XF551 with CSS Enhancer

[+Larry]

Here is the third of the modified XF551 drives.  The Enhancer is an update/fix for the XF551 which made it backward compatible with the 1050, etc.  The main problem that it solved was that you could not format to the back of a disk on the XF.  I've also read that on some European models, you could not even write to the back side. (?)  Aside from fixing some minor issues, this update does not add UltraSpeed.  In 1050 mode you are limited to 1X SIO.  If you format in XF551 mode in DD, then you can get 2X SIO. 

 

Here are some pics (nothing really striking -- just a very small toggle switch on the back of the drive). The label is a Brother P-Touch label (love 'em!) to show which toggle position is which. There is light yellowing on this one. It has spent most of its life in a box, but still would benefit from retrobrite.

 

I've got to check how many more XF's I have.  A couple more stock ones, I think. My best story about an XF551 is one I got from eBay.  The seller put the drive in a plastic shopping bag and then put it in a pretty large box with zero padding.  Needless to say, the mech was "whacked" when I got it. But I ended up paying about $30 for that one, and the pcb and case were still good, so ended not so bad.

 

-Larry 

 

 

 

 

[+Larry]

There is a nice write up of the XF551 at Atarimania:

 

http://www.atarimania.com/faq-atari-400-800-xl-xe-what-is-the-atari-xf551-disk-drive_29.html

[Mathy]

Hello Larry

 

7 hours ago, Larry said:

The main problem that it solved was that you could not format to the back of a disk on the XF. 

 

The "problem" was that you couldn't format the backside of the disk as a single density disk.  The XF551 supports double density, so the backside can be formatted, but only when the complete disk was formatted as a double sided disk.  For storing data, using double sided disks was better, since you can get more data one big disk than on two small disks.  It became a "problem" when people used software that either didn't support anything bigger than a 1050 can handle or that depended on the disk being single or enhanced density.

 

Sincerely

 

Mathy

[+Stephen]

5 minutes ago, Mathy said:

Hello Larry

 

 

The "problem" was that you couldn't format the backside of the disk as a single density disk.  The XF551 supports double density, so the backside can be formatted, but only when the complete disk was formatted as a double sided disk.  For storing data, using double sided disks was better, since you can get more data one big disk than on two small disks.  It became a "problem" when people used software that either didn't support anything bigger than a 1050 can handle or that depended on the disk being single or enhanced density.

 

Sincerely

 

Mathy

Didn't it also write data on the backside "backwards" - meaning it couldn't just be flipped over in a single sided drive like 1050 (even if 1050 was capable of reading a double density disk)?

[+CharlieChaplin]

54 minutes ago, Stephen said:

Didn't it also write data on the backside "backwards" - meaning it couldn't just be flipped over in a single sided drive like 1050 (even if 1050 was capable of reading a double density disk)?

 

The disk is "spinning in the other direction" (the second read/write head writes data the other way around, i.e. if one side is written clockwise, the other side is written counter-clockwise) and because of that a 1050 (even when enhanced!) can only read the first half of a DS/DD diskette.

 

Sidenote: Not sure about the 810, can it read the first 720 sectors of a 130k disk or is it unable to do that ? If it can't read a 130k disk at all, then I am wondering why Atari DOS 2.5 used the < and > brackets for 130k disks with files beyond sector 720...?

 

If you format the backside of a diskette with one index hole on the 810 or 1050, then the Mistumi XF551 can at least read it or write to it (it just cannot format it). The later Chinon drive mechanics are worse, they cannot read, nor write nor format this backside, since they always look for the index hole...

 

 

[+Larry]

Exactly. You could not flip the disk and format side B as with any typical SS drive because of lack of a second timing hole opening on the jacket.  And I would say that was a problem.  But I and probably quite a few others did make a template to punch a new opening in the jacket sides -- homemade flippy.

 

@Stephen- 

Yes, plus other things.  Since the disk was not flipped when using 360K mode, most everything was "fubar" on a SS drive. Sector numbers incorrect, no VTOC/directory on side B, and sectors written in reverse order. 

 

Charlie Chaplin beat me!

 

[_The Doctor__]

punch an index hole in the jacket only, same as write protect wheres the problem?

 

You can build an index hole faker or even an index hole doubler...

 

last I knew there was still one guy showing the fixes on the web somewhere.

Edited June 10, 2020 by _The Doctor__

[+Larry]

Sure you could. The homemade flippy was not difficult, but making a bunch was tedious.  Buying flippies back then was fairly expensive.  And the "faker" would be beyond the capabilities of many users in 1988.  Arguably still is. I think Floppydoc published a mod for this. Anyway, Puff's solution, like most everything he did, works really well. Flip a toggle switch 1050 <--> XF551.

[+Stephen]

Dumb question - how do you punch an extra hole in the disk jacket without also punching through the inner disk, thereby ruining the indexing?  I notched all the write protect tabs on my disks, but the disk was not in that area.  Did you have to remove the disk from the jacket, punch the extra index hole, then put the disk back in?

[StickJock]

I never punched the index hole on 5.25" disks, but on the 8" ones I just flexed the envelope a bit and fit the hole punch between the disk media & the envelope. Repeat for the other side.

 

[_The Doctor__]

There were specific 5 1/4 disk index punchers for the purpose, I on the other hand had a template as well, Using a protective piece of card stock, I simply flexed the jacket and punched the hole on both side... it's cake.

Edited June 10, 2020 by _The Doctor__

[Mathy]

Hello Stephen

 

3 hours ago, Stephen said:

Didn't it also write data on the backside "backwards" - meaning it couldn't just be flipped over in a single sided drive like 1050 (even if 1050 was capable of reading a double density disk)?

 

It's like looking at the front wheel of a bicycle driving through your street: Both you and the neighbor from the other side of the street see the wheel spinning.  But to you it's spinning in one direction and to that neighbor, it's spinning in the other direction.

 

Sincerely

 

Mathy

[Mathy]

Hello guys

 

I never understood, why you'd want to use SS floppies, when you can store more data on a DS disk and don't have to flip disks.  For commercial use, yes, but for private use...

 

Sincerely

 

Mathy

[+kheller2]

4 hours ago, CharlieChaplin said:

 

Sidenote: Not sure about the 810, can it read the first 720 sectors of a 130k disk or is it unable to do that ? If it can't read a 130k disk at all, then I am wondering why Atari DOS 2.5 used the < and > brackets for 130k disks with files beyond sector 720...?

 

 

Yeah that!  I think we had this discussion on here before, but the 810 is only FM and the 1050 ED is MFM. The 810 couldn't read that data.  So why are the brackets there.  hmmm.  Going through the manual, they are there to notify you that DOS 2.0S would not be able to see them.  I'm assuming that DOS has no idea if the data is FM or MFM and just asks the 1050 for sector information which it happily supplies.   Appendix H of the 2.5 manual is very detailed with examples.

[1050]

The files beyond sector 720 use a second VTOC bit map sector above sector 1023 which DOS 2.0 is completely unaware of. DOS 2.5 shows them with the brackets <   > .  1023 sectors was the limit for sector counting as the three end bytes also needed bits for file number merged within the first two bytes of the last three bytes. This left 0x3FF (1023) as the last usable sector. The second VTOC of DOS 2.5 was I believe at sector 1024 and 1025 thru 1040 were wasted space. So many ways it's not so very compatible with any other DOS. But I used the devil out of it in the years before I had a ramdisk.

[+Larry]

Dos 2.5 w/1040 sectors seems to have been widely used in Europe/UK.  Not so much here in the US.  It just seems to cause another source of incompatibility. (I've seen folks really rail about the incompatibility.)  My solution was MyDos, although it is (IIRC) read-compatible with the Dos 2.5 extended, but not write-compatible. Dunno about Sparta, but I'd bet that SDX can handle all situations. Personally, not a fan -- I see Dos 2.5 extended as a kludge.

[Mathy]

Hello Larry

 

DOS 2.5 ED is a kludge.  It uses two VTOC's that have a huge overlap.  Meaning a lot of sectors are covered in both VTOCs.

 

Sincerely

 

Mathy

[_The Doctor__]

The only good thing about the overlap was vtoc recovery/reconstruction... that an sometimes tricky use where one didn't match the other on purpose.

Edited June 13, 2020 by _The Doctor__

[djglish]

Glad I found this topic.  I have an Enhancer in my XF551 but couldn't remember what it was for. 

 

Just recently started looking at my old Atari stuff again.  I'm having troubles with getting "boot error" going down the screen when I try to use this drive as drive 1 (it was drive 2 originally).  I'm going to have to remember how to work with 8bit systems again.  The other XF551 works great.

[+Nezgar]

On 6/10/2020 at 5:51 PM, kheller2 said:

On 6/10/2020 at 1:22 PM, CharlieChaplin said:

Sidenote: Not sure about the 810, can it read the first 720 sectors of a 130k disk or is it unable to do that ? If it can't read a 130k disk at all, then I am wondering why Atari DOS 2.5 used the < and > brackets for 130k disks with files beyond sector 720...?

Yeah that!  I think we had this discussion on here before, but the 810 is only FM and the 1050 ED is MFM. The 810 couldn't read that data.  So why are the brackets there.  hmmm.  Going through the manual, they are there to notify you that DOS 2.0S would not be able to see them.  I'm assuming that DOS has no idea if the data is FM or MFM and just asks the 1050 for sector information which it happily supplies.   Appendix H of the 2.5 manual is very detailed with examples.

 

Correct - 1050 ED is MFM, so it's physically impossible for an 810 to read. The brackets would have been for when DOS 2.0S was used with a 1050, reading an ED formatted disk.

 

I wrote about it in a bit more detail previously here: https://atariage.com/forums/topic/282461-dos-disks-density-and-sector-counts-education-question/?tab=comments#comment-4102968

 

[Marius]

On 6/10/2020 at 12:55 PM, Larry said:

I've also read that on some European models, you could not even write to the back side. (?) 

There is already a lot written in this thread, but let me specify this part. There are XF551's with different mechanism. One of the 'latest' batches of the XF551 had the so called CHINON mechanism. 

 

It is true that all the XF551's can not format a flippy disk. So where you can flip a disk on a 1050 and format the backside like a normal 1050 format (single side of course), you can not do this on any stock XF551. 

When you format a B: side of a floppy on a 1050 you can also write on this side using an XF551 when you flip the disk. EXCEPT on the Chinon XF551!

 

The Chinon mechanism simply can not handle flippy disks, since it uses the index hole for both formatting, reading AND writing. 

 

The simplest solution for this problem is using floppy disks with two index holes. A few years ago someone offered these disks, so I have a very small stock of 5.25" disks with two index holes. Looks pretty odd, but it worked like a charm. Today I stick with my 1050 with Mini Speedy, so I don't have this problem at all.

 

Summarized:

formatting B: side on a flippy disk: impossible on any XF551

writing on B: side on a flippy disk: XF551 with most mechanisms can do this, except chinon drives.

reading on B: side on a flippy disk: XF551 with most mechanisms an do this, except chinon drives. 

 

IIRC most XF551's have a mitsumi brand mechanism. 

 

Of course, just like @Mathy

already pointed out, all XF551's can write on both sides of the disk, since it is a two-headed mechanism. So that is why I wrote about 'flippy' disks, since a lot of a8 users (and C64, apple ][ users) are used to flip disks. The main reason by the way Mathy, I do not use double sided format is simply because I do not want to limit myself to XF551 drive. I even have been limited myself to 90K format, because I hate ED, and I wanted to be compatible with all my stock 1050 drives. Today I stick with 180K format, since I have many mini-speedy's, so I am secure enough to use 180K format.