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Booting 720K in the 5150

G

Great Hierophant

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I know that the IBM PC 5150 does not have BIOS support for 720K disks or their drives. Using DOS's DRIVER.SYS, support can be easily added as of DOS 3.2 or above. However, what would happen if a 720K disk tried to boot? Also, what about those 720K disks that do not use DOS natively to boot (i.e. booters). Would they load their own support for 720K and boot?
 
Great Hierophant said:
I know that the IBM PC 5150 does not have BIOS support for 720K disks or their drives. Using DOS's DRIVER.SYS, support can be easily added as of DOS 3.2 or above. However, what would happen if a 720K disk tried to boot? Also, what about those 720K disks that do not use DOS natively to boot (i.e. booters). Would they load their own support for 720K and boot?
Click to expand...

I think it would have tried to boot it as a 360Kb disk. The big question would have been the disk controller. I'm not sure if 720Kb 3.5" disk drives does use the same transfer rates as the 360Kb 5.25" disk drive.

However, if it does boot, it'll manage to boot at least the first sector, but if the boot code request the BIOS to read beyond sector 40, it's likely to fail.
 
Why can't ya boys just leave the 5150 alone the way it was ment to be, If you want VGA 760KB floppys Model M's then go find an collect a PS/2.

I don't understand why take something that is historical and mod the shit out of if, upgrade it like it still was in use in the late 1980s?
Sorry if it piss's anyone off, I just don't understand!




Great Hierophant said:
I know that the IBM PC 5150 does not have BIOS support for 720K disks or their drives. Using DOS's DRIVER.SYS, support can be easily added as of DOS 3.2 or above. However, what would happen if a 720K disk tried to boot? Also, what about those 720K disks that do not use DOS natively to boot (i.e. booters). Would they load their own support for 720K and boot?
Click to expand...
 
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frozenfire75i said:
Why can't ya boys just leave the 5150 alone the way it was ment to be, If you want VGA 760KB floppys Model M's then go find an collect a PS/2.

I don't understand why take something that is historical and mod the shit out if upgrade it like it still was in use in the late 1980s?
Click to expand...

He didn't say he was actually going to do it, he is just asking what'll happen if sombody did it.

I think that wat people do with their 5150 PC's is up to the owner. It's their computer and if they decides to alter it, it's their cause. As long as nobody (force me to) alter my system.
 
frozenfire75i said:
Yes I totally agree, but that's not what I am asking, I am asking why?
Click to expand...

My reason is that I have images of booters that were released on 360K and 720K disks, but I only have the 720K version. I would like to know if there is any likelihood of their working at all. I would hope that they would bypass the BIOS and use their own routines to read past sector 40.
 
Great Hierophant said:
My reason is that I have images of booters that were released on 360K and 720K disks, but I only have the 720K version. I would like to know if there is any likelihood of their working at all. I would hope that they would bypass the BIOS and use their own routines to read past sector 40.
Click to expand...

It is acutslly possible to write a 360Kb image to a 720Kb disk. This is because it's using the same number of sectors per track and number of heads. It wouldn't surprise me if the 720Kb booters only use the first half of the tracks.

Give it a try and see what it does.
 
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hex editor

hex editor

Maybe load the disk into a hex editor and see if there's even any data past track 40.
If it came on 1 360k originally, I'd be surprised if there was more data on the 720, unless they added features.
patscc
 
It works just fine--my first 5150 had a 720K 5.25" drive as the first drive (I moved the 360K to the B: slot).

Look, the track format's the same (8/9 x 512); the rotational rate's the same (300 RPM)--the BIOS doesn't put limits on cylinder number (40 vs. 80). Essentially, a 720K drive appears as a 360K drive with double the number of cylinders. After that, it all depends on what version of DOS you're using.

What I don't recall is if PC-DOS 1.1 actually had a FAT ID byte for 720K--I'll have to check.

<curmudgeon>
It'd actually be more interesting if some of the people who were after an authentic 5150 experience actually ran DOS 1.1 instead of a later version.
</curmudgeon>
 
Great Hierophant said:
I know that the IBM PC 5150 does not have BIOS support for 720K disks or their drives. Using DOS's DRIVER.SYS, support can be easily added as of DOS 3.2 or above. However, what would happen if a 720K disk tried to boot? Also, what about those 720K disks that do not use DOS natively to boot (i.e. booters). Would they load their own support for 720K and boot?
Click to expand...

You can get an 8-bit Floppy Card that will work with 1.44 and 720k floppies, as well as the old 360 and 1.2 meg floppy drives.

I remember back when I actually owned an XT, and the 720k drives came out, I had to use driveparm to get the thing to work, by the time cards came out that directly support 720k and 1.44 meg drives, I moved onto the 286 level of computers.

My 5150 currently has the 2 360k drives, so it appears at it was released.

Inside it has an 8bit VGA card that connects to a IBM VGA monitor, I currently don't own a CGA or Monochrome monitor for it...getting one in half decent shape is not easy.

:>
 
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gerrydoire said:
I remember back when I actually owned an XT, and the 720k drives came out, I had to use driveparm to get the thing to work, by the time cards came out that directly support 720k and 1.44 meg drives, I moved onto the 286 level of computers.
Click to expand...

I used 5.25" 720K drives, which were available long before the 5150. Just shows you how "state of the art" the 5150 really was.
 
Chuck(G) said:
It works just fine--my first 5150 had a 720K 5.25" drive as the first drive (I moved the 360K to the B: slot).

Look, the track format's the same (8/9 x 512); the rotational rate's the same (300 RPM)--the BIOS doesn't put limits on cylinder number (40 vs. 80). Essentially, a 720K drive appears as a 360K drive with double the number of cylinders. After that, it all depends on what version of DOS you're using.

What I don't recall is if PC-DOS 1.1 actually had a FAT ID byte for 720K--I'll have to check.

<curmudgeon>
It'd actually be more interesting if some of the people who were after an authentic 5150 experience actually ran DOS 1.1 instead of a later version.
</curmudgeon>
Click to expand...


I have tried DOS 1 all the way up to IBM Dos 7, they all worked more or less.. :>
 
Anonymous Coward said:
Is it possible to install the last release of the XT BIOS on a 5150? If so, that might help with the 720k support.
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No. The XT uses other switches for number-of-floppy-disk-drives and the switches are examined on the high-nibble of port 0x61h instead of the byte at port 0x60h. Vital parts of the BIOS relay on those switches (like what video card installed, etc..).

The only way to overcome the problem is to make a ROM-Card (it's pretty easy to make one, all you need is an (E)EPROM burner, an (E)EPROM and an adress decoder. The (E)PROM should be) containing the later revision XT BIOS call 13h after a standard BIOS Extension Header.
 
Chuck(G) said:
I used 5.25" 720K drives, which were available long before the 5150. Just shows you how "state of the art" the 5150 really was.
Click to expand...

I was very young, so I only had access to what was given to me.. in them days almost everyone I knew had a c-64, I had an IBM XT .... cause I was special, one guy had an apple ii.

:eek:
 
frozenfire75i said:
Why can't ya boys just leave the 5150 alone the way it was ment to be, If you want VGA 760KB floppys Model M's then go find an collect a PS/2.
Click to expand...

I think the idea is, is to push the 5150 as far as it can go and see how far it can go which is what its creators intentions were in the beggining no?

Personally I think if you have a 5150 in fabulous shape leave it alone, if you have one that has been around the bend, and in less than fabulous shape, then go ahaed and play with it, just leave the nice looking ones alone :mrgreen:
 
I have no particular problem with 3.5" disks in a 5150, although I feel that they look best with the dual full-height drives. If it bothers you that much, you could always use an external 3.5" drive like the 4865.

Here's the details on 3.5" drives in XTs. When you boot DOS up, it checks what type of floppies you have. If the BIOS reports a 3.5" drive, it will set itself up accordingly. 5150s and early XTs (also ATs with the first revision BIOS) don't know about them, and will report back a 5.25" drive. You then use DRVPARM or DRIVER.SYS to set the drive type correctly.

You shouldn't have any problem with 3.5" booters, since they perform the proper INT 13h calls to access tracks beyond 40.
 
Anonymous Coward said:
Is it possible to install the last release of the XT BIOS on a 5150? If so, that might help with the 720k support.
Click to expand...
The aftermarket Award XT BIOS includes support for high-density floppy drives, up to 1.44 MB (assuming your controller is capable of such). My CompuAdd 810, a 9.54 MHz NEC V20 "turbo XT" clone from 1990, uses the Award XT BIOS and has a built-in high-density floppy controller.
 
I've done a bit of research on this in the past.

The answer depends on the version of DOS that the boot diskette is using. All versions of DOS encode a diskette format type in the boot sector. The later versions of DOS will read that format type byte from the boot sector at boot time and use that.

For example, a stock IBM PC 5150 with 5.25" drives can have the boot drive swapped with a 720KB drive and boot from it, if the 720KB diskette was formatted normally. At boot time all machines read the boot sector, and the later versions of DOS go by what they find in the boot sector of the diskette.

DRVPARM and DRIVER.SYS are needed to convince DOS that a diskette drive is something else when that boot sector is not available, or not encoded the way you want it to be.
 
frozenfire75i said:
Why can't ya boys just leave the 5150 alone the way it was ment to be, If you want VGA 760KB floppys Model M's then go find an collect a PS/2.

I don't understand why take something that is historical and mod the shit out of if, upgrade it like it still was in use in the late 1980s?
Sorry if it piss's anyone off, I just don't understand!
Click to expand...

It's not really your business on how people choose to use their personal machines. If you don't like it, don't look.

Using a different keyboard might make the machine more usable for somebody who doesn't like the layout of the original keyboard. I'd hardly call that 'moding the shit out of it'. VGA cards let you minimize usage on vintage monitors. And 720KB drives (there is no such thing as 760KB) have been around since 1983, and specific drives might be older than specific 5150s, which were sold until 1987!
 
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