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some light research


xucaen
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I'm researching the Atari XEGS. I made a list of games on cartridge, and found a list of games on floppy. So then I started looking at available floppy drives for the XEGS. Looks like the XF551 Disk Drive - 5¼" floppy disk (double-density double-sided, 360 KB) was the drive with the highest capacity made (aside from prototypes) for the 8-bit. Now, it's been over a decade since I last used floppy drives (dos/windows) so my memory may be faulty with regards to how floppy drives work. Can the XF551 be used to read any diskette made for Atari 8 bit computers or can it only read double-density double-sided 360 KB diskettes? I'm just wondering what games I could play on it so I can make my lists appropriately.

 

Thanks,

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A stock XF551 is compatible with front side of normal (i.e. 810 and 1050) disks and can't read the back side of those disks.

IIRC, there are mods for this issue, and I believe at least some of the alternative ROMs, can handle back sides of disks.

Also there is the issue, of the density change detection, meaning e.g. if you change from a SD disk to a DD disk, the XF will still try to read a SD disk, which will fail.

It can be made to change density, but that depends on the DOS.

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A stock XF551 is compatible with front side of normal (i.e. 810 and 1050) disks and can't read the back side of those disks.

IIRC, there are mods for this issue, and I believe at least some of the alternative ROMs, can handle back sides of disks.

Also there is the issue, of the density change detection, meaning e.g. if you change from a SD disk to a DD disk, the XF will still try to read a SD disk, which will fail.

It can be made to change density, but that depends on the DOS.

 

Are you sure the XF551 can't read the flip side of a disk? I used to use 'flippys' on a RANA 1000 and I forget the manufacturer of another drive.

I had no problem formatting and using the flip side. Are you saying there is use of the timing hole on the XF551?

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A stock XF551 is compatible with front side of normal (i.e. 810 and 1050) disks and can't read the back side of those disks.

IIRC, there are mods for this issue, and I believe at least some of the alternative ROMs, can handle back sides of disks.

Also there is the issue, of the density change detection, meaning e.g. if you change from a SD disk to a DD disk, the XF will still try to read a SD disk, which will fail.

It can be made to change density, but that depends on the DOS.

 

I seem to recall MS DOS 5.0 did something similar with certain brands of floppy drives. I used to have to remove the disk, try reading the empty drive, then insert new disk. Drove me crazy until I figured out what the problem was (caching of some sort I believe). I wonder if certain versions of DOS for Atari had similar caching issue...

Good to know. thank you!!

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Are you sure the XF551 can't read the flip side of a disk? I used to use 'flippys' on a RANA 1000 and I forget the manufacturer of another drive.

I had no problem formatting and using the flip side. Are you saying there is use of the timing hole on the XF551?

Yes, that's what I'm saying.

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I seem to recall MS DOS 5.0 did something similar with certain brands of floppy drives. I used to have to remove the disk, try reading the empty drive, then insert new disk. Drove me crazy until I figured out what the problem was (caching of some sort I believe). I wonder if certain versions of DOS for Atari had similar caching issue...

Good to know. thank you!!

The problem is not the DOS, the problem is that the drive doesn't reset the density rating if the door gets opened.

If DOS knows, that there can be a problem with XFs (and DOS 2.5 does not, for example), it can reset the density setting on read failures.

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IIRC, the XF used the timing hole for formatting, but not reading. So you can read "flippies" providing they're already formatted.

 

Ok, sorry. I didn't remembered that one correctly. I knew something about timing hole was problematic.

Edited by JoSch
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It actually depends on the drive, or more precisely, depends on which mechanism is inside the drive. Two know mechanism brands are known to be found on the 551:

 

The most common mechanism, at least as sold in the US, is Mitsumi. The Mitsumi mechanism can access the flippy side, just can't format it (well, the controller can't).

 

The Chinon mechanism cannot access the flippy side AT ALL. Not reading, writing, nor formatting. Not without some hardware mode.

 

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I never owned an XF551, 1050's with a DD upgrade and making "flippy" disks for a full 360K per disk was fine for me. But I remember reading Bob's CSS ads about his XF551 upgrades back in the day, like for installing a 3.5" or having both 5.25 and 3.5 dual drive, etc. but the ads, IIRC, also said that the way the XF551's were designed was that they write to the back side of the disk backwards, which was what created incompatibility issues, and that his upgrades would fix that issue too.

Edited by Gunstar
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