Subject: Re: Looking for schematics for DEC M702 and M720 modules

From: Al Kossow <[email-masked]>
Date: Mon Jun 9 21:10:01 2003

the M720 module schem is also on page 2-72 of volume II of the 8/I
maintenance manual
www.spies.com/aek/pdf/dec/pdp8/DEC-8I-HR2A-D_8Imaint_May70.pdf

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From: jamesd <[email-masked]>
Date: Mon Jun 9 21:22:01 2003

I I need a couple  3 1/2" diskette for an old 8086 six laptop too boot with 
... i don't have any good ones... if someone would like to offer to sell me 2 
or 3 for around  a buck apiece i would greatly appreciate it.. ebay only has 
them in 25 and 50 packs and i really don't even need 10 just one to boot and 
a backup... just going to use the laptop as a serial terminal 

I have a paypal account... if that makes it easier

James Dickens

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From: "Stuart Johnson" <[email-masked]>
Date: Mon Jun 9 21:31:00 2003

----- Original Message ----- 
From: "jamesd" <[email-masked]>
To: <[email-masked]>
Sent: Monday, June 09, 2003 9:20 PM
Subject: need 720k 3 1/2" disks

> I have a paypal account... if that makes it easier

Have you tried using a HD floppy and putting tape over BOTH sides of the
hole that marks the disk as HD? I should think that you could then format
the floppy as a 720 easily. I haven't tried this myself, but "Logic is the
art of going wrong - with confidence". I write enable factory-made read-only
1.44 floppies in this manner, and I use ordinary frosted "scotch" tape with
great success.

Stuart Johnson

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From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Mon Jun 9 21:51:00 2003

> > I I need a couple  3 1/2" diskette for an old 8086 six laptop too boot
> 1.44 floppies in this manner, and I use ordinary frosted "scotch" tape with

1) Many drives use a light and photocell to sense that hole.  At least use
an opaque tape!

2) Many 720K drives have no sensor for the "media ID" hole, so tape, etc
might turn out to be unnecessary unless/until you try to transfer files by
putting that diskette into your 1.4M drive.  However, there were some
drives (THANKS, Tony!) that use that same location for the "is there a
disk in the drive" sensor.

3) The magnetic coercivity is slightly different (600 for 720K, about 750
for 1.4M), so the result is not as reliable as using the right diskettes.
If it works OK, you should still keep looking for some of the correct
diskettes.

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From: "Stuart Johnson" <[email-masked]>
Date: Mon Jun 9 21:57:00 2003

----- Original Message ----- 
From: "Stuart Johnson" <[email-masked]>
To: <[email-masked]>
Sent: Monday, June 09, 2003 9:26 PM
Subject: Re: need 720k 3 1/2" disks

> with

I realize that answering one's own post isn't the best netiquette, but I
took time to try my suggestion and discovered that Windows XP Pro cannot
format a floppy EXCEPT as a 1.44. If you have a 720 floppy and need to
format it, you are SOL. This is in the XP documentation. This is an
IMPROVEMENT? :-(

Stuart Johnson

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From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Mon Jun 9 22:22:00 2003

> format it, you are SOL. This is in the XP documentation. This is an

It sucks.  We must all do whatever it takes to turn Bill Gates into a
millionaire.

But,...
I HAVE DONE IT.
Since I didn't have my copy of the "resource Kit", I didn't know that it
wasn't possible (The Wiley E. Coyote principle of software development)
If I were to have known that it wasn't possible, then it would have been a
lot more difficult.

XP dropped support of formatting 720K from the desktop, and from the
command line they dropped /F:720, and dropped /F:2.  But they did NOT
eliminate: 
FORMAT A: /T:80 /N:9

Note: I did it with a recent model Compaq; it is entirely possible that
the BIOS in some machines may pose other, additional problems.  And in
future service packs, they make fix the "error" of having left in the /T
and /N.

Hmmmm. Is SETVER still present in XP?  If so, then it would be possible to
use an older FORMAT without even having to patch it.

--
Grumpy Ol' Fred        [email-masked]

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From: "Stuart Johnson" <[email-masked]>
Date: Mon Jun 9 22:37:01 2003

----- Original Message ----- 
From: "Fred Cisin (XenoSoft)" <[email-masked]>
To: <[email-masked]>
Sent: Monday, June 09, 2003 10:17 PM
Subject: Re: need 720k 3 1/2" disks

> use an older FORMAT without even having to patch it.

Good! Thanks for the info.

Stuart Johnson

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From: Doc <[email-masked]>
Date: Mon Jun 9 22:44:01 2003

> command line they dropped /F:720, and dropped /F:2.  But they did NOT

   Darn you, Fred!
   Now I'll have to dig out that "advance" copy of Win2003 they sent me 
and install it on something, just to see.  I had noticed that the /F:720 
option was gone, but I have a DOS box that's on a lot more than the 
Windows box, so I never pursued it.  :)

	Doc

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From: jamesd <[email-masked]>
Date: Mon Jun 9 22:50:00 2003

> use an older FORMAT without even having to patch it.

hi

To answer your question a true DSDD 3 1/2" drive can't read a DSHD, because 
the media is differenent... so it can't read a disk formated in a DSHD 
drive... i can't even boot my laptop to test if the reverse is true. 

By the way i also have an excepted an offer from a fellow list member to send 
me disks... witch i really appreciate...   

James Dickens

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From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Mon Jun 9 23:12:01 2003

> the media is differenent... so it can't read a disk formated in a DSHD 
No, a "DSDD" can't read a DSHD because it is recorded at a higher density.
WHICH IS NOT THE DIRECTION THAT WE HAVE BEEN TALKING ABOUT!

The message that you just replied to was addressing the issue of whether
the 720K diskette could be formatted in an ordinary PC (specifically XP).

EVERY DSHD drive can read "DSDD" diskettes, so long as the disk controller
supports the lower (250K) data transfer rate, and the correct
software is present.  That includes every disk controller that you have
ever seen, although Tony and a few others may have some that were
originally designed for 8" that do not support the lower rates.

> me disks... witch i really appreciate...   

NO manufacturer of a 3.5" HD drive has ever made an HD drive that
couldn't ALSO handle the lower density.

Yes, the media is different.  The differences are: different chemical
coating to produce a slightly higher coercivity, and an extra hole in
the diskette to tell drives which diskette it is.  Those are the ONLY
differences.  NOTE: not all drives include the sensor to notice the disk
differences.

THEREFORE: as stated previously, the ability to FORMAT 720K in a 1.4M is
ONLY an issue of whether the SOFTWARE supports it, and if the harware is
"normal".

---

From: jamesd <[email-masked]>
Date: Mon Jun 9 23:36:00 2003

On Monday 09 June 2003 11:07 pm, Fred Cisin (XenoSoft) wrote:
> > To answer your question a true DSDD 3 1/2" drive can't read a DSHD,
> > because the media is differenent... so it can't read a disk formated in a
> > DSHD
>
my question was could  a DSHD disk formated using 720k parameters on a DSDD 
drive be readable on a DSDD drive was the question... i know a DSDD disk is 
readaple and formatable on a DSHD drive it just that a DSHD drive can't be 
fooled to write a usuable DSDD disk by covering the whole or any other 
message... because the media on the DSHD disk is different.. 

> > By the way i also have an excepted an offer from a fellow list member to
> > send me disks... witch i really appreciate...
>

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Tue Jun 10 00:16:00 2003

> message... because the media on the DSHD disk is different.. 

It is not VERY different.
YES, it WILL work.  It will produce a somewhat unreliable, but working
disk.  (600 v 750 oersted)  The media is different by less than 25% in
coercivity.  That is close enough that people who are not serious about
reliability will claim that it works "just fine".

In other words, in an emergency, you are likely to "get away with
it".  But use the correct diskette if there is any way to do so.  

In order to play with, or check out, the machine until you get some of the
correct diskettes, you CAN play with HD diskettes.   Just don't use them
for any data that you aren't willing to lose.

But your question also prompted discussion of HOW to "make do" with the
wrong diskette (tape, etc.) and the issue that XP doesn't make it easy to
format 720K (even with the right diskettes).

If you are still having problems finding real 720K's let me know; I can
certainly dig up a handful.  But I intend to hang onto the early
shutterless and manual shutter ones.

---

From: Eric Chomko <[email-masked]>
Date: Tue Jun 10 08:54:00 2003

> message... because the media on the DSHD disk is different..

I covered the hole of a preformatted 1.44mb DSHD diskette and put it
into
my Windows 2000 PC and tried to read it. It stated that the diskette was
not formatted, do I want to format it? Yes, I stated as a 720kb DSDD
diskette. It reformatted the diskette and showed the space at 720kb less
some overhead.
So on my system I could convert a 1.44mb floppy into a 720kb floppy
simply by covering the hole.

Do you need a boot disk (software) or do you need simply a formatted
720kb diskette?

Eric

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From: [email-masked] (Tony Duell)
Date: Tue Jun 10 19:13:21 2003

[DD 3.5" disks]
> hole that marks the disk as HD? I should think that you could then format

Didn't we go through this last week? The coercivity of the media is 
different between DD and HD disks (not very different in the case of 3.5" 
ones, but it's still different). 

I would think that in the case of 3.5" disks, you could format an HD disk 
as a DD one, but it will _not_ be reliable. It's the sort of thing you 
might have to do if DD disks become unobtainable (and then I might 
consider modifying the DD drive to increase the write current a bit), but 
while you can still easily get the right media, please use it...

-tony

---

From: [email-masked] (Tony Duell)
Date: Tue Jun 10 19:13:30 2003

> 1) Many drives use a light and photocell to sense that hole.  At least use

Strangly, every 3.5" drive I've worked on (and I've taken quite a few 
apart for repairs) have mechanical sensors. Either switches, or 
mechanincal 'flags' that work with slottted opto-switches. In the latter 
case, of coursem the light beam goes nowhere near the hole. 

I don't doubt that drives using optical sensors exist, but I can't think 
of one at the moment.

> disk in the drive" sensor.

Yes. The old Sony drives (used in the HP9121, to tie in another thread) 
have the disk-inserted sensor (which is a flag + slotted optoswitch in 
this unit) in exactly the same position as the HD hole. These drives will 
not recognise that an unmodified HD disk has been inserted.

-tony

---

From: [email-masked] (Tony Duell)
Date: Tue Jun 10 19:13:40 2003

> format a floppy EXCEPT as a 1.44. If you have a 720 floppy and need to

Do I conldue from this that LuseDoze XP doesn't support 5.25" drives at 
all? :-(

It's one thing to update defaults to correspond with the most commonly 
used media at the time of the OS's release, but to remove support for a 
device that some people may need seems to be ridiculous!

-tony

---

From: [email-masked] (Tony Duell)
Date: Tue Jun 10 19:13:50 2003

> originally designed for 8" that do not support the lower rates.

A _really_ obscure example, relating to 3.5" disks...

The original 3.5" drives rotated at 600rpm, and therefore transfered data 
twice as fast as the corresponding PC drives, which rotate at 300 rpm. 
Now by an amazing coincidence, this data rate is the same as the HD data 
rate for a PC drive.

So a controller for the original 3.5" drive should be able to handle a PC 
HD drive (same data rate) with the correct programming (it would be able 
to fit more sectors on a track than it could with the double-speed DD 
drive, and would have to not moan because of the longer wait for an index 
pulse). But this controller couldn't handle a DD disk in a normal PC drive...

-tony

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From: "Antonio Carlini" <[email-masked]>
Date: Wed Jun 11 02:25:01 2003

> Do I conldue from this that LuseDoze XP doesn't support 5.25" 

That seems a fair conclusion ... although I've been running XP
on a machine with a  5.25" drive in it and didn't notice until
right now :-) I have other machines with 5.25" drives so I 
suppose it's no great loss for me. Annoying though.

Antonio

-- 

---------------
Antonio Carlini             [email-masked]

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Wed Jun 11 11:33:11 2003

> Do I conldue from this that LuseDoze XP doesn't support 5.25" 
> drives at all? :-(

Just the FORMAT on the desktop.  The FORMAT at the command line still has
/T:x /N:y, but /F:z has been dropped to only "1.44"