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Great Hierophant
February 6th, 2009, 02:25 PM
Has anyone had experience with these? I mean 5.25 and 3.5 combos. Apparently they are considered one drive, not two because they have one connector. Does that mean you have to change the drive designation in the BIOS every time you wished to use the other drive? Or do they do the "twist" on their motherboard? Do they need drivers outside the OS?

Druid6900
February 6th, 2009, 02:54 PM
The ones I have plug in (on the A: connector) and are seen as drive A: and B: and work as such.

No drivers seem to be needed and the only time you have to fiddle with anything is if, say, you have the 3.5 as A: and the 5.25 as B: and you want to switch the order. This is, usually, accomplished with a jumper block on the drive logic board

patscc
February 6th, 2009, 03:17 PM
They do the 'cable twist' bit internally, so your computer sees 2 drives. They're only considered one drive because they only take up one bay. The rest as Druid6900 said.
patscc

Fallo
February 6th, 2009, 03:54 PM
No drivers seem to be needed and the only time you have to fiddle with anything is if, say, you have the 3.5 as A: and the 5.25 as B: and you want to switch the order. This is, usually, accomplished with a jumper block on the drive logic board

I've got a Panasonic combo drive in my Pentium. The computer has a BIOS setting to select which floppy is A: and which is B:, so I don't have to set jumpers on the drive.

Chuck(G)
February 6th, 2009, 04:39 PM
That works for BIOS-access programs, but for programs that directly access the FDC hardware, the swap isn't done, so you have to be careful.

On my Teac drives, there are two jumper positions to set either drive to A or B. Easy.

I don't care for the combo drives except for casual use-you pay a price for the slim design in mechanical ruggedness. But I do use them more than I care to admit.

Druid6900
February 6th, 2009, 08:05 PM
I don't use them in my primary computers, but, every one of my PC test jigs has one attached because it's more convenient than having two drives hanging off each one. Fortunately, I lucked into a whole box of them from somewhere.

Fallo
February 6th, 2009, 08:17 PM
That works for BIOS-access programs, but for programs that directly access the FDC hardware, the swap isn't done, so you have to be careful.

True, but hardly anything accesses the floppy controller directly, so it's not a big problem. I believe that my drive is jumpered to use the 3.5" floppy as A:, which is normally how I have it set in the BIOS.


I don't care for the combo drives except for casual use-you pay a price for the slim design in mechanical ruggedness. But I do use them more than I care to admit.

I suppose combo drives might be an easy way of adding a 3.5" floppy to an XT. Since they use an edge connector, you could use the XT's original floppy cable (which didn't have the header connectors used by 3.5" drives).

Druid6900
February 6th, 2009, 08:23 PM
I suppose combo drives might be an easy way of adding a 3.5" floppy to an XT. Since they use an edge connector, you could use the XT's original floppy cable (which didn't have the header connectors used by 3.5" drives).

None of mine do, they all use pin-headers. Guess they are a later model although I've never actually seen one using a card edge connector.

Fallo
February 6th, 2009, 09:31 PM
None of mine do, they all use pin-headers. Guess they are a later model although I've never actually seen one using a card edge connector.

Whoops, my combo drive is an Epson, not a Panasonic (just checked). Specifically, it's an Epson SD-800. I did some research on this drive, and evidently the early ones (like mine) had edge connectors, and later ones had headers.

Chuck(G)
February 6th, 2009, 09:31 PM
All of my Teac FD-505s have pin headers--which makes sense, if you consider that this is post 3.5" material. All of the ones that I have are 1.2M-1.44M units, which means that they're not going to work so well on a stock XT, as the XT controller supports only 250Kbps data rate. You could use a third-party floppy controller, but then you might as well use standard drives.

I don't recall if the 505 was ever made with a 360K 5.25" drive.

Anyone imaging "alien" diskette formats for other systems will be dealing with direct controller access. None of those people here, are there? :)

NeXT
February 6th, 2009, 09:48 PM
My Epson combo drive simply has an internal ribbon cable that links the two drives to the connector on the back. It sure is nice saving a drive bay for something else but if you are like me, your newer BIOS will only allow you to use one of the two drives even though the board and controller is pinned and wired to support two (WTF were you thinking MSI? :machinegun: )
Still, in most cases it's just a slimline laptop 3 1/2" floppy drive screwed and wired to the top of a 5 1/4" floppy drive.

Fallo
February 6th, 2009, 10:38 PM
All of my Teac FD-505s have pin headers--which makes sense, if you consider that this is post 3.5" material. All of the ones that I have are 1.2M-1.44M units, which means that they're not going to work so well on a stock XT, as the XT controller supports only 250Kbps data rate. You could use a third-party floppy controller, but then you might as well use standard drives.

Well yeah, you'd have to use them as double-density drives.


Anyone imaging "alien" diskette formats for other systems will be dealing with direct controller access. None of those people here, are there? :)

That would only be a problem if you're trying to write disks for stuff like the TRS-80 or Atari 8-bit.

Chuck(G)
February 6th, 2009, 10:54 PM
Well yeah, you'd have to use them as double-density drives..

Nope, not even. The 1.2MB drive in an FD505 spins at 360 RPM, necessitating a 300kbps data clock--and it's 96tpi to boot, so there's not even BIOS support for double-stepping it to handle 48 tpi double-density formats.

Some other 1.2MB drives can be jumpered to be dual-speed so that in low-density mode, the floppy spins at 300 RPM. But not the 505--and that still doesn't handle the double-step requirement.

modem7
February 7th, 2009, 12:08 AM
and it's 96tpi to boot, so there's not even BIOS support for double-stepping it to handle 48 tpi double-density formats.
The 01/10/86 revision BIOS for the IBM 5160 introduced support for the 1.2MB drive in the 5160, including 360KB media in the drive.
There are references to double-stepping in the source code.

Great Hierophant
February 7th, 2009, 07:37 AM
Whoops, my combo drive is an Epson, not a Panasonic (just checked). Specifically, it's an Epson SD-800. I did some research on this drive, and evidently the early ones (like mine) had edge connectors, and later ones had headers.

That is the one I got, an Epson with an edge connector. Fortunately I have a edge/pin ribbon with a pin connector on the motherboard side.

I think my motherboard will support two disk drives, the BIOS talks about A: and B:.

Chuck(G)
February 7th, 2009, 08:15 AM
The 01/10/86 revision BIOS for the IBM 5160 introduced support for the 1.2MB drive in the 5160, including 360KB media in the drive.
There are references to double-stepping in the source code.

Yes, but you still need a capable controller (500Kbps and 300Kpbs in addition to 250Kbps), no? Most 5160s don't have it.

amouse
February 7th, 2009, 08:36 AM
I'll just add the unfortunate fact that on some modern motherboards only 1 floppy drive is supported.

So when I finally got a combo drive I put it into my "modern server" to be able to transfer both 3.5 and 5 inch diskette formats only to find out that only the A: was visible.

How annoying! So I've moved the drive to an older "target" system.

regards mb.

Chuck(G)
February 7th, 2009, 08:49 AM
I'll just add the unfortunate fact that on some modern motherboards only 1 floppy drive is supported.

So when I finally got a combo drive I put it into my "modern server" to be able to transfer both 3.5 and 5 inch diskette formats only to find out that only the A: was visible.

How annoying! So I've moved the drive to an older "target" system.


Another interesting variation that I've seen on some Compaq Deskpros is that the "straight" part of the cable goes to drive A: while the twisted part goes to drive B: (no BIOS swapping involved; this is the way the darned thing's wired). I imagine that this was because such systems normally shipped with a single floppy drive and an untwisted cable was simply less expensive to make.

vwestlife
February 7th, 2009, 09:32 AM
I'll just add the unfortunate fact that on some modern motherboards only 1 floppy drive is supported.

So when I finally got a combo drive I put it into my "modern server" to be able to transfer both 3.5 and 5 inch diskette formats only to find out that only the A: was visible.
My Gateway Athlon machine is like that. It has an open 5" drive bay, but no support for a second floppy drive. And with no ISA slots, I can't put in an aftermarket floppy controller, either!

Right now I'm using my old 5x86 computer to transfer data from my old 5" disks. With a Cyrix 5x86-120 set to run in clock-quadrupled 133 MHz mode (undocumented but working fine!) it makes an excellent DOS/Windows 3.x machine.

Fallo
February 7th, 2009, 12:42 PM
If the BIOS performs double-stepping, then that would mean those programs you mentioned that access the controller directly would not work on a 1.2MB drive (when using 360k disks).

Aside from programs that write TRS-80 and such disks, a few utilities such as sector editors might perform direct controller access. I also know of at least one game, Dunzhin: Warrior of Ras, that does it.

Now my Pentium still has it's original 3.5" floppy in it. I'm not using it at the moment, but I found that if you connect it, you can use it alongside one of the combo's two drives (either the 3.5" or 5.25"; you can't use them both at the same time if there's another drive on the cable).

My idea was that you could simply use the combo's 3.5" drive in an XT this way. Of course, for it to work, you'd have to have a second floppy in the XT to prevent it from trying to use the 1.2MB drive.

One other thing I'm curious about. The later XTs were apparently available with internal 3.5" floppies. I've seen pictures of this setup; the drives were black and had a blue eject button. IBM must have used a different floppy controller in those XTs.

modem7
February 7th, 2009, 02:23 PM
If the BIOS performs double-stepping, then that would mean those programs you mentioned that access the controller directly would not work on a 1.2MB drive (when using 360k disks).
Such a program (just like the code in the BIOS) can establish if a formatted 360K floppy is inserted in a 1.2M drive, and in that case do the double stepping itself.


One other thing I'm curious about. The later XTs were apparently available with internal 3.5" floppies. I've seen pictures of this setup; the drives were black and had a blue eject button. IBM must have used a different floppy controller in those XTs.
The 5160 section of Mueller's Upgrading & Repairing PCs (first edition) includes, "A recent option is a 3.5 inch 720K floppy disk drive. The 3.5 inch drives are available in a normal internal configuration or as an external device." And so being 720K drives, the 'normal' controller could be retained.

Chuck(G)
February 7th, 2009, 03:13 PM
Now my Pentium still has it's original 3.5" floppy in it. I'm not using it at the moment, but I found that if you connect it, you can use it alongside one of the combo's two drives (either the 3.5" or 5.25"; you can't use them both at the same time if there's another drive on the cable).

My idea was that you could simply use the combo's 3.5" drive in an XT this way. Of course, for it to work, you'd have to have a second floppy in the XT to prevent it from trying to use the 1.2MB drive.

One other thing I'm curious about. The later XTs were apparently available with internal 3.5" floppies. I've seen pictures of this setup; the drives were black and had a blue eject button. IBM must have used a different floppy controller in those XTs.

As Modem7 has pointed out, the 720K format is nothing more than the 360K format with 40 added cylinders; same data rate. 1.2MB drives, however, are a whole different affair--mostly being descended from 8" drives (360 RPM, 500Mbps data rate). In fact, the NEC 9801 series smoothly progressed through 8" to 5.25" to 3.5" 360 RPM drives without any major changes to software--the capacity is exactly the same on all drives.

Leave it to the USA to do things in the "let a hundred flowers bloom" way with the PC platform.

Back in the 80's, there was a gizmo (I don't recall what it was called offhand) that was an ISA plug-in switch board that allowed you to take a 2-floppy system and support 4 floppies without changing the controller out. Perhaps a manual switch could be rigged for your setup.

Fallo
February 7th, 2009, 03:16 PM
The 5160 section of Mueller's Upgrading & Repairing PCs (first edition) includes, "A recent option is a 3.5 inch 720K floppy disk drive. The 3.5 inch drives are available in a normal internal configuration or as an external device." And so being 720K drives, the 'normal' controller could be retained.

Ok, I found out the details. The internal 3.5" drives that were offered in late XTs (and ATs) were made by Alps, and they had edge connectors.

Great Hierophant
February 10th, 2009, 06:44 AM
This combo drive is the Epson SD-880, and it is composed of bolting two slimline drives together. The two drives are connected by a thin ribbon cable, which is twisted. There is a jumper on the circuit board to select which drive is A: and B:. You can also do the selection by changing which connector on a two-connector floppy drive cable is fitted to the card edge.

Interestingly, it also has a jumper to set the rotational speed of the 5.25 drive from 360K to 300K.

http://groups.google.com/group/comp.periphs/browse_frm/thread/162bc49e81f10e76?hl=en&ie=UTF-8&q=Epson+SD-880+jumpers

Chuck(G)
February 10th, 2009, 09:36 AM
Wish I would have know about those 18 years ago when I had to provide a bunch of combo drives that would handle 1.3MB 5.25" and 3.5" floppies. I did discover a trace that could be jumpered on the Teac 505, but it wasn't easy.