I have a CPM machine running with two floppy drives on it currently. A teac FD-55GFR and a Tandon TM100 2A. I have the Teac strapped to run at 300RPM. Each drive can read and write its own floppies just fine. The disks can only be read from the drive they were written in.

Question... Might this be an alignment issue? Or is possible that the drives read/write head widths make them incompatible?

len
 
Correct. The software would have to know to double-step the 96TPI drives head to even be vaguely compatible (but then there are other compatiblity issues writing 48tpi disks in a 96tpi drive). Since we are talking about CP/M, I'm assuming this is not happening here.

What type of machine is this?

If the OS uses a 40 track format, then you really want another 40 track (48TPI) floppy 5.25" drive.

If this system also knows how to fully make use of 80 track formats, then the 96tpi drive would be able to store more data on the disk. But the disks will never be readable by a 48TPI drive since the head only steps half the distance.
 
Hi SomeGuy,

It's an 8080 bench system. I modified the CBIOS, there is no double step support. I'll just pick up one or the other dives to have a pair of the same and all will be good.

CHeers,

len
 
Depending on the program you use to format disks, you can tell the 96tpi drive format the disk to be 48tpi and thus allow for reading on the 48TPI drive. It may be that the 96tpi drive is already formatting as a 48TPI drive because your system does not have a 96TPI option. If this is the case, then yes maybe you have an alignment problem with one or both.
b
 
I think there's some confusion here:

Unless the controller knows how to double-step (unlikely in a CP/M system) formatting a disk as 48TPI in a 96TPI drive will not give you a 48TPI disk; instead, it will give you a 96TPI disk with only the first 40 tracks used, completely incompatible with any 48TPI drive.

m
 
Exactly. I think Bill may have the CP/M CBIOS confused with what the PC BIOS does.

FWIW, I used a 96 tpi Micropolis DSDD B: drive in my 5150 back in the day. But that had no compatibility with the 48 tpi SA450 A: drive already in there. But it was a floppy-only system and getting 800K ( I used my own routines for 10x512 sectoring) on a floppy was very convenient.

The 5170 brought in double-stepping on the 1.2MB drive as a way to handle older legacy 160/180/320/360K disks. That one was a puzzler, BTW. IBM could certainly have offered DSDD 720K option for the 1.2MB drive in addition to being able to read 48 tpi 360K disks, but for some odd reason they didn't. Such a move would have made transitioning to 3.5" DD media much simpler (identical logical format).
 
In the mean time I may pull a TM100 out of idle 5150. The TANDON sounds cooler than the TEAC. :)

It's tough, about 3/4 of the old drives I buy on ebay are junk. For anything that looks clean they want an arm and a leg. If anyone has a reasonably priced TM100-2A pm me.

I do have two Magnetic Peripherals 5.25 inch drives that I'd trade for. Once of them has a messed up head, otherwise they are reasonably clean.


len
 
Depends on how much you want to put on a disk. The Teac GF can hold (at DD rates) twice what the Tandon will--and, if you have a capable controller, it can also emulate an 8" drive if run at 360 RPM.

Tandons, in my experience are mostly shoddy merchandise, adopted because they were less expensive than other brands. As far as reliability and construction, they don't hold a candle to most Teac dives.

BTW, The suffix on Teac drives indicates the density support as well some other interesting aspects, (e.g. R = right-side release lever). The -B and -A drives are 48tpi. -F is 96 tpi 300 RPM DD, -G is 96 tpi 360 RPM HD, -H is 3.5" high density (135 tpi HD). So, an FD-55-GFR is 5.25", supports both 720K and 1.2M and has a right-side release lever. A FD235HG is a 3.5" drive that support 720K, 1.3M and 1.44M (3-mode drive).

And so on...
 
Yep, I can certainly go the TEAC route. I just have a really nice full height cabinet that is more period correct. For my Altair I just two TEAC's in a homemade wood cabinet.

I mainly build this stuff to play with. I am more interested in functionality than visual perfection.
 
So why not 4 drives? Many controllers of the period could handle them.

Or even a couple of emulators and 2 drives?

That would be very functional.
 
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