22 Apr
2001
22 Apr
'01
11:42 a.m.
I have a few PCjrs running around, and I've often thought of
either adding 3.5" drives to them, or replacing the standard
5.25" drive with 3.5" drives. The controller only supports
double density data rates (250?), so I'm limited to 720KB
3.5" drives. These are getting hard to find.
I connected a new 1.44MB drive to the controller, and
behold, it worked! (With double density media of course.)
The machine booted from the diskette (which was created from
a 360kb image prepared on a Linux machine), and it also ran
diagnostics. So now I'm confused - why did it work?
Does the modern 1.44MB drive sense that the controller is
only sending data at 250KHz rate? If so, how is it doing
the sensing? (The reduced write-current pin (2) isn't
being used - I verified that with a meter.)
Thanks,
Mike
22 Apr
22 Apr
9:06 a.m.
Date: Sun, 22 Apr 2001 11:42:15 -0500
From: Michael Brutman <mbbrutman(a)chartermi.net>
To: classiccmp(a)classiccmp.org
Subject: Using a 1.44MB 3.5inch floppy on an old controller
Reply-to: classiccmp(a)classiccmp.org
I have a few PCjrs running around, and I've often
thought of
either adding 3.5" drives to them, or replacing the standard
5.25" drive with 3.5" drives. The controller only supports
double density data rates (250?), so I'm limited to 720KB
3.5" drives. These are getting hard to find.
Correct, only source of this 720K drives are from scrapped machines.
That 720K drives must be very few in number compared to 360K and
1.22M drives.
a 360kb image prepared on a Linux machine), and it
also ran
diagnostics. So now I'm confused - why did it work?
You have answer. :-) I did this too before on XT and odd balls for
that reason. Also Dos 3.3 supports 720K natively.
Both 720K and 1.44MB are same layout only in 80 tracks only
differences are in type of media and number of sectors per track. 9
for 720K and 18 sectors for 1.44MB. Spun at same 300rpm, therefore
same data rate on 720K due to 9 sectors and also same thing for 360K
except it is 40 tracks. For single sided 180K that's same story, 9
sectors.
Does the modern 1.44MB drive sense that the controller is
only sending data at 250KHz rate? If so, how is it doing
the sensing? (The reduced write-current pin (2) isn't
being used - I verified that with a meter.)
That is input not output, controlled by the controller side also the
drive itself automatically change write current also when it sense on
type of floppy itself via that hole. I think.
Cheers,
Wizard
1:33 p.m.
And to think that I've been worrying about finding thos 720KB
drive. It looks like I don't need them.
I know that the drive senses the media and adjusts the write
current accordingly, to get around a bug in older drive
controllers. But I'm still confused about how the drive
talks to the controller. The PCjr will still try to format
a HD disk - it will just fail.
I'm not a hardware engineer, but it would seem reasonable to
me that the controller and the drive always talk at the 250KHz
rate, because the controller can't do anything else. For
double density media this is fine, and the 1.44MB drive looks
and smells just like a real 720KB drive. However, upon using
a high density disk, commands to read and write data fail
because the drive knows it has high density media, but it is
still talking to the floppy controller at 250KHz (instead of
500KHz).
Is this correct? Or does the drive sense that it has
high density media, adjust it's data transfer rate to 500KHz,
and then fail because the controller doesn't know what's
going on?
While we're on the topic, what do people use for archiving
copy protected disks? I've tried older versions of TeleDisk,
but it really has a hard time with Sargon III which makes me
wonder if it is working reliably on my other titles.
Thanks,
Mike
4:11 p.m.
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7:55 p.m.
On Sun, 22 Apr 2001 22:11:30 +0100 (BST), Tony Duell wrote:
#[1] Actually, the PC/AT controller will _also_ do 300kbps. This is a
#kludge to correctly read 5.25" DD disks (recorded at 250kbps in a
300rpm
#drive) in an HD 5.25" drive (which turns at 360rpm.
This kludge is unnecessary, of course, if you are using a dual speed
drive (such as some of the TEAC HD drives) with a dual speed controller
(the floppy controller on many Adaptec cards, such as the 1540B, can be
set up this way).
Then, since the drive is always running at the "right" speed for the
type of disk, there is no need to have different data rates.
Louis
23 Apr
23 Apr
1:25 p.m.
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22 Apr
22 Apr
12:52 p.m.
It's simpler than that. The drive recognizes the media as HD or DD by
the hole (or lack of hole). So the drive uses DD, which is acceptable
to the controller, when you use DD media. If you put in HD media, and
taped over the hole, it would work as well.
Louis
On Sun, 22 Apr 2001 11:42:15 -0500, Michael Brutman wrote:
#I have a few PCjrs running around, and I've often thought of
#either adding 3.5" drives to them, or replacing the standard
#5.25" drive with 3.5" drives. The controller only supports
#double density data rates (250?), so I'm limited to 720KB
#3.5" drives. These are getting hard to find.
#
#I connected a new 1.44MB drive to the controller, and
#behold, it worked! (With double density media of course.)
#The machine booted from the diskette (which was created from
#a 360kb image prepared on a Linux machine), and it also ran
#diagnostics. So now I'm confused - why did it work?
#
#Does the modern 1.44MB drive sense that the controller is
#only sending data at 250KHz rate? If so, how is it doing
#the sensing? (The reduced write-current pin (2) isn't
#being used - I verified that with a meter.)
#
#Thanks,
#Mike
#
1:08 p.m.
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