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PC 5.25 Floppy questions (Was: A few questions

B

bbcmicro

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Here are some general questions;
1) Is a DD 5.25" disk used in 360kb drives, and is there a HD for 1.2mb?
2) Is 360kb on a DD DS disk 360k on each or in total?
3) Anyone know where I can find any information about the 4 DIP switches on the back of my XT clone? I want to know what they do.
4) Does the XT support 1.2mb drives, and is it likely my clone will?
 
I'll try to answer what I can.
bbcmicro said:
1) Is a DD 5.25" disk used in 360kb drives, and is there a HD for 1.2mb??
Click to expand...

For the PC family of computers there were two MAIN formats for the 5.25" drives. On XT and earlier, there were DS/DD drives (and SS varients) that supported up to a total of 360k per disk. On AT and later, there was DS/HD, which supported 1.2m per 5/25" disk.

For the pedants, I know there was also the 160/180k single sided formats and the 320k double sided formats. I think there were several others, including the DS/QD (720K 5.25") e.g. Tandy 2000, but I'm trying not to be too confusing.

See: http://www.apple2.org.za/mirrors/ground.icaen.uiowa.edu/MiscInfo/Misc/diskfmts for some great floppy format details. Those marked (3) were PC, (4) were introduced in AT and later.
bbcmicro said:
2) Is 360kb on a DD DS disk 360k on each or in total?
Click to expand...
Not sure what you're asking. Each diskette held 360k total, or 180k per side.

bbcmicro said:
3) Anyone know where I can find any information about the 4 DIP switches on the back of my XT clone? I want to know what they do.
Click to expand...
See if the board is listed at: http://www.resoo.org/docs/_hardware/th99/m/m8088_1.htm
Don't just search by name, but look at the different board layouts.

bbcmicro said:
4) Does the XT support 1.2mb drives, and is it likely my clone will?
Click to expand...
Not natively. There are add on cards that support 1.2mb and 1.4mb drives in XT class machines. These have their own bios. These are still available from http://www.jdr.com/interact/item.asp?itemno=MCT-FDC-HD4
I have several of these in my duplication machines at home to support different formats.
 
DIP switches

DIP switches

bbcmicro said:
3) Anyone know where I can find any information about the 4 DIP switches on the back of my XT clone? I want to know what they do.
Click to expand...

Out of curiosity, would you tell me BBC where those DIP switches are
exactly located, on the motherboard or...?
 
If you are facing the front of the computer, upper left near/under(?) the PSU poking out the back panel.
 
I assume those DIP switches would be for the graphics - my Epson AX2e has a similar setup.

Are they on a card/mainboard/etc?
 
Not every question about floppy drives is a PC question. But this question clearly is very targeted at PCs, as I know of no other machine that used 1.2MB 5.25 inch drives. So I'm moving the thread to PCs.

Also, subjects need to be more descriptive than just 'A few questions'.
 
mbbrutman said:
I know of no other machine that used 1.2MB 5.25 inch drives.
Click to expand...
Several of my TRS-80 model 12, 16, 16b, 6000s have 1.2MB 5.25 inch drives retrofitted :)
However, based on bbcmicro's posting history, I too assumed this was about PC/XT/AT/PS-2 drives.

mbbrutman said:
Also, subjects need to be more descriptive than just 'A few questions'.
Click to expand...
Crack that whip!! ;-) (note the winky)
 
Attempt at humor duly noted.

How did those machines take the 1.2MB drives? Are they just treating them as conventional 40 track drives, or did you upgrade their controllers and software to handle the higher data rates and extra tracks?
 
The 5.25" HD drive is almost electrically identical to the 8" DS/DD drive. No upgrade or modification to the system itself is required.

Making an adapter based either on fdadap, Dave Dunfields notes, or using Frank Durda's information, you can simply replace MOST 8" drive installations with a 5.25" HD drive.

See:
http://www.dbit.com/fdadap.html
http://www.classiccmp.org/dunfield/img/cnct.htm
http://nemesis.lonestar.org/computers/tandy/hardware/model16_6000/floppyfix.html

For notes on doing this.

It just requires a switch, a soldering iron and a little patience. Someone also sent me an express PCB layout for making these adapters. $59 plus shipping give you 3 adapter PCBs.

Dave Dunfield's ImageDisk is a great program for archiving soft sectored folppies.
 
I've used a similar trick to run 1.44MB drives on old machines designed for 720K floppies. But in this case, you're not really using it as a 1.2MB drive ... it might as well be a 360K drive. To get the features of a 1.2MB drive you'd have to increase the controller's data rate and tell the machine how to use the extra tracks, right?
 
Nope, you're using it as a 1.2MB drive. The tandy 12/16/6000 series uses 77 tracks, 2 sides, 16 sectors per track, 512 bytes per sector for a total storage of (((76x2x16)+16)x512 = 1,253,376 bytes (Track 0 is single sided)

See the following entries from the drive table I pointed to http://www.apple2.org.za/mirrors/ground.icaen.uiowa.edu/MiscInfo/Misc/diskfmts :
HTML: 
disk	speed		data rate	trk	sector	trk/hd
size	rpm	s/rev	kb/s	scheme	kb	cnt*sz	count	KB
--------------------------------------------------------------------------------
8"	360	0.167	500	MFM	83.33	26*256	77/2	1040	DSDD
5.25"	360	0.167	500	MFM	83.33	15*512	80/2	1200	DSHD
 
Last edited:
Nice. I wasn't aware of anybody storing that much data on an 8" diskette. The data rate and RPMs match perfectly ...
 
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