Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
> On Sat, 7 Jun 2008 03:48:44 -0700 (PDT), "mscotgrove@aol.com"
> <mscotgrove@aol.com> put finger to keyboard and composed:
>>HD 5.25" drives were dual speed as the 1.2MB disks span at 360 rpm,
>>and not 300 rpm.
> If you mean that HD drives would spin at 360RPM for 1.2MB diskettes
> and at 300RPM for 360KB diskettes, then I don't believe this is true
> for all HD drives, if any. My copy of IBM's original technical
> reference for the PC AT states that the High Capacity Diskette Drive
> had a rotational speed of 360RPM. There is a circuit diagram of the
> main FDD PCB, but not for the motor control board. Nevertheless there
> appears to be only one signal going to the motor PCB and that is Motor
> ON.
This is not a multi-speed motor. 360rpm for everything,
as you state. Since 300rpm is the floppy standard, this
requires a special floppy controller that can deal with
two different data rates.
>>They are also 96tpi rather than 48tpi.
> According to IBM's original technical reference for the PC AT, HD
> 5.25" drives were 96TPI. Confusingly, the manual also lists *exactly*
> the same specs for DD drives as for HD drives (eg 1.2MB formatted
> capacity, 600-650 Oersted media coercivity), even though it states
> that the DD drive is limited to 320/360KB capacity. <shrug> I suspect
> this is an error.
DD is actually 640/720kB when done dual-sided and it is 96TPI.
>>The HD 5.25" disk emulates the DD 8" disk.
> A 360KB formatted capacity is achieved with 2 sides, 40 tracks per
> side, 9 sectors per track. There are 512 data bytes per sector.
Alternatively it is done wit one side and 80 tracks. This
requires a DD disk.
> A 1.2MB formatted capacity is achieved with 2 sides, 80 tracks per
> side, 15 sectors per track.
> A 720KB formatted capacity (3.5" drive) is achieved with 2 sides, 80
> tracks per side, 9 sectors per track.
A double-sided DD disk.
> A 1.44MB formatted capacity is achieved with 2 sides, 80 tracks per
> side, 18 sectors per track.
And HD 3.5" disk, that spins at 300rpm. (Don't think there were single sided
HD disks.)
>>When I last 'played' with floppy disks some years ago I do remember
>>that some modern disk controllers did not handle all old densities.
>>It is possible you have an issue with the controller rather than the
>>physical drive.
>>
>>With the correct controller, all HD drives will read DD disks
>>
>>Michael
> A 720KB 3.5" diskette rotating at 300RPM would produce a data rate of
> 2700 sectors per minute. A 360KB diskette rotating at 360RPM would
> produce a data rate of 3240 sectors per minute. A 1.44MB diskette
> rotating at 300RPM would produce a data rate of 5400 sectors per
> minute. Therefore it seems to me that a controller that can read a
> 720KB 3.5" diskette should easily handle a 360KB 5.25" diskette, if
> the issue is the range of the PLL/VCO in the clock/data separator.
WIth a 5.25" DD drive, no problem at all. With a 5.25" HD
drive, the 20% faster speed may just be within the range
it can still syncronize on. You cannot write though. However
a PC floppy controller can deal with 360rpm by increasing
the speed of everything. You just need BIOS support and need
to configure your drive as 5.25" HD.
Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
> On Mon, 9 Jun 2008 18:37:47 -0700 (PDT), "mscotgrove@aol.com"
> <mscotgrove@aol.com> put finger to keyboard and composed:
>>The data rate for 5.25" disks is 125KHz (SD), 250KHz (DD) or 500KHz
>>(HD)
>>
>>For 8" it was just 250KHz and 500KHz, always at 360 rpm
>>
>>The difference in capacity is the speed of rotaion. A faster rotation
>>with fixed data rate gives a lower capcity
>>
>>(1.44 * 300) / 360 = 1.20
> That's all very well, but if a 360KB DD diskette was written at 250kHz
> in a 300RPM DD drive, then the same diskette in a 360RPM HD drive will
> be read at 300kHz by the controller. That's because the controller
> derives its data clock from the sync bytes just before the sector
> data. The HD drive doesn't slow down to 300RPM to match the original
> recording speed. At least that is the case for the original IBM PC AT
> drives.
The data rate is not derived from the sync byte. It is set by the
controlling software. There is a physical line if the floppy cable
that signals "HD". If it is known to be a 5.25" HD drive the faster
data rate is set by softtware if the HD line is not asserted.
>>I seem to remember there is a density line on the disk drive, but I am
>>currently 7,000 mile from my office an 15 years since I last designed
>>a floppy disk controller
>>
>>Michael
>>www.cnwrecovery.com.
> There is a "reduced write current" output signal from the FD
> controller on pin 2. The HD drive sees this as a Low Density signal
> and uses it to reduce the current to the write amps. In the PC AT case
> this signal does not appear to have any other function. There is
> certainly nothing to vary the speed of the drive. In any case this
> signal is not relevant during reading.
Drive speed is constant. Floppy time base will be adjusted by software
if a DD disk is in a HD drivve (5.25").
On 10 Jun 2008 07:26:03 GMT, Arno Wagner <me@privacy.net> put finger
to keyboard and composed:
>Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
>> On Mon, 9 Jun 2008 18:37:47 -0700 (PDT), "mscotgrove@aol.com"
>> <mscotgrove@aol.com> put finger to keyboard and composed:
>
>>>The data rate for 5.25" disks is 125KHz (SD), 250KHz (DD) or 500KHz
>>>(HD)
>>>
>>>For 8" it was just 250KHz and 500KHz, always at 360 rpm
>>>
>>>The difference in capacity is the speed of rotaion. A faster rotation
>>>with fixed data rate gives a lower capcity
>>>
>>>(1.44 * 300) / 360 = 1.20
>
>> That's all very well, but if a 360KB DD diskette was written at 250kHz
>> in a 300RPM DD drive, then the same diskette in a 360RPM HD drive will
>> be read at 300kHz by the controller. That's because the controller
>> derives its data clock from the sync bytes just before the sector
>> data. The HD drive doesn't slow down to 300RPM to match the original
>> recording speed. At least that is the case for the original IBM PC AT
>> drives.
>
>The data rate is not derived from the sync byte. It is set by the
>controlling software.
The number of sectors per track is set by the software during the
initial formatting. This indirectly determines the data rate. During
formatting, the controller's PLL must be locked to the diskette's
index pulse because that is the only available positional reference.
Afterwards the clock (and therefore the data rate) is derived from the
sync bytes which were written during formatting and which precede the
data area of the sector being written to, or read from. These sync
bytes train the PLL just prior to writing.
>There is a physical line if the floppy cable
>that signals "HD". If it is known to be a 5.25" HD drive the faster
>data rate is set by softtware if the HD line is not asserted.
The floppy drive has no way of telling the controller whether it is a
low density or high density drive. The 5.25" cannot detect whether it
has a lo-den or hi-den diskette, but the 3.5" diskette can. The latter
automatically adjusts its write current without help from the
controller. However, neither drive type can tell the controller what
kind of diskette is present. The interface just doesn't have a signal
for this.
Note that software can detect the presence of a 48TPI drive or a 96TPI
drive. AFAIK it does this by driving the heads toward their end of
travel and then stepping backwards toward track 0. If there are 40 or
so steps before the track 0 sensor is triggered, then a 48TPI drive is
sensed. I believe this accounts for the FDD grunting you hear during
the POST, at least on early PCs.
>>>I seem to remember there is a density line on the disk drive, but I am
>>>currently 7,000 mile from my office an 15 years since I last designed
>>>a floppy disk controller
>>>
>>>Michael
>>>www.cnwrecovery.com.
>
>> There is a "reduced write current" output signal from the FD
>> controller on pin 2. The HD drive sees this as a Low Density signal
>> and uses it to reduce the current to the write amps. In the PC AT case
>> this signal does not appear to have any other function. There is
>> certainly nothing to vary the speed of the drive. In any case this
>> signal is not relevant during reading.
>
>Drive speed is constant. Floppy time base will be adjusted by software
>if a DD disk is in a HD drivve (5.25").
>
>Arno
See above.
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
On 10 Jun 2008 07:21:35 GMT, Arno Wagner <me@privacy.net> put finger
to keyboard and composed:
>Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
>> On Sat, 7 Jun 2008 03:48:44 -0700 (PDT), "mscotgrove@aol.com"
>> <mscotgrove@aol.com> put finger to keyboard and composed:
>
>>>HD 5.25" drives were dual speed as the 1.2MB disks span at 360 rpm,
>>>and not 300 rpm.
>
>> If you mean that HD drives would spin at 360RPM for 1.2MB diskettes
>> and at 300RPM for 360KB diskettes, then I don't believe this is true
>> for all HD drives, if any. My copy of IBM's original technical
>> reference for the PC AT states that the High Capacity Diskette Drive
>> had a rotational speed of 360RPM. There is a circuit diagram of the
>> main FDD PCB, but not for the motor control board. Nevertheless there
>> appears to be only one signal going to the motor PCB and that is Motor
>> ON.
>
>This is not a multi-speed motor. 360rpm for everything,
>as you state. Since 300rpm is the floppy standard, this
>requires a special floppy controller that can deal with
>two different data rates.
AFAICS it just requires a single PLL that can lock to a wider range of
frequencies. I haven't yet seen a controller that couldn't handle a
720KB 3.5" drive. Its data rate is 2700 sectors per minute. A 360KB DD
5.25" drive has the same number of sectors/track (9), and spins at the
same speed (300RPM). Therefore it has the same data rate and should be
electrically indistinguishable from a 720KB 3.5" drive (apart from a
lesser number of tracks). A 360KB diskette in a faster drive should
pose no problem since its data rate would fall in the middle of the
PLL's range. Of course I'm assuming that the controller doesn't have
two different PLLs, one for each drive type.
"Finally in 1983 DOS 2.0 supported 9 sectors per track rather than 8,
providing 180 KB on a (formatted) single-sided disk and 360 KB on a
double-sided."
Do the maths and you'll find that equates to 40 tracks per side.
>> According to IBM's original technical reference for the PC AT, HD
>> 5.25" drives were 96TPI. Confusingly, the manual also lists *exactly*
>> the same specs for DD drives as for HD drives (eg 1.2MB formatted
>> capacity, 600-650 Oersted media coercivity), even though it states
>> that the DD drive is limited to 320/360KB capacity. <shrug> I suspect
>> this is an error.
>
>DD is actually 640/720kB when done dual-sided and it is 96TPI.
See above. BTW I do have Nashua DSDD and DSQD 96TPI diskettes.
>>>The HD 5.25" disk emulates the DD 8" disk.
>
>> A 360KB formatted capacity is achieved with 2 sides, 40 tracks per
>> side, 9 sectors per track. There are 512 data bytes per sector.
>
>Alternatively it is done wit one side and 80 tracks. This
>requires a DD disk.
>
>> A 1.2MB formatted capacity is achieved with 2 sides, 80 tracks per
>> side, 15 sectors per track.
>
>> A 720KB formatted capacity (3.5" drive) is achieved with 2 sides, 80
>> tracks per side, 9 sectors per track.
>
>A double-sided DD disk.
>
>> A 1.44MB formatted capacity is achieved with 2 sides, 80 tracks per
>> side, 18 sectors per track.
>
>And HD 3.5" disk, that spins at 300rpm. (Don't think there were single sided
>HD disks.)
>
>>>When I last 'played' with floppy disks some years ago I do remember
>>>that some modern disk controllers did not handle all old densities.
>>>It is possible you have an issue with the controller rather than the
>>>physical drive.
>>>
>>>With the correct controller, all HD drives will read DD disks
>>>
>>>Michael
>
>> A 720KB 3.5" diskette rotating at 300RPM would produce a data rate of
>> 2700 sectors per minute. A 360KB diskette rotating at 360RPM would
>> produce a data rate of 3240 sectors per minute. A 1.44MB diskette
>> rotating at 300RPM would produce a data rate of 5400 sectors per
>> minute. Therefore it seems to me that a controller that can read a
>> 720KB 3.5" diskette should easily handle a 360KB 5.25" diskette, if
>> the issue is the range of the PLL/VCO in the clock/data separator.
>
>WIth a 5.25" DD drive, no problem at all. With a 5.25" HD
>drive, the 20% faster speed may just be within the range
>it can still syncronize on.
That would only be a problem if the controller used two different
PLLs. Otherwise it should be easier to sync with the faster drive. See
above.
> You cannot write though.
AFAICS, the same PLL is used for reading and writing. If you can do
one, then you can do the other.
>However
>a PC floppy controller can deal with 360rpm by increasing
>the speed of everything. You just need BIOS support and need
>to configure your drive as 5.25" HD.
>
>Arno
If you could spin your 3.5" drive at 360RPM, then your BIOS or OS
wouldn't know the difference.
In fact I just tried configuring my 1.44MB drive as a 1.2MB FD, and my
1.2MB as a 1.44MB FD, and was still able to read 1.44MB and 1.2MB
diskettes in their respective drives. However, I wasn't able to read a
5.25" 360KB diskette when the 5.25" HD drive was configured as a
1.44MB FD.
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
On Tue, 10 Jun 2008 19:40:19 +1000, Franc Zabkar
<fzabkar@iinternode.on.net> wrote:
>On Tue, 10 Jun 2008 18:51:40 +1000, Franc Zabkar
><fzabkar@iinternode.on.net> put finger to keyboard and composed:
>
>>The 5.25" cannot detect whether it
>>has a lo-den or hi-den diskette, but the 3.5" diskette can.
>
>Sorry, that should read ...
>
>"The 5.25 inch drive cannot detect whether it has a lo-den or hi-den
>diskette, but the 3.5" drive can."
>
>- Franc Zabkar
Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
> On 10 Jun 2008 07:26:03 GMT, Arno Wagner <me@privacy.net> put finger
> to keyboard and composed:
>>Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
>>> On Mon, 9 Jun 2008 18:37:47 -0700 (PDT), "mscotgrove@aol.com"
>>> <mscotgrove@aol.com> put finger to keyboard and composed:
>>
>>>>The data rate for 5.25" disks is 125KHz (SD), 250KHz (DD) or 500KHz
>>>>(HD)
>>>>
>>>>For 8" it was just 250KHz and 500KHz, always at 360 rpm
>>>>
>>>>The difference in capacity is the speed of rotaion. A faster rotation
>>>>with fixed data rate gives a lower capcity
>>>>
>>>>(1.44 * 300) / 360 = 1.20
>>
>>> That's all very well, but if a 360KB DD diskette was written at 250kHz
>>> in a 300RPM DD drive, then the same diskette in a 360RPM HD drive will
>>> be read at 300kHz by the controller. That's because the controller
>>> derives its data clock from the sync bytes just before the sector
>>> data. The HD drive doesn't slow down to 300RPM to match the original
>>> recording speed. At least that is the case for the original IBM PC AT
>>> drives.
>>
>>The data rate is not derived from the sync byte. It is set by the
>>controlling software.
> The number of sectors per track is set by the software during the
> initial formatting. This indirectly determines the data rate. During
> formatting, the controller's PLL must be locked to the diskette's
> index pulse because that is the only available positional reference.
Position, yes.
> Afterwards the clock (and therefore the data rate) is derived from the
> sync bytes which were written during formatting and which precede the
> data area of the sector being written to, or read from. These sync
> bytes train the PLL just prior to writing.
There is no PLL actually. Have a look at the design of a floppy
controller. The clock in the controller is fixed during reading and
writing. It does syncronize to a slight degree on the input data
stream (1/16 or 1/64 pulse width per pulse seen, as far as I
remember), but that is not a PLL mechanism, as no locking ever
occures.
>>There is a physical line if the floppy cable
>>that signals "HD". If it is known to be a 5.25" HD drive the faster
>>data rate is set by softtware if the HD line is not asserted.
> The floppy drive has no way of telling the controller whether it is a
> low density or high density drive. The 5.25" cannot detect whether it
> has a lo-den or hi-den diskette, but the 3.5" diskette can. The latter
> automatically adjusts its write current without help from the
> controller. However, neither drive type can tell the controller what
> kind of diskette is present. The interface just doesn't have a signal
> for this.
Hmm. You are right, the HD line goes to the floppy.
> Note that software can detect the presence of a 48TPI drive or a 96TPI
> drive. AFAIK it does this by driving the heads toward their end of
> travel and then stepping backwards toward track 0. If there are 40 or
> so steps before the track 0 sensor is triggered, then a 48TPI drive is
> sensed. I believe this accounts for the FDD grunting you hear during
> the POST, at least on early PCs.
On PCs you set this in the BIOS today. The seek is obsolete.
Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
> On 10 Jun 2008 07:21:35 GMT, Arno Wagner <me@privacy.net> put finger
> to keyboard and composed:
>>Previously Franc Zabkar <fzabkar@iinternode.on.net> wrote:
>>> On Sat, 7 Jun 2008 03:48:44 -0700 (PDT), "mscotgrove@aol.com"
>>> <mscotgrove@aol.com> put finger to keyboard and composed:
>>
>>>>HD 5.25" drives were dual speed as the 1.2MB disks span at 360 rpm,
>>>>and not 300 rpm.
>>
>>> If you mean that HD drives would spin at 360RPM for 1.2MB diskettes
>>> and at 300RPM for 360KB diskettes, then I don't believe this is true
>>> for all HD drives, if any. My copy of IBM's original technical
>>> reference for the PC AT states that the High Capacity Diskette Drive
>>> had a rotational speed of 360RPM. There is a circuit diagram of the
>>> main FDD PCB, but not for the motor control board. Nevertheless there
>>> appears to be only one signal going to the motor PCB and that is Motor
>>> ON.
>>
>>This is not a multi-speed motor. 360rpm for everything,
>>as you state. Since 300rpm is the floppy standard, this
>>requires a special floppy controller that can deal with
>>two different data rates.
> AFAICS it just requires a single PLL that can lock to a wider range of
> frequencies.
There is no PLL in a floppy controller.
> I haven't yet seen a controller that couldn't handle a
> 720KB 3.5" drive. Its data rate is 2700 sectors per minute. A 360KB DD
> 5.25" drive has the same number of sectors/track (9), and spins at the
> same speed (300RPM). Therefore it has the same data rate and should be
> electrically indistinguishable from a 720KB 3.5" drive (apart from a
> lesser number of tracks). A 360KB diskette in a faster drive should
> pose no problem since its data rate would fall in the middle of the
> PLL's range. Of course I'm assuming that the controller doesn't have
> two different PLLs, one for each drive type.
Have a look at a floppy controller manual. You can set the clock
divisor and it has to be set for the expected data rate in order
for this to work. You need it anyways, since writes cannot
synchronize on anything.
> "Finally in 1983 DOS 2.0 supported 9 sectors per track rather than 8,
> providing 180 KB on a (formatted) single-sided disk and 360 KB on a
> double-sided."
> Do the maths and you'll find that equates to 40 tracks per side.
Are you sure there ever were drives for 40 tracks double sided?
>>> According to IBM's original technical reference for the PC AT, HD
>>> 5.25" drives were 96TPI. Confusingly, the manual also lists *exactly*
>>> the same specs for DD drives as for HD drives (eg 1.2MB formatted
>>> capacity, 600-650 Oersted media coercivity), even though it states
>>> that the DD drive is limited to 320/360KB capacity. <shrug> I suspect
>>> this is an error.
>>
>>DD is actually 640/720kB when done dual-sided and it is 96TPI.
> See above. BTW I do have Nashua DSDD and DSQD 96TPI diskettes.
So?? I have thrown away some 5.25" DSDD and DSHD (HD=QD)
sisks too. Where is the problem here?
>>>>The HD 5.25" disk emulates the DD 8" disk.
>>
>>> A 360KB formatted capacity is achieved with 2 sides, 40 tracks per
>>> side, 9 sectors per track. There are 512 data bytes per sector.
>>
>>Alternatively it is done wit one side and 80 tracks. This
>>requires a DD disk.
>>
>>> A 1.2MB formatted capacity is achieved with 2 sides, 80 tracks per
>>> side, 15 sectors per track.
>>
>>> A 720KB formatted capacity (3.5" drive) is achieved with 2 sides, 80
>>> tracks per side, 9 sectors per track.
>>
>>A double-sided DD disk.
>>
>>> A 1.44MB formatted capacity is achieved with 2 sides, 80 tracks per
>>> side, 18 sectors per track.
>>
>>And HD 3.5" disk, that spins at 300rpm. (Don't think there were single sided
>>HD disks.)
>>
>>>>When I last 'played' with floppy disks some years ago I do remember
>>>>that some modern disk controllers did not handle all old densities.
>>>>It is possible you have an issue with the controller rather than the
>>>>physical drive.
>>>>
>>>>With the correct controller, all HD drives will read DD disks
>>>>
>>>>Michael
>>
>>> A 720KB 3.5" diskette rotating at 300RPM would produce a data rate of
>>> 2700 sectors per minute. A 360KB diskette rotating at 360RPM would
>>> produce a data rate of 3240 sectors per minute. A 1.44MB diskette
>>> rotating at 300RPM would produce a data rate of 5400 sectors per
>>> minute. Therefore it seems to me that a controller that can read a
>>> 720KB 3.5" diskette should easily handle a 360KB 5.25" diskette, if
>>> the issue is the range of the PLL/VCO in the clock/data separator.
>>
>>WIth a 5.25" DD drive, no problem at all. With a 5.25" HD
>>drive, the 20% faster speed may just be within the range
>>it can still syncronize on.
> That would only be a problem if the controller used two different
> PLLs. Otherwise it should be easier to sync with the faster drive. See
> above.
No PLL in an FDC. Not even a digital one.
>> You cannot write though.
> AFAICS, the same PLL is used for reading and writing. If you can do
> one, then you can do the other.
No PLL in an FDC.
>>However
>>a PC floppy controller can deal with 360rpm by increasing
>>the speed of everything. You just need BIOS support and need
>>to configure your drive as 5.25" HD.
>>
>>Arno
> If you could spin your 3.5" drive at 360RPM, then your BIOS or OS
> wouldn't know the difference.
It would, sicne my disks would become unreadable.
> In fact I just tried configuring my 1.44MB drive as a 1.2MB FD, and my
> 1.2MB as a 1.44MB FD, and was still able to read 1.44MB and 1.2MB
> diskettes in their respective drives.
That is unsurprising. Both situations deliver the standard,
2ms-clocked MFM signal that the controller expects per default with
HD. You would have to put a 3.5" disk into the 5.25" drive so simulate
the other thing. No adjustment for drive speed id needed with HD of
either size.
> However, I wasn't able to read a
> 5.25" 360KB diskette when the 5.25" HD drive was configured as a
> 1.44MB FD.
And here is the problem that this gives a 3.3ms clocked MFM
instead of a 4ms clocked one that is expected for a DD disk. The
controller cannot handle a deviation this large. And since
the drive was set to 3.5" no, test whether it actually was
a 360rmp drive. You just proved my point.
Previously JW <none@dev.null> wrote:
> On 10 Jun 2008 13:10:48 GMT Arno Wagner <me@privacy.net> wrote in Message
> id: <6b7cqoF39sur0U1@mid.individual.net>:
>>There is no PLL in a floppy controller.
> !
> Of course there is. Pull down a datasheet for a FDC37C665GT or similar.
Interesting. This thing does indeed claim to use a PLL. Maybe it
does, but I have doubts, as the sync field is far too short to
lock a PLL unless it has a really small catch-window (i.e. too
small for 20% deviation).
However, the PLL is not needed. The 1772 did not use one. A
syncronized digital oscillator is quite enough and cheaper
do build, as it does not need any analog components.
Re: How to play an old floppy disk. 
Linear Mode
