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Article #54 (74 is last):
From: aa700@cleveland.Freenet.Edu (Michael Current)
Subject: XF551 / hardware
Posted-By: xx004 (aa700 - Michael Current)
Reply-To: aa700@cleveland.Freenet.Edu (Michael Current)
Date: Sat May 16 00:39:49 1992

Reprinted from the Pandora BBS (614)-471-9209

A Review of the XF-551
by Robert Puff

 Atari's new XF-551 certainly has been quite a surprise to many. I have seen 
many comments concerning it, and thought I would offer some of mine as well.
 The drive is just about the same size as the 1050, but not quite as high. It 
uses a generic-type double-sided direct drive mechanism which is nice and quiet, 
compared to some 1050's I've heard. The drive uses the standard 9VAC power 
supplies used for the other 1050 and 810 drives. The back of the drive does get 
nice and hot, just like the 1050s, but that did not affect the drive's operation 
when I left it running for a month solid.
 The drive runs a little faster (300 RPM compared to the standard 288), but 
Atari adjusted for it by clocking the controller a little faster. So there is 
still the same amount of data in the same format on the disk.
 Now we get into compatability. Atari has done a fair job at making the drive 
compatible with the 810 and 1050. There is only one flaw I found. The missing 
sector bit in the status bytes does not reflect a missing sector correctly. This 
should have been simple enough to do, but they did not. Because of this, there 
ARE protected disks that will not load on a XF-551. I do not have the titles 
with me at the moment, but any program that looks for a missing sector status 
will probably not work.
 The next subject is double density. Finally, Atari has come out with a true 
double density drive, which will read other double density disks. However, there 
are some problems here also. To determine the density of a disk, normally you 
read sector 1, and then issue a status request. One of the status bytes will 
then tell you the density. This works fine for the XF-551 when it is in single 
or enhanced density, but not always for double. Instead, double density comes 
back with a status of enhanced. Once you use the set density commands, the drive 
may be set to double, and the status will be correct. Just don't go back into 
single, or you'll have to manually set the density again. To summarize: If you 
use single and double density disks, the drive will have a very hard time going 
into double. Since SpartaDOS has no way of forcing densities, this can be a real 
problem. The only way I've ever seen it do it automatically is when booting a 
double density disk. (Note: I did figure out a way to make the drive 
reconfigure: It is used in Diskcomm 3.2)
 The drive is capable of double-sided operation, giving you a possible 360K 
storage when using double density. (Of course, you must use MYDOS or SpartaDOS 
because the DOS 2.5 it comes with supports none of this.) I found it strange 
that it will not use double-sided operation in single or enhanced density.
 Also another thing to think about is it uses the index hole of your disks for 
timing. This means you cannot use those cheap hard-sectored disks anymore, and 
cannot write to the back side of the disk like you did with your 1050, 810, 
etc... Now this really dosen't matter if you use its double-sided capabilities; 
but if you want to make up a disk for your club or friend who has a 1050, and 
wish to use the back side, you are out of luck.
 The High-Speed disk I/O the drive boasts is very similar to Happy's 810 warp 
speed. Although not as fast as ICD's UltraSpeed, it is fast. The set-up is 
similar to UltraSpeed: You must format with a special sector skew for optimum 
speed, which will be slow when high-speed software is not used. Strangely 
enough, the drive only has a special sector skew for double density, even though 
the exact same command is used for single density. I have been able to read 
single density disks formatted with UltraSpeed sector skew quite nicely on the 
XF-551. As of now, the only programs I am aware of that make use of the high-
speed capabilities is my Disk Communicator program version 3.2, and THE ULTRA 
 Unfortunately, Atari did not make the drive for expansion. It uses a MCU chip 
that takes the place of many chips the 1050 used. Because of this, and because 
it's not 6502 based, I don't think you will see any products such as the Happy 
or Super Archiver available for a while.
 Well, I guess that's it. I have confirmed the bugs I found with later models, 
so it appears they haven't been fixed yet. Once Atari fixes these, it should be 
a very good drive at a nice price.

 Michael Current, Cleveland Free-Net 8-bit Atari SIGOp   -->>  go atari8  <<--
   The Cleveland Free-Net Atari SIG is the Central Atari Information Network
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