Subject: 3.5" floppy drive in IBM XT?

From: Joe <[email-masked]>
Date: Mon Apr 7 17:15:00 2003

I picked up an old IBM XT today and it has a 3.5" floppy drive in it (and it works!) Anybody ever heard of this? The drive has it's own controller card and both it and the drive appear to be IBM parts. )I haven't pulled everything apart to be sure.)  FWIW the computer also has a FH 5 1/4" floppy drive and a HH 5 1/4" 10 Mb hard drive with a Seagate logo on the front of it. Anybody know if this is an original XT hard drive or a replacement drive? It's been so long since I've seen an original XT with the 10 Mb drive that I don't remember much about it.

   Joe

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Mon Apr 7 17:43:00 2003

On Mon, 7 Apr 2003, Joe wrote:
>   I picked up an old IBM XT today and it has a 3.5" floppy drive in it
> (and it works!) Anybody ever heard of this? 

Presumably, that is a 720K drive (subject to what the extra controller
is).  IBM sold internal and external 720Ks for the XT.  To do it their
way, you need PC-DOS 3.20 or newer, and need to do a DRIVER.SYS in
CONFIG.SYS.   But you could also use a 720K with certain OEM
(NON-IBM) versions of MS-DOS 2.11.

And the PC-JX (not available in U.S.) was available with 720K drives.

> The drive has it's own
> controller card and both it and the drive appear to be IBM parts. )I
> haven't pulled everything apart to be sure.)  FWIW the computer also

Do you mean that it is NOT connected to the same controller as the
5.25" drive?

> has a FH 5 1/4" floppy drive and a HH 5 1/4" 10 Mb hard drive with a
> Seagate logo on the front of it. Anybody know if this is an original
> XT hard drive or a replacement drive? It's been so long since I've
> seen an original XT with the 10 Mb drive that I don't remember much
> about it.
Which model Seagate?  It is likely to be an aftermarket drive.

--
Grumpy Ol' Fred        [email-masked]

---

From: "John Willis" <[email-masked]>
Date: Mon Apr 7 18:02:00 2003

Joe,

This is quite possible... Provided you have DOS 3.3+ and a controller with its own
BIOS extensions. I have an XT machine (actually it's an original PC) that works much the same way, although the drive is unusable as
I'm currently using DOS 3.21. As far as the hard drive goes, the original XT hard drive was a FH job with an IBM logo on the front
of it.

    John
+------------------------------------------------+--------------------------------+
| John P. Willis, MCP, SBI, NASA-STD-8739.5      | Coherent Logic Development     |
| Chief Executive Officer                        |  "Multiplatform Solutions      |
| Coherent Logic Development                     |    for a Multiplatform World"  |
+------------------------------------------------+--------------------------------+
| web: http://www.coherent-logic.com/                                             |
| e-mail: [email-masked]                                                  |
+---------------------------------------------------------------------------------+
----- Original Message -----
From: "Joe" <[email-masked]>
To: <[email-masked]>
Sent: Monday, April 07, 2003 6:12 PM
Subject: 3.5" floppy drive in IBM XT?

>   I picked up an old IBM XT today and it has a 3.5" floppy drive in it (and it works!) Anybody ever heard of this? The drive has
it's own controller card and both it and the drive appear to be IBM parts. )I haven't pulled everything apart to be sure.)  FWIW the
computer also has a FH 5 1/4" floppy drive and a HH 5 1/4" 10 Mb hard drive with a Seagate logo on the front of it. Anybody know if
this is an original XT hard drive or a replacement drive? It's been so long since I've seen an original XT with the 10 Mb drive that
I don't remember much about it.

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Mon Apr 7 18:17:01 2003

On Mon, 7 Apr 2003, John Willis wrote:
> Joe, This is quite possible... Provided you have DOS 3.3+ and a
> controller with its own BIOS extensions. I have an XT machine
> (actually it's an original PC) that works much the same way, although
> the drive is unusable as I'm currently using DOS 3.21. As far as the
> hard drive goes, the original XT hard drive was a FH job with an IBM
> logo on the front of it.

PC-DOS 3.30, BIOS extensions, and a different controller card are 
needed for a 1.4M drive, but NOT for 720K.  

720K uses same BIOS, same controller as 360K.  The only difference 
is how many tracks it has. PC-DOS 3.20 has full support for 720K 
drives in all models.

---

From: Joe <[email-masked]>
Date: Mon Apr 7 21:14:13 2003

>Do you mean that it is NOT connected to the same controller as the

   My mistake. It IS on the same controller. It didn't look like it till I got it apart.

>Which model Seagate?  It is likely to be an aftermarket drive.

     I expect that you're right. But it definitely appears to be connected an an IBM controller card. Interesting tidbit; the controller has BOTH data cables installed on it even though there's only one hard drive. The cables are stacked one on top of the other and taped together. I think this is the only time that I've ever seen a controller that came with two data cables.  

    FINALLY got the drive out! Two screws on the side (inside side, of course!) had backed out partially and jammed it up good. The drive is a ST 238R (32Mb) so it's definitely not an original drive.

      Joe

---

From: Patrick Finnegan <[email-masked]>
Date: Mon Apr 7 21:28:00 2003

On Mon, 7 Apr 2003, Joe wrote:

>      I expect that you're right. But it definitely appears to be
> connected an an IBM controller card. Interesting tidbit; the controller
> has BOTH data cables installed on it even though there's only one hard
> drive. The cables are stacked one on top of the other and taped
> together.  I think this is the only time that I've ever seen a
> controller that came with two data cables.

FWIW, All of the XTs and ATs I've taken apart have had both data cables
installed, and taped together like you said.

Pat
--
Purdue Universtiy ITAP/RCS
Information Technology at Purdue
Research Computing and Storage
http://www-rcd.cc.purdue.edu

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Mon Apr 7 22:52:00 2003

>    My mistake. It IS on the same controller. It didn't look like it till I got it apart.

Is it a 720K?  (look for a media sensor in the drive for a quick but not
certain test)   If so, then it has no need for any difference in cntroller
or BIOS than a 360K.

> connected an an IBM controller card. Interesting tidbit; the
> controller has BOTH data cables installed on it even though there's
> only one hard drive. The cables are stacked one on top of the other
> and taped together. I think this is the only time that I've ever seen
> a controller that came with two data cables.

Yeah, IBM always did that (taping the cables together, prefolded to fit
tidily in the case)  That tape is prbably pretty thoroughly decayed by
now.

>     FINALLY got the drive out! Two screws on the side (inside side, of
> course!) had backed out partially and jammed it up good. The drive is
> a ST 238R (32Mb) so it's definitely not an original drive.

I think that the R means that it is rated for RLL use.
The original stock IBM hard drive controller came set for 10M, but could
be jumpered (solder jumpers or put in a dipswitch) for IIRC, 5M, 10M, 16M,
26M?

Minor bad news: on the XT (not AT), there were incompatabilities between
different controllers, so the drive needs to be reformatted to switch to a
different brand of controller!

---

From: "Curt vendel" <[email-masked]>
Date: Mon Apr 7 23:44:08 2003

Joe,

   Wow, major flashbacks!!!   I remember installing my 1st 3.5" into an AT,
not XT but I do recall there was a big routine that we had to go through to
install a bunch of drivers and such to allow the system to recognize and use
the 3.5" disk drive.

Curt

----- Original Message -----
From: "Joe" <[email-masked]>
To: <[email-masked]>
Sent: Monday, April 07, 2003 6:12 PM
Subject: 3.5" floppy drive in IBM XT?

>   I picked up an old IBM XT today and it has a 3.5" floppy drive in it
(and it works!) Anybody ever heard of this? The drive has it's own
controller card and both it and the drive appear to be IBM parts. )I haven't
pulled everything apart to be sure.)  FWIW the computer also has a FH 5 1/4"
floppy drive and a HH 5 1/4" 10 Mb hard drive with a Seagate logo on the
front of it. Anybody know if this is an original XT hard drive or a
replacement drive? It's been so long since I've seen an original XT with the
10 Mb drive that I don't remember much about it.

---

From: Don Maslin <[email-masked]>
Date: Tue Apr 8 00:50:01 2003

On Mon, 7 Apr 2003, Joe wrote:

>     FINALLY got the drive out! Two screws on the side (inside side,
> of course!) had backed out partially and jammed it up good. The
> drive is a ST 238R (32Mb) so it's definitely not an original
> drive.

Interesting question is whether it is being used as a 21mb MFM
drive or as a 33mb RLL.  My guess would be 21mb.

						- don

---

From: Joe <[email-masked]>
Date: Tue Apr 8 07:27:01 2003

>drive or as a 33mb RLL.  My guess would be 21mb.

     It's an RLL drive and is 32 Mb according to my sources.

     Joe

---

From: Ethan Dicks <[email-masked]>
Date: Tue Apr 8 10:13:00 2003

>      It's an RLL drive and is 32 Mb according to my sources.

Does that mean that you confirmed that your controller is an RLL
controller?  There's no substantial difference between an ST-238R
and an ST-225 except a) the label, and b) some manufacturing confidence
that a tighter encoding scheme will not drop bits.

The data cable holds analog signals.  This is significantly different
than an IDE drive (whose cable is all digital).  The density of storage
is entirely dependent on the nature of the controller.  The quality
of retention is dependent on the nature of the drive.

People did attempt to stick an ST-225 on an RLL controller.  Results
were mixed.  It was a "cheap" way to increase storage 50%, but if
your drive had some weak spots, you would develop lots of data errors.

Others chose to put ST-238Rs on MFM controllers.  Results there were
much better.  You only got 21.4MB of storage (marketing MB, AFAIK),
but you weren't taxing the surface as much as Seagate said you could.

So, yes, your sources are correct - the ST-238R *does* do 32MB, but
only when attached to an RLL controller (which you might very well have).

-ethan

P.S. - there were other arrangements than 614 x 4 x 17 when ST-506/ST-412
drives were used in non-PeeCee applications.  One that immediately comes
to mind is the Tandon drive (TM602S or TM603S) used in the Commodore
D9060 and D9090 IEEE-488 hard drives.  Due to the nature of Commodore
"DOS" and its floppy origins, they chose not to change the block size
of 256 bytes per block.  Its internal OMTI controller did tracks of
32 sectors of 256 bytes for a total of 8192 bytes per track, not
8704 (17 x 512).  Yes, to keep it on topic, the ST-225 will work in a
D9060, but will only use the first 154 tracks).

(see http://www.softwolves.pp.se/misc/arkiv/cbm-hackers/2/2264.html ,
among other things you can find googling for D9090)

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Tue Apr 8 12:32:00 2003

>      It's an RLL drive and is 32 Mb according to my sources.

But what controller is it connected to?
The IBM controller (full length, made by Xebec) was MFM.  ONLY.
When connected to an MFM controller, the drive will only be usable for 2/3
of its rated RLL capacity, giving you a very good 20M drive.

MFM and RLL gave two different recording encodings on what was otherwise
an identical drive.  But many/most? MFM drives could not reliably handle
the higher "density" of RLL.  Drives that were sold as RLL could.

---

From: Don Maslin <[email-masked]>
Date: Tue Apr 8 13:21:01 2003

>      It's an RLL drive and is 32 Mb according to my sources.

My curiousity was really as to the controller and whether it was
RLL or MFM, Joe.
						- don

---

From: Joe <[email-masked]>
Date: Tue Apr 8 16:23:00 2003

At 08:10 AM 4/8/03 -0700, you wrote:
>controller? 

   No, my controller is an original IBM 10 Mb MFM HD controller. It's only using 10 Mb of the drive.

   Joe

---

From: Joe <[email-masked]>
Date: Tue Apr 8 16:23:47 2003

Don,

  The controller is full length and has XEBEC chips and a Z-80 CPU. I'm sure that it's MFM. It's marked IBM and next to that is a paper sticker that says #1501492. Also marked IBM 6135984 in copper foil. My diagnostic tool shows four settings in the ROM, the 10Mb drive is third setting. I didn't look at the capacity of the other settings. It's running this drive as a 10 Mb MFM drive but the drive is rated as a 32Mb RLL capable drive.

     Joe

---

From: "Fred Cisin (XenoSoft)" <[email-masked]>
Date: Tue Apr 8 16:52:00 2003

On Tue, 8 Apr 2003, Joe wrote:

>   The controller is full length and has XEBEC chips and a Z-80 CPU.
> I'm sure that it's MFM. It's marked IBM and next to that is a paper
> sticker that says #1501492. Also marked IBM 6135984 in copper foil. My
> diagnostic tool shows four settings in the ROM, the 10Mb drive is
> third setting. I didn't look at the capacity of the other settings.
> It's running this drive as a 10 Mb MFM drive but the drive is rated as
> a 32Mb RLL capable drive.

> my controller is an original IBM 10 Mb MFM HD controller. It's only
> using 10 Mb of the drive.

Near the middle of the board are 8 solder pads.  By jumpering those (they
are the right size for a 4 position dip switch), you can get the
controller to use the other setting that are in its ROM.  The 4 positions
are 2 for each drive, resulting in 4 possible combinations for each
drive.  10M, the default, is both switches open.

OR, there are software ways tio override the controller - 
check with Steve Thatcher.

---

From: [email-masked] (Tony Duell)
Date: Tue Apr 8 17:19:01 2003

>      It's an RLL drive and is 32 Mb according to my sources.

All that means is the drive is capable of handling RLL encoding 
(basically, it can correctly reproduce pulses at half-multiples of the 
MFM spacing (although they won't ever be closer together than 
the MFM encoder would produce).  Such a drive will, of course, work 
correctly with an MFM controller, but will have a lower capacity when so 
used (in this case 21 Mbytes).

Remember that with the ST506/ST412 interface, it's the _controller_, not 
the drive that handles the data encoding/decoding. The 'data cable' 
carries the raw data stream to/from the disk.

-tony

---

From: [email-masked] (Tony Duell)
Date: Tue Apr 8 17:19:07 2003

> The data cable holds analog signals.  This is significantly different

Actually, all the signals on the data cable are digital. The Read/Write 
data signals are differential pairs of similar-to-TTL level signals, 
normally using a 26LS31 driver and 26LS32 receiver.

But in a sense they're analogue in _time_. In write mode, the drive 
writes a flux transition to the disk for every pulse on the write data 
line. In read mode, the drive sends a pulse on the read data line for 
every flux transition on the disk. There are some restrictions on 
allowable frequencies of transisitions, of course.

Therefore it's up to the controller to handle the raw data from the disk, 
to sort it out into sectors, check the sector headers and checksums, and 
so on. And when writing, the controller has to pack the user's data into 
sectors, add the correct headers, etc. The choice of encoding scheme 
(FM/MFM/RLL) is up to the controller. 

RLL drives should really be called RLL _capable_ drives. They are capable 
of handling the somewhat tighter timing requirements of the RLL encoding 
scheme. They'll work fine with MFM encoding too (just as double-denisty 
-- MFM -- floppy disks will work on a single density -- FM -- controller).

-tony

---

From: Joe <[email-masked]>
Date: Tue Apr 8 20:13:00 2003

Thanks for the info but I don't see the pads that you're talking about. Near the center of the card are pads for a 14 pin DIP with nothing strapped. It's unlabeled but is located between ICs 8D and 10D.  Right next to the bracket on the very end of the card is a place for an 8 pin DIP. It has the package outline painted on the board. But it has two rows on header pins installed instead of a DIP package. (The rows are .4" apart.) One row of pins is marked S1 and the other is marked 1, 2, 3, 4. There's nothing jumpered on it either but I suspect that it's used to select the drive sizes.

   Joe

---

From: Tothwolf <[email-masked]>
Date: Tue Apr 8 21:16:00 2003

On Tue, 8 Apr 2003, Joe wrote:
> > Near the middle of the board are 8 solder pads.  By jumpering those
> > (they are the right size for a 4 position dip switch), you can get the
> > controller to use the other setting that are in its ROM.  The 4
> > positions are 2 for each drive, resulting in 4 possible combinations
> > for each drive.  10M, the default, is both switches open.
>
> Thanks for the info but I don't see the pads that you're talking about.
> Near the center of the card are pads for a 14 pin DIP with nothing
> strapped. It's unlabeled but is located between ICs 8D and 10D.  Right
> next to the bracket on the very end of the card is a place for an 8 pin
> DIP. It has the package outline painted on the board. But it has two
> rows on header pins installed instead of a DIP package. (The rows are
> .4" apart.) One row of pins is marked S1 and the other is marked 1, 2,
> 3, 4. There's nothing jumpered on it either but I suspect that it's used
> to select the drive sizes.

The 8 pin dip outline near the bracket is what you are looking for. I've
seen WD boards with empty pads, a 4 position dip switch, an empty socket,
and a socket with a punch-type shunt installed. I used to just plug a
standard 4 position dip switch into the header/socket to make selecting
the various drive types much simpler.

-Toth