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8 inch disks

My home made system is a 8080A, with 64K of memory. I have a 2k EPROM(62-64K) editor that I wrote 40 years ago that allows me to crudely work. Recently I added serial port to my IBM XT so that I can save programs on 5 1/4" floppies of the XT. I have always wanted to connect the 8" drives directly to my 8080. I have wired up a 8272 chip and last winter I installed a 8237 DMA chip. I had some trouble with the DMA, due to wiring errors, but have gotten that straightened out. The DMA works like it should. I have two 8" drives a Shugart and a Siemens. The Shugart works fine, as tested with Dave Dunfields program. So I'm sure that the drive will work with the 8272. My plan is to recheck and re-familiarize myself with the 8272 documentation and my wiring. Then I thought of writing a few test programs. I figure that the 8272 needs to be first initialized with a SPECIFY command. I've found the drive parameters for the head load and other times. The program would poll the 8272 Main Status Register and then output the specify command followed by the time parameters. Once that is done I thought I'd try a Sense Drive Status command and maybe a recalibrate command. Once I figure out how those commands work, then I'll look at a read routine. With this under my belt I figure that I can make Cold Start Load program, that I can add to my editor space. So.... maybe this winter I ll progress a little farther toward the goal of getting CP/M to work on this system. Thanks for the help, Mike.
 
I picked up a couple of 8" floppies at a garage sale. They show some read errors on the tracks 70 and higher. Can I use these disks and just avoid the upper tracks? Thanks Mike
 
My guess is that they might last a bit, but eventually, they'll start shedding like someone's Angora cat and foul the heads up on your drive.

For what it's worth, depending on your drive, you might even get by with hard-sectored media, if that's cheaper.
 
Mike_Z said:
...picked up a couple of 8" floppies...read errors on the tracks 70 and higher
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You can block out areas of the floppy by a directory hack, CP/M really doesn't address it well. You'd need to write a director entry that reserves the BLOCKS (group of N sectors) containing all the bad sector/tracks. Call the file SECTORS.BAD or such and don't delete it. You might want to write a CP/M system disk command file to allow you to orchestrate that.

I inspect suspect 8 inch floppies before using. The hub condition seems to be a good clue indicator at least for this dry region. I inspect the magnetic media by putting three fingers in the hole at the hub and expanding them to prevent the magnetic media from turning. Next I turn the jacket to view the magnetic media through the access slot as the jacket rotates around the full revolution. For double sided floppies just flip and do the other side inspection likewise.

As this requires no tools and does no harm if done right, you can inspect the media at garage sales before deciding to purchase. Down here in Texas we have less catastrophic media failures than in coastal regions; so the most we see here is head-wear shown as the concentric tracks of varying intensity on the media.
 
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Price was not even a consideration. I got 5 of them for a dollar. One would not work at all. Two showed lots of errors but the last two only had errors and not many on tracks 70 and above. Once I get the machine working I can give it a try, nothing to lose. Mike
 
I don't know what environment these disk lived in, but I try to keep the disks in sleeves and that in boxes. The temperature and humidity are what ever it is in the house, rather warm and dry. I clean the heads with a q-tip and alcohol, I watch them periodically. No smoking in this house, the boss (wife) won't allow it. I've been looking for replacement belts. The belt in my Siemens is bad. I picked up a junk Siemens drive that has a belt, but missing other parts. Will try that belt and the boiling idea. I'm hoping that the pulleys are just slick, but who knows. Mike
 
The other trick with a stretched belt is to kludge in a re-tension pulley; a pulley outside a straight-line belt path, to put in a new belt corner making the total distance longer. Frankly I'm surprised some vintage hobbyist just doesn't make a standard part to do that.

I wondered if there were chemicals used in gasket coatings that would revitalize the belt - so contacted an inventor that is good for information like that. He says he knows of an anti-slip chemical that makes the belt more sticky - hence anti-slip. He's used them in automation equipment - so that may or may not have the characteristics that would apply to floppy belt use.
 
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Boiling for a slightly loose belt very often works. I've done it with success.

If the belt is getting dry and losing flexibility, soaking in a solution of wintergreen oil and a solvent (say, xylene) will often soften it up (used a lot on typewriter platens and motorcycle parts). You can find wintergreen oil (methyl salicylate) mixtures sold as a tire dressing. In any case, it smells nice.

Belt dressings can be purchased at the auto supply store, but are often more trouble than they're worth. If the belt slips because it becomes too large with drying out, dressing isn't going to save you--you'll just end up with a gummy mess.
 
Chuck(G) said:
....(snip)....
But most early disk controllers could not set up for another read transfer in the "gap" space between sectors, so trying to access sectors consecutively would result in a loss of one revolution for each sector read. That is, instead of reading up to 26 sectors per revolution, it would take 26 revolutions to read all sectors on a track.
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This may be a little off-topic, but the Western Digital 179x controllers didn't exactly 'read sector' the way the uP765 did/does.

These could read the entire TRACK at once (formatting, inter-sector stuff, etc), meaning if you for example wanted to use some bank-switched memory, you could read a whole disk in a couple seconds making disk-to-disk copies MUCH faster. And if you wanted actual files, you could de-interleave them by setting your 'read sector deblocking' for whatever had been used to write them.

You might look into what Mountain disk copiers used for softwares, as they (among others) made disk duplicators that were much faster than usual PC speeds. I seem to recall seeing 360k disks chunking out in maybe 3-4 seconds apiece..... may have been copying less than forty tracks, though.

Of course, they probably used TWO heads, for continuous read-after-write to spot errors ....

Bill
 
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