[Question] 5.25 1.2mb disks on DOS 2.0?

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Fenix77
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[Question] 5.25 1.2mb disks on DOS 2.0?

Post by Fenix77 » Sun 14 Oct, 2018 11:44 pm

Hello

I found an old 5.25 1.2MB Basf floppy disk. The label say it is preformatted for DOS 2.0 and higher. The strange part is DOS 2.0 only can format 5.25 double density disks with one or two sides.

As far I know the support for 5.25 1.2Mb disk was added in DOS 3.0, the 3.5 720kb in DOS 3.2 ans 3.5 1440kb in DOS 3.3.

I also found that an 8' floppy disk existed and the 8' 2S/2D format had a capacity of 1.2MB and was supported in DOS 2.x https://en.wikipedia.org/wiki/Compariso ... ng_systems

So i guess if the disk had the same tracks and sectors it may be compatible
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SarahWalker
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Re: [Question] 5.25 1.2mb disks on DOS 2.0?

Post by SarahWalker » Mon 15 Oct, 2018 4:40 pm

No, BASF simply got the labeling wrong. Sometimes the simple answer is the correct one!

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omarsis81
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Re: [Question] 5.25 1.2mb disks on DOS 2.0?

Post by omarsis81 » Thu 18 Oct, 2018 6:05 pm

Fenix77 wrote:
Sun 14 Oct, 2018 11:44 pm
I also found that an 8' floppy disk existed and the 8' 2S/2D format had a capacity of 1.2MB and was supported in DOS 2.x
I have never seen an 8" floppy drive for PC

Zup
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Re: [Question] 5.25 1.2mb disks on DOS 2.0?

Post by Zup » Fri 19 Oct, 2018 5:21 am

Maybe is not related...

My ZX Spectrum +3 (a Z80 machine) had a 3 inch floppy drive (single sided, 180k/side) but can be fitted with 3.5 inch drives. +3DOS will format any disk to 180k, but (with the right tools) can use the whole 720k and plain +3DOS (was stored in ROM, so it can't be changed easily) would detect and use that 720k formatted disks (it reads the boot sector to find disk type, so even disks with 10 sectors/track could be used without changes to the OS).

So... could DOS 2.0 use 1.2Mb formatted disks (even if FORMAT.EXE doesn't support that format)?

Also, I know that DRIVER.SYS didn't exist in DOS 2.x but maybe some hardware vendor made drivers to make HD drives work with DOS 2.x?

Fenix77
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Re: [Question] 5.25 1.2mb disks on DOS 2.0?

Post by Fenix77 » Fri 19 Oct, 2018 3:03 pm

86-DOS, before was purchased by Microsoft, was compatible with Z80 machines. I have a 86-DOS working copy with an Altair Z80 emulator that support and boots off the 8' 1S/1D disk (one side/simple density disk, 250kb). ( I don't know if 86-DOS can be distribted free now)

So i think its not so strange that early DOS versions supported that format. According to Wikipedia ( I know it's information is not always accurate) MS-DOS 1.25 supported 8' 1S/1D 250 kb in addition to the 5.25 160/320kb.
DOS 2.0 added support for 8' disk with 500, 616 and 1232kb capacity, In addition, DOS 2.x supports 5.25 2S/2D disks formatted at 180kb/360kb and a single hard disk partition up to 16MB.
When IBM AT 286 was launched, it included DOS 3.0. In this version support for 5.25 1.2 mb 2S/HD disk was added and the 8' floppy disk was removed.
So later standard apps and even Winimage does not support the 8' floppy disks or disks images.

Zup
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Re: [Question] 5.25 1.2mb disks on DOS 2.0?

Post by Zup » Sat 20 Oct, 2018 6:40 am

On second thought, HD disks needs faster FDCs that maybe weren't supported in plain DOS 2.0, but I wonder it there existed a driver that could read HD floppies.

If the limit is imposed by the FDC (I mean, the routines that access the FDC) it have sense that the limit are DD disks, but DOS should be able to use 3.5 inch floppies (unless track number is hardcoded).

rliegh
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Re: [Question] 5.25 1.2mb disks on DOS 2.0?

Post by rliegh » Sun 21 Oct, 2018 5:48 pm

Fenix77 wrote:
Fri 19 Oct, 2018 3:03 pm
( I don't know if 86-DOS can be distribted free now)
It's on bitsavers, which is a hint -but only a hint. That's not the same as being explicitly made free. It does mean that it's unlikely that the BSA will kick down your door.

Also, a version of DOS 2 is there as well.

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