8" disk drive project possibly 3.5" substitution - CP/M

I posted this message to cctalk, but it hasn't seemed to spark a
conversation.

I know my BEST method is to make a SVD type device to emulate the
FD400 used in the Altair. I'm interested in the short term in
modifying a disk cabinet to support a 3.5" disk directly. My main
concern is the lack of some input signals and the lack of actual
physical sectors. COmments on generating the hard sectors from a
16MHz counter dividing the index pulse are wanted...

Here is the cctalk information:

I'm going to add some to my own topic. The questions below still
stand, but I've got more info! : )


I want to use a QUME 842 or SA800 in an altair disk subsystem.

Both seem to have the same interface.

The FD400-5x0-5x1 manual seems to show the drives being quite similar.

The first thing I see is that there are extra signals.

"Trim Erase", "Write Enable", and "Write Data" where the Shugart
interface only has "Write Data" and "Write Gate". I assume that gate
and enable are the same thing. The FD Pertec drives also have "IN",
"OUT", and "STEP" instead of "STEP" and "DIRECTION", but that is not a
big deal. That can be generated in software.

What I don't see is any input to perform the function of head
current. How does the shugart interface handle this?

Can I ignore the trim erase feature? How do I generate a write busy
signal? I'm willing to make some circuits to fake these signals if
required.

More info:

The pinout of an Altair disk drive...of the wires connected. Omitted
pins are either not connected, power, or ground. All lettered
connections are ground.

6 - Output - Door Open (IDOP
7 - Head Current Switch (IHCS)
8 - External Trim Erase (Option) (IEEN)
9 - Input - Write Enable (IWEN)
10 - Input - Write Data Input (IWDA)
11 - Input - Step In (ISTI)
15 - Input - Step Out (ISTO)
16 - Input - Head Load (IHLD)
17 - Output - Index (IINXP)
18 - Input - Drive Motor On (IDEN)
19 - Track 0 (ITRK0)
20 - Output - Read Data Output (IRDA)

One thing that interests me slightly more is the possibility of a
regular 3.5" disk connected to the Altair. I don't care about the
encoding or format being compatible with a standard controller.

It is very similar, but is also a soft sector disk/drive. How close
is close? Can I just use a microcontroller with a timer to time from
one index to the next and divide it up into 32 sectors? Will this be
close enough for the Altair? Anyone know what kinds of errors I would
get? A microcontroller running at 16MHz would be able to count
between pulses with 16MHz/1 accuracy. With the SA800 I would have a
sector hole sensor giving me the correct timing.

There still is the issue of the write trim erase feature, whatever
that is...

Any comments or ideas on the idea? Is it worth trying? I've got a
very weird tarbell card that formats and uses 3.5" disks as a 70k mini
floppy. I guess anything is possible. : )

2 - Density Select (/REDWC)
8 - Index (/INDEX)
10 - Motor Enable Drive 0 (/MOTEA)
12 - Drive Select 1 (/DRVSA)
14 - Drive Select 0 (/DRVSB)
16 - Motor Enable Drive 1 (/MOTEB)
18 - Direction Select (/DIR)
20 - Head Step (/STEP)
22 - Write Data (/WDATE)
24 - Floppy Write Enable (/WGATE)
26 - Track 00 (/TRK0)
28 - Write Protect (/WPT)
30 - Read Data (/RDATA)
32 - Head Select (/SIDE1)
34 - Disk Change/Ready (/DISKCHG)

I'm not going to sleep a wink tonight. I hate having ideas at
10PM... : (

Grant

On Tue, 06 Nov 2007 19:41:04 -0000, Grant Stockly
wrote:

>I posted this message to cctalk, but it hasn't seemed to spark a
>conversation.

I replied to you but it's hung in the server I guess. Several others
did too.

>
>I know my BEST method is to make a SVD type device to emulate the
>FD400 used in the Altair. I'm interested in the short term in
>modifying a disk cabinet to support a 3.5" disk directly. My main
>concern is the lack of some input signals and the lack of actual
>physical sectors. COmments on generating the hard sectors from a
>16MHz counter dividing the index pulse are wanted...
>
>Here is the cctalk information:
>
>I'm going to add some to my own topic. The questions below still
>stand, but I've got more info! : )
>
>
>I want to use a QUME 842 or SA800 in an altair disk subsystem.
>
>Both seem to have the same interface.
>
>The FD400-5x0-5x1 manual seems to show the drives being quite similar.
>
>The first thing I see is that there are extra signals.
>
>"Trim Erase", "Write Enable", and "Write Data" where the Shugart
>interface only has "Write Data" and "Write Gate". I assume that gate
>and enable are the same thing. The FD Pertec drives also have "IN",
>"OUT", and "STEP" instead of "STEP" and "DIRECTION", but that is not a
>big deal. That can be generated in software.
>
>What I don't see is any input to perform the function of head
>current. How does the shugart interface handle this?

head current was also called TG43, not all drives had it. Some that
have it work just as well with it stuck at one level.

>Can I ignore the trim erase feature? How do I generate a write busy
>signal? I'm willing to make some circuits to fake these signals if
>required.

No. It's really called tunnel erase and still on most drives but
without a seperate control. For some reason that drive they have it
as a seperate control. It's usually activated with Write enable.

Write busy is sorta obvious. It's an echo of the write enable
and maybe used for a Door lock enable.

Back then Floppies was VERY new and still in flux standards wise.


Allison
>
>More info:
>
>The pinout of an Altair disk drive...of the wires connected. Omitted
>pins are either not connected, power, or ground. All lettered
>connections are ground.
>
>6 - Output - Door Open (IDOP
>7 - Head Current Switch (IHCS)
>8 - External Trim Erase (Option) (IEEN)
>9 - Input - Write Enable (IWEN)
>10 - Input - Write Data Input (IWDA)
>11 - Input - Step In (ISTI)
>15 - Input - Step Out (ISTO)
>16 - Input - Head Load (IHLD)
>17 - Output - Index (IINXP)
>18 - Input - Drive Motor On (IDEN)
>19 - Track 0 (ITRK0)
>20 - Output - Read Data Output (IRDA)
>
>One thing that interests me slightly more is the possibility of a
>regular 3.5" disk connected to the Altair. I don't care about the
>encoding or format being compatible with a standard controller.
>
>It is very similar, but is also a soft sector disk/drive. How close
>is close? Can I just use a microcontroller with a timer to time from
>one index to the next and divide it up into 32 sectors? Will this be
>close enough for the Altair? Anyone know what kinds of errors I would
>get? A microcontroller running at 16MHz would be able to count
>between pulses with 16MHz/1 accuracy. With the SA800 I would have a
>sector hole sensor giving me the correct timing.
>
>There still is the issue of the write trim erase feature, whatever
>that is...
>
>Any comments or ideas on the idea? Is it worth trying? I've got a
>very weird tarbell card that formats and uses 3.5" disks as a 70k mini
>floppy. I guess anything is possible. : )
>
>2 - Density Select (/REDWC)
>8 - Index (/INDEX)
>10 - Motor Enable Drive 0 (/MOTEA)
>12 - Drive Select 1 (/DRVSA)
>14 - Drive Select 0 (/DRVSB)
>16 - Motor Enable Drive 1 (/MOTEB)
>18 - Direction Select (/DIR)
>20 - Head Step (/STEP)
>22 - Write Data (/WDATE)
>24 - Floppy Write Enable (/WGATE)
>26 - Track 00 (/TRK0)
>28 - Write Protect (/WPT)
>30 - Read Data (/RDATA)
>32 - Head Select (/SIDE1)
>34 - Disk Change/Ready (/DISKCHG)
>
>I'm not going to sleep a wink tonight. I hate having ideas at
>10PM... : (
>
>Grant

Grant Stockly wrote:

> I posted this message to cctalk, but it hasn't seemed to spark a
> conversation.

> I know my BEST method is to make a SVD type device to emulate the
> FD400 used in the Altair. I'm interested in the short term in
> modifying a disk cabinet to support a 3.5" disk directly. My main
> concern is the lack of some input signals and the lack of actual
> physical sectors. COmments on generating the hard sectors from a
> 16MHz counter dividing the index pulse are wanted...

(snip)

> One thing that interests me slightly more is the possibility of a
> regular 3.5" disk connected to the Altair. I don't care about the
> encoding or format being compatible with a standard controller.

> It is very similar, but is also a soft sector disk/drive. How close
> is close? Can I just use a microcontroller with a timer to time from
> one index to the next and divide it up into 32 sectors? Will this be
> close enough for the Altair? Anyone know what kinds of errors I would
> get? A microcontroller running at 16MHz would be able to count
> between pulses with 16MHz/1 accuracy. With the SA800 I would have a
> sector hole sensor giving me the correct timing.

I posted before about using a PLL to fake hard sector pulses.
The PLL could follow speed variations in the long term, though
it might require keeping the motor on. That would be usual for
8 inch drives, anyway.

> There still is the issue of the write trim erase feature, whatever
> that is...

After the data is written another head erases the edge to keep the
track from getting too wide. This helps if the positioning isn't
exactly the same as the previous track, by erasing what would have
been left over. It might require a delay in turning off, as the head
is slightly past the write head. I believe that newer drives do this
automatically.

-- glen

> I posted before about using a PLL to fake hard sector pulses.
> The PLL could follow speed variations in the long term, though
> it might require keeping the motor on. That would be usual for
> 8 inch drives, anyway.

Can you find that post? I found this, which was inspirational...

http://groups.google.com/group/comp....304b80881ef939

It sounds like my biggest problem is going to be finding a 3.5" drive
that produces index pulses during seek operations and has a properly
operating ready line.

I was looking at a 3.5" drive and I got the dangerous idea of hooking
the microcontroller to the stepper motor or stepper motor controller.
I'll have to hook a logic analyzer to the chips and motor and see what
is comming in and out of it. I can't find any data sheets for the
parts.

That might be over kill. Just timing between pulses might be enough.
Hook the head load terminal to the microcontroller so that the uC
starts the motor in the drive, waits for a few index pulses, and then
the uC could tell the Altair through the ready line that everything
was "ready". The Altair expects the drive to spin all the time...

Grant

On Tue, 06 Nov 2007 22:25:30 -0000, Grant Stockly
wrote:

>> I posted before about using a PLL to fake hard sector pulses.
>> The PLL could follow speed variations in the long term, though
>> it might require keeping the motor on. That would be usual for
>> 8 inch drives, anyway.
>
>Can you find that post? I found this, which was inspirational...
>
>http://groups.google.com/group/comp....304b80881ef939
>
>It sounds like my biggest problem is going to be finding a 3.5" drive
>that produces index pulses during seek operations and has a properly
>operating ready line.

Why would you require that? Though I did check mine and they do
though.

>I was looking at a 3.5" drive and I got the dangerous idea of hooking
>the microcontroller to the stepper motor or stepper motor controller.
>I'll have to hook a logic analyzer to the chips and motor and see what
>is comming in and out of it. I can't find any data sheets for the
>parts.
>
>That might be over kill. Just timing between pulses might be enough.
>Hook the head load terminal to the microcontroller so that the uC
>starts the motor in the drive, waits for a few index pulses, and then
>the uC could tell the Altair through the ready line that everything
>was "ready". The Altair expects the drive to spin all the time...

They all do if drive is selected. When I've encountered the need
for a Ready a retriggerable oneshot fired off the index line seems
to be enough to keep things happy.

A lot of the Altair contoller signals can be faked or outright ignored
or worse patched out of the code.

Allison

> They all do if drive is selected. When I've encountered the need
> for a Ready a retriggerable oneshot fired off the index line seems
> to be enough to keep things happy.

But the Altair drives spin the disk even if they are not selected.
Does that sound right? They spin the disk even if they are not
connected to a computer. Door shut, disk spin...

> >That might be over kill. Just timing between pulses might be enough.
> >Hook the head load terminal to the microcontroller so that the uC
> >starts the motor in the drive, waits for a few index pulses, and then
> >the uC could tell the Altair through the ready line that everything
> >was "ready". The Altair expects the drive to spin all the time...
>
> They all do if drive is selected. When I've encountered the need
> for a Ready a retriggerable oneshot fired off the index line seems
> to be enough to keep things happy.

But the Altair drives spin even when they are not selected.

How long will a disk last spinning at 300RPM?

Grant

>One thing that interests me slightly more is the possibility of a
>regular 3.5" disk connected to the Altair. I don't care about the
>encoding or format being compatible with a standard controller.

>It is very similar, but is also a soft sector disk/drive. How close
>is close? Can I just use a microcontroller with a timer to time from
>one index to the next and divide it up into 32 sectors? Will this be
>close enough for the Altair? Anyone know what kinds of errors I would
>get? A microcontroller running at 16MHz would be able to count
>between pulses with 16MHz/1 accuracy. With the SA800 I would have a
>sector hole sensor giving me the correct timing.

This should work - you will need a bit of smarts, not producing indexes
and READY until the drive is up to speed, adjusting timing on the fly to
account for drive speed variation etc. You want it to be as accurate as
possible.

The biggest problem I see is the speed difference - 8" disks
spin at 360 rpm, while a 3.5" drive spins at 300 rpm.

This means that the 8" disk will see a new sector pulse every 5,2 ms,
while the 3.5" disk would see a new sector pulse every 6.25 ms.
Expressed as frequency, it's 192hz .vs. 160hz.

Fortunately it's longer due to the slower drive, so the sector should
fit - both drives use a 500khz data rate - but I don't know if your
controller and software will accept this, I guess you will have to
try and tweak as needed.

A 5.25" HD drive spins at 360rpm, and is closer to an 8" drive than
a 3.5" drive - if you have trouble with the 3.5", you might have better
luck with a 5.25" HD.


>But the Altair drives spin even when they are not selected.
>How long will a disk last spinning at 300RPM?

The trick here is that 8" drives have a head-load solinoid
which removes the heads from the media when it is not
being accessed. The jacket material is low-friction and the
disk will experience very little wear spinning without the
heads loaded.

The 3.5" drive does not have a head-load solinoid and will
cause significant wear on the disk if left in constant operation.
For long term use you should start/stop the drive, however
you will need to allow the drive to come up to speed before
accessing it - which may require mods to your software.


--
dave06a@ Low-cost firmware development tools: www.dunfield.com
dunfield. Classic computer collection: www.classiccmp.org/dunfield
com Some stuff I have for sale: www.dunfield.com/sale

On Wed, 07 Nov 2007 00:15:16 -0800, Grant Stockly
wrote:

>> They all do if drive is selected. When I've encountered the need
>> for a Ready a retriggerable oneshot fired off the index line seems
>> to be enough to keep things happy.
>
>But the Altair drives spin the disk even if they are not selected.
>Does that sound right? They spin the disk even if they are not
>connected to a computer. Door shut, disk spin...

That was common for 8" drives, most ran using an AC motor with
no on/off control. SO even with NO media it spun.

MY SA800/850s do that, MY RX02 (DEC 8" floppy) do that. The only ones
I have that dont are my SA860s (half height with DC motor) and there
is a jumper option to run the motor all the time.

In all cases you only get sector pulses with media in drive and the
door closed and that drive selected.

Allison

On 7 Nov 2007 01:30:28 -0800, Grant Stockly wrote:

>> >That might be over kill. Just timing between pulses might be enough.
>> >Hook the head load terminal to the microcontroller so that the uC
>> >starts the motor in the drive, waits for a few index pulses, and then
>> >the uC could tell the Altair through the ready line that everything
>> >was "ready". The Altair expects the drive to spin all the time...
>>
>> They all do if drive is selected. When I've encountered the need
>> for a Ready a retriggerable oneshot fired off the index line seems
>> to be enough to keep things happy.
>
>But the Altair drives spin even when they are not selected.
>
>How long will a disk last spinning at 300RPM?
>
If the media is good and the heads clean... Dont know, years?
Certainly many hundreds of hours. However the bearings and
motor also have finite life. I've seen both fail.

Allison


>Grant

On Wed, 07 Nov 2007 12:39:01 GMT,
Dave.Dunfield@use.techsupport.link.on.my.website (Dave Dunfield)
wrote:

>>One thing that interests me slightly more is the possibility of a
>>regular 3.5" disk connected to the Altair. I don't care about the
>>encoding or format being compatible with a standard controller.
>
>>It is very similar, but is also a soft sector disk/drive. How close
>>is close? Can I just use a microcontroller with a timer to time from
>>one index to the next and divide it up into 32 sectors? Will this be
>>close enough for the Altair? Anyone know what kinds of errors I would
>>get? A microcontroller running at 16MHz would be able to count
>>between pulses with 16MHz/1 accuracy. With the SA800 I would have a
>>sector hole sensor giving me the correct timing.
>
>This should work - you will need a bit of smarts, not producing indexes
>and READY until the drive is up to speed, adjusting timing on the fly to
>account for drive speed variation etc. You want it to be as accurate as
>possible.
>
>The biggest problem I see is the speed difference - 8" disks
>spin at 360 rpm, while a 3.5" drive spins at 300 rpm.
>
>This means that the 8" disk will see a new sector pulse every 5,2 ms,
>while the 3.5" disk would see a new sector pulse every 6.25 ms.
>Expressed as frequency, it's 192hz .vs. 160hz.
>
>Fortunately it's longer due to the slower drive, so the sector should
>fit - both drives use a 500khz data rate - but I don't know if your
>controller and software will accept this, I guess you will have to
>try and tweak as needed.

The Altair disk was 250khz data rate (signle sided single density)
ignoring the hard sector.


>A 5.25" HD drive spins at 360rpm, and is closer to an 8" drive than
>a 3.5" drive - if you have trouble with the 3.5", you might have better
>luck with a 5.25" HD.

The spin rate is not a real issue as the sector pulses were used like
NS* to locate the sectors on the media. Slower is if anything easier!

Allison
>
>
>>But the Altair drives spin even when they are not selected.
>>How long will a disk last spinning at 300RPM?
>
>The trick here is that 8" drives have a head-load solinoid
>which removes the heads from the media when it is not
>being accessed. The jacket material is low-friction and the
>disk will experience very little wear spinning without the
>heads loaded.
>
>The 3.5" drive does not have a head-load solinoid and will
>cause significant wear on the disk if left in constant operation.
>For long term use you should start/stop the drive, however
>you will need to allow the drive to come up to speed before
>accessing it - which may require mods to your software.

On Nov 6, 5:25 pm, Grant Stockly wrote:
> > I posted before about using a PLL to fake hard sector pulses.
> > The PLL could follow speed variations in the long term, though
> > it might require keeping the motor on. That would be usual for
> > 8 inch drives, anyway.
>
> Can you find that post? I found this, which was inspirational...
>
> http://groups.google.com/group/comp....d/thread/9f662...
>
> It sounds like my biggest problem is going to be finding a 3.5" drive
> that produces index pulses during seek operations and has a properly
> operating ready line.
>
> I was looking at a 3.5" drive and I got the dangerous idea of hooking
> the microcontroller to the stepper motor or stepper motor controller.
> I'll have to hook a logic analyzer to the chips and motor and see what
> is comming in and out of it. I can't find any data sheets for the
> parts.
>
> That might be over kill. Just timing between pulses might be enough.
> Hook the head load terminal to the microcontroller so that the uC
> starts the motor in the drive, waits for a few index pulses, and then
> the uC could tell the Altair through the ready line that everything
> was "ready". The Altair expects the drive to spin all the time...
>
> Grant

Why such extreme complexity? Just use a CompuPro Disk1 and Mitsumi
D359T3 jumpered for 360rpm like I do.

~ J

no.spam@no.uce.bellatlantic.net wrote:

> On 7 Nov 2007 01:30:28 -0800, Grant Stockly wrote:
(snip)

>>How long will a disk last spinning at 300RPM?

> If the media is good and the heads clean... Dont know, years?
> Certainly many hundreds of hours. However the bearings and
> motor also have finite life. I've seen both fail.

I remember and RT-11 system from years ago that was kept running
for a year or two. At one point I looked at the disk, and it was
getting very thin near the hub. It may have been more than two
years.

-- glen

On Wed, 07 Nov 2007 09:46:47 -0800, glen herrmannsfeldt
wrote:

>no.spam@no.uce.bellatlantic.net wrote:
>
>> On 7 Nov 2007 01:30:28 -0800, Grant Stockly wrote:
>(snip)
>
>>>How long will a disk last spinning at 300RPM?
>
>> If the media is good and the heads clean... Dont know, years?
>> Certainly many hundreds of hours. However the bearings and
>> motor also have finite life. I've seen both fail.
>
>I remember and RT-11 system from years ago that was kept running
>for a year or two. At one point I looked at the disk, and it was
>getting very thin near the hub. It may have been more than two
>years.

The head load wasn't active for all that time I hope.

Single sided AC motor drives will spin the media all the time
but the head load solinoid is not active so the amount of
pressure on the media and head is small almost barely
touching. So wear tends to be very low.

The twosided drives have differnt issues as they fall in two forms
head load with door close and those that have a head load solinoid
Wear patterns for those are very different and vary from drive type to
drive type.

Allison

>-- glen

On Nov 7, 12:42 pm, Dave.Dunfi...@use.techsupport.link.on.my.website
(Dave Dunfield) wrote:
> >>Fortunately it's longer due to the slower drive, so the sector should
> >>fit - both drives use a 500khz data rate - but I don't know if your
> >>controller and software will accept this, I guess you will have to
> >>try and tweak as needed.
> >The Altair disk was 250khz data rate (signle sided single density)
> >ignoring the hard sector.
>
> Yes - I was thinking of drives, and DD data rates, not the Altair
> specifically and single-density, however the comment
> stands - both 8" and 3.5" HD disks use the same data rate - it's
> just the rotational speed thats different.

Being a multiple, 250 vs 500, what do you guys think will happen?
Will the drive work without modification to motor speed? : )

> >>A 5.25" HD drive spins at 360rpm, and is closer to an 8" drive than
> >>a 3.5" drive - if you have trouble with the 3.5", you might have better
> >>luck with a 5.25" HD.
> >The spin rate is not a real issue as the sector pulses were used like
> >NS* to locate the sectors on the media. Slower is if anything easier!
>
> Unless there's a one-shot tracking the index pulses to determine
> when the drive is up to speed - I'm not familier with this particular
> controller so it may as you say not be an issue, however it's a
> fairly major difference in the drives which has not been mentioned
> before.

I don't think the Altair controller is quite that smart. Since the
disk starts spinning as soon as the door shuts I imagine it assumes
that it is up to speed. I think the documentation talks about the
Ready line in relation to seeks. The FD400 also used a stepper motor,
so speed shouldn't ever be an issue as long as its ramped up.

>>Fortunately it's longer due to the slower drive, so the sector should
>>fit - both drives use a 500khz data rate - but I don't know if your
>>controller and software will accept this, I guess you will have to
>>try and tweak as needed.

>The Altair disk was 250khz data rate (signle sided single density)
>ignoring the hard sector.

Yes - I was thinking of drives, and DD data rates, not the Altair
specifically and single-density, however the comment
stands - both 8" and 3.5" HD disks use the same data rate - it's
just the rotational speed thats different.


>>A 5.25" HD drive spins at 360rpm, and is closer to an 8" drive than
>>a 3.5" drive - if you have trouble with the 3.5", you might have better
>>luck with a 5.25" HD.

>The spin rate is not a real issue as the sector pulses were used like
>NS* to locate the sectors on the media. Slower is if anything easier!

Unless there's a one-shot tracking the index pulses to determine
when the drive is up to speed - I'm not familier with this particular
controller so it may as you say not be an issue, however it's a
fairly major difference in the drives which has not been mentioned
before.


--
dave06a@ Low-cost firmware development tools: www.dunfield.com
dunfield. Classic computer collection: www.classiccmp.org/dunfield
com Some stuff I have for sale: www.dunfield.com/sale

Grant Stockly wrote:

> I don't think the Altair controller is quite that smart. Since the
> disk starts spinning as soon as the door shuts I imagine it assumes
> that it is up to speed. I think the documentation talks about the
> Ready line in relation to seeks. The FD400 also used a stepper motor,
> so speed shouldn't ever be an issue as long as its ramped up.

Grant, out of curiosity: which MITS/Altair floppy controller are you
using? There were a number of models. Also, it may matter what
software you are using. I don't recall all the details, but some of
those controllers had an on board 8080 and its own code; some may have
only used the S-100 CPU to run code. So, that controller may be
smarter than you think.

You posted earlier that you did not have all the docs. You probably
know to look on my Web pages for MITS and Pertec docs and discussion
of controllers and drives, at this Web link:

http://www.retrotechnology.com/herbs.../d_altair.html

and for other floppy drive docs at this link:

http://www.retrotechnology.com/herbs.../s_drives.html

The Shugart SA800 (early 8" floppy drive) docs are very informative in
general. There are some design docs, and the 800/801 had a circuit to
deal with hard sectoring. Early drive manufacturers wrote about some
of these issues, and put it in their docs. And, you'll find timing and
other information about 3.5" drives in docs for those drives. I have a
Web page where I've accumulated some drive technical information:

http://www.retrotechnology.com/herbs_stuff/drive.html

You asked "for a conversation". Myself, I like to let the manuals do
the "talking".

Herb Johnson

Herbert R. Johnson, New Jersey USA
http://www.retrotechnology.com/herbs_stuff/ web site
http://www.retrotechnology.net/herbs_stuff/ domain mirror
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"Herb's Stuff": old Mac, SGI, 8-inch floppy drives
S-100 IMSAI Altair computers, docs, by "Dr. S-100"

On Wed, 07 Nov 2007 21:23:56 -0000, Grant Stockly
wrote:

>On Nov 7, 12:42 pm, Dave.Dunfi...@use.techsupport.link.on.my.website
>(Dave Dunfield) wrote:
>> >>Fortunately it's longer due to the slower drive, so the sector should
>> >>fit - both drives use a 500khz data rate - but I don't know if your
>> >>controller and software will accept this, I guess you will have to
>> >>try and tweak as needed.
>> >The Altair disk was 250khz data rate (signle sided single density)
>> >ignoring the hard sector.
>>
>> Yes - I was thinking of drives, and DD data rates, not the Altair
>> specifically and single-density, however the comment
>> stands - both 8" and 3.5" HD disks use the same data rate - it's
>> just the rotational speed thats different.
>
>Being a multiple, 250 vs 500, what do you guys think will happen?
>Will the drive work without modification to motor speed? : )
>
>> >>A 5.25" HD drive spins at 360rpm, and is closer to an 8" drive than
>> >>a 3.5" drive - if you have trouble with the 3.5", you might have better
>> >>luck with a 5.25" HD.
>> >The spin rate is not a real issue as the sector pulses were used like
>> >NS* to locate the sectors on the media. Slower is if anything easier!
>>
>> Unless there's a one-shot tracking the index pulses to determine
>> when the drive is up to speed - I'm not familier with this particular
>> controller so it may as you say not be an issue, however it's a
>> fairly major difference in the drives which has not been mentioned
>> before.

Speed is not an issue. the controler doesn't care. it's the
presence or absence that is important and when you read,
write and step things are timed off that. Look at the logic and
read the driver software. It's comples becuase they thought that was
the way to do it knowing no better thats what they did... the hard
way.

>I don't think the Altair controller is quite that smart. Since the
>disk starts spinning as soon as the door shuts I imagine it assumes
>that it is up to speed. I think the documentation talks about the
>Ready line in relation to seeks. The FD400 also used a stepper motor,
>so speed shouldn't ever be an issue as long as its ramped up.


The original two board Altair controller was dumb as a stump. It was
random logic and oneshots no cpu or ram buffers. The NS* SD
controller was very similar in many ways just much simpler and no
analog oneshots.

Allison

>> >>Fortunately it's longer due to the slower drive, so the sector should
>> >>fit - both drives use a 500khz data rate - but I don't know if your
>> >>controller and software will accept this, I guess you will have to
>> >>try and tweak as needed.
>> >The Altair disk was 250khz data rate (signle sided single density)
>> >ignoring the hard sector.
>>
>> Yes - I was thinking of drives, and DD data rates, not the Altair
>> specifically and single-density, however the comment
>> stands - both 8" and 3.5" HD disks use the same data rate - it's
>> just the rotational speed thats different.

>Being a multiple, 250 vs 500, what do you guys think will happen?
>Will the drive work without modification to motor speed? : )

The data rate is not a problem. As Allison pointed out, for an Altair
drive running single-density the data rate is 250 kbps. I was thinking
Double-Density which has a data rate of 500kbps - the 3.5" drive
should be able to do either one (the actual clock rate is not different,
just the encoding method FM .vs. MFM). The tolerances for MFM are
higher, if a drive can do MFM it should be able to do FM.


>> >>A 5.25" HD drive spins at 360rpm, and is closer to an 8" drive than
>> >>a 3.5" drive - if you have trouble with the 3.5", you might have better
>> >>luck with a 5.25" HD.
>> >The spin rate is not a real issue as the sector pulses were used like
>> >NS* to locate the sectors on the media. Slower is if anything easier!
>>
>> Unless there's a one-shot tracking the index pulses to determine
>> when the drive is up to speed - I'm not familier with this particular
>> controller so it may as you say not be an issue, however it's a
>> fairly major difference in the drives which has not been mentioned
>> before.

>I don't think the Altair controller is quite that smart. Since the
>disk starts spinning as soon as the door shuts I imagine it assumes
>that it is up to speed. I think the documentation talks about the
>Ready line in relation to seeks. The FD400 also used a stepper motor,
>so speed shouldn't ever be an issue as long as its ramped up.

I expect you are right - this is all pretty early/primitive stuff, but I
wanted you to be aware of the difference in case it does turn out
to be significant for whatever reason. The drives do turn at
different speeds which to my mind is a fairly major difference.


--
dave06a@ Low-cost firmware development tools: www.dunfield.com
dunfield. Classic computer collection: www.classiccmp.org/dunfield
com Some stuff I have for sale: www.dunfield.com/sale

> Grant, out of curiosity: which MITS/Altair floppy controller are you
> using? There were a number of models. Also, it may matter what
> software you are using. I don't recall all the details, but some of
> those controllers had an on board 8080 and its own code; some may have
> only used the S-100 CPU to run code. So, that controller may be
> smarter than you think.

The 88-DCDD set. The first ones used with Altair Basic and Altair
DOS.

> You posted earlier that you did not have all the docs. You probably
> know to look on my Web pages for MITS and Pertec docs and discussion
> of controllers and drives, at this Web link:

I have the manuals for the entire Altair Disk system, Tarbell,
Shugart, etc. I'm not sure which ones I was talking about.

> http://www.retrotechnology.com/herbs_stuff/drive.html

That page was pretty helpful and did point me in the right direction.

> You asked "for a conversation". Myself, I like to let the manuals do
> the "talking".

Sure. I've done that, but I still think its worth ironing out all the
details and finding out what other people have tried and found not to
work. Its also hard to make all of the mental connections being so
new to old disk drive theory. : )