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160KB vs 180KB set me straight on these please

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voidstar78

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So, when I entered the PC world, I was spoiled and had DD 360KB drives available.

I never had to flip disks. But I've seen it done. Except not sure if that was on a IBM (maybe it was on a TRS-80 system).

When PC-DOS 1.0 came out - it was on a 160KB formatted single sided disk, correct? Was disk flipping ever a thing on the IBM PC? Cause I read there was a 320KB format - so 160KB is a single sided, and 320KB was double-sided? [ you could load BASICA, flip the disk, and save BASIC programs on the other side of the boot disk? ]


But then there was 180KB and 360KB. Was this using the same drives in the original (model A) 5150, but needed a BIOS update to support? [ and in the early days, it wasn't a big deal to order or obtain a BIOS update chip from a computer store or IBM mail-order themselves? ]


Like I was looking at Microsoft Adventure, and its little document says it is a "non-dos" 180KB disk (of which WinImage won't read).


The HxC device I got - that emulates disks - it'll support those 180KB images, but not the 160KB images. So the earliest PC-DOS I was able to boot (in the 5150 model B) was PC-DOS 2.10 (which I understand now they added 360KB {or 180KB single-sided} support in v2, so that makes sense).


Now I've read that there is some hex codes that have to get added to the 160KB images - is that to make them work with newer BIOS or newer disk controllers? (or both?) So at some point, when you upgraded the BIOS of a 5150 model A -- it would no longer read those earlier 160KB formatted disks?


Just kind of confused, since I'm having trouble running Serenia and Adventure on my 5150 (model B).
 
On the PC, flipping the disk was never possible due to the index hole. This only works on systems that don't rely on the index hole like the C64, Atari 400/800 for example.

The original 160 KB single-sided disks were a DOS 1.x thing. With DOS 2.0, they changed the disk layout slightly to allow 180 KB single- and 360 KB double-sided. At least that's what I remember.
 
Timo W. said:
On the PC, flipping the disk was never possible due to the index hole. This only works on systems that don't rely on the index hole like the C64, Atari 400/800 for example.
Click to expand...
AFAIK the PC drives don't use the index hole as well. And if it does, I don't see any reason why things wouldn't work when flipping the disk. I think you mean the write protect hole. And the C64 relies on that as well. To use the other side of a disk we simply cut a hole in the other side of the disk. You could even buy a little tool to do that for you.
 
Drives came in either single sided or double sided. IBM chose originally to only use the single sided drive because the early double sided drives sometimes mangled disks. Single sided disks gave a format of 160K in DOS 1 and 180K in DOS 2. In 1982, double sided drives were offered by IBM and DOS 1.1 supported them. Double sided drives gave formats of 320K for DOS 1.1 and 360K for DOS 2.

Flippy disks were used on some IBM PCs with only single sided drives. It was easy to punch a second index hole in the nylon covering. Not common, the double sided drive came into service so quickly. Even weirder, there was a utility that let DOS 1.0 systems use both surfaces of a double sided drive as two single sided disks. The lower surface would be Drive A: and the previously unused upper surface was treated as Drive C:. The second drive would be used as B: and D:.

Going for 180K or 360K required upgrading to at least DOS 2.0. The original PC BIOS would work with DOS 2.

DOS 2 made another change to the disk format. It added the BIOS Parameter Block that describes the disk in detail. DOS 1 formatted disks lack the BPB and newer code that relies on the BPB won't work. DOS 2 should read DOS 1 formatted disks so the 160K should still be readable with all 3 PC BIOS revisions. Something else is happening but I didn't play many DOS 1.x games so someone else will have to know.

Note that the gaps between sectors is different from DOS 1 and DOS 2 with the 160/320K formats. DOS 1 spreads the 8 sectors per track out across the disk. DOS 2 does the 9 sector per track format and then effectively ignores the last sector. It is possible that copy protection schemes won't like the difference.
 
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Well, I got Serenia to extract into 3 files: SERENIA.COM, GAME.DAT, SAVE.DAT. The two DAT files are 160KB - Maybe when Ken/Roberta made it, they only had the single-sided 5.25" drive available (one for their compiler/assembler or whatever tools, the 2nd drive to hold the created content -- I'm not sure if Serenia has any "insert disk 2" prompt {and wouldn't/shouldn't once 360KB disks could be used}).. But the SERENIA.COM is only 485 bytes, so I assume it loads "more of itself" from one of the DAT files. I'm not sure if the game was ever released on 160KB disks (if so, then it would have been 2x disks? not a single flippable disk - right?), or if it was released on 360KB (but just curious to me that its two main files are 160KB).
NOTE: Serenia might not be running for me for different reasons - like I'm trying to run it from a HDD. Maybe it doesn't like being in a sub-folder or something. Or maybe since I don't have the older CGA card installed, it's spazzing out. I'll try putting back in the CGA, and running it from a root A: folder, and see if that gets it going (while also booting to PC-DOS 2.10).


As for Adventure, I can't even get WinImage to open the 180KB IMG file (pardon I thought it was 160, but it's actually 180). So I haven't yet extracted any files to even try to run. But I think I can toss it into my HxC emulator and boot from it - so I can probably get that to run.


That leaves PC-DOS... My HxC device won't accept the 160KB image. I tried hex-editing it once with some online recommended stuff, but I think I fouled that up (lousy hex editor), and gave up since PC-DOS 2.10 was old enough for my interests.



But thanks for the clarification - the very earliest 1981 5150 model A's did come with single sided drives? I guess I always assumed all the 5150s were always double sided.


I'd heard the "horror stories" of those early day disk drives messing up - like the disk drive manuals for the early Commodore PETs has some clear warnings on things to do and not to do with their disk drives, like this stern "sequence of operation" to properly get a disk inserted, head aligned, spooled up, and a proper shutdown/removal procedure. [ funny, that's like the early days of USB - you really didn't want to just yank those out, but eventually they seemed a bit more forgiving ].
 
You may be running into copy protection at this point which is causing your old games not to run.
Disk image files may or may not be able to reproduce any copy protection that was on the original disk. Once files are extracted from an image, any copy protection will definitely fail (that's the whole point).

There are many, many games that have already been liberated from the confines of their original media and on-disk protections ready to be run directly off your hard drive or in an emulator which can save you a lot of time trying to do this type of work again. I can direct you to such an archive if you're interested.
 
Timo W. said:
No, I mean the index hole. The PC uses it and there is only one on one side. If you flip the disk, the sensor is always blocked and the PC will not find the index mark.
Click to expand...

Yes, this. Most computers that used standard (or close to it) Shugart interface drives with MFM controllers cared about. Oddball GCR things like Commodore and Apple often didn't.

There were a few manufacturers that sold pre-punched "flippy" disks with the second write protect notch and index hole already present. These weren't super useful for PCs by the time they came out but there were still plenty of single-sided TRS-80s, etc, floating around in the early 80's. (And of course you could use them on Commodores, etc.) These things were subject to an endless debate about whether flipping your disks would eventually destroy your floppy drive.

(The theory was that since the direction of rotation changes when you flip the disk over it might cause the dust that was supposed to stay stuck to the fluffy lining of the disk sleeve to come loose and pile up on your drive head more readily. I don't know how much water that theory actually holds.)
 
voidstar78 said:
That leaves PC-DOS... My HxC device won't accept the 160KB image. I tried hex-editing it once with some online recommended stuff, but I think I fouled that up (lousy hex editor), and gave up since PC-DOS 2.10 was old enough for my interests.
Click to expand...

I assume you're trying to use a "raw" disk image of DOS 1.x; have you tried converting either that or a more "intelligent" source format like Teledisk into a native HFE file using the HFE disk image tools? The HxC firmware might be mis-guessing about the format when presented with the raw version but should be able to figure it out if it's saved as an HFE, which explicitly specifies all the format details.

For laughs I downloaded PS-DOS 1.00 from the usual suspect (WinWorld) and tried it out using my Gotek emulator running FlashFloppy. Score one for open source I guess because FlashFloppy is able to read both the Raw version and an HFE converted from the Teledisk image.

(Possibly useful tip: Apparently if you have a driveparm command in your config.sys, which I had to tell all the DOS-es installed on my hard disk to use a 720k format for drive A: instead of 360K, it breaks being able to read 8 sector disks. Got a general failure reading drive A: trying to do a DIR despite being able to boot from the disk before I made a wild guess and REM'ed it out.)
 
You can get around the 160KB issue by simply using a later version of DOS to format a 180K (or 360K) floppy and DISKCOPY the 160KB image over. DOS 2.X actually formatted 180K (9 sectors) when asked to format a 160K disk. Only the first 8 on the track were used.
 
PC DOS 1.0 only supported single-sided 160 KB disks.

PC DOS 1.1 and MS-DOS 1.25 added support for double-sided 320 KB disks.

PC/MS-DOS 2.0 increased the number of sectors per track from 8 to 9, increasing capacity to 180 KB single-sided and 360 KB double-sided.
 
Ah, maybe the copy-protection part is what they meant by "non-dos" (with the intentional bad sectors at certain offsets?), and maybe it's why WinImage is having trouble with the images.

I never knew the manual to Serenia was so elaborate. Interesting how both Adventure and Serenia got some serious attention from IBM (in terms of somewhat formal looking manuals, with tutorial on using the overall machine). I vaguely remember those serious looking grey IBM "books" on the shelves of computer stores. But in this case, within all that formality, you have page 16: an encoded hint on what to do with the snake, and a comment "if...totally stuck and about to burn... the disk," (and gives several suggestions). Classic Sierra, but kudos to their IBM connection and making such a nice manual for a 48K game.


Then I found an old article in an '86 PC Mag - it's more of an advertisement for the Kraft joystick, but around it has this "list of copy protected games" and most of these old titles are on that.


Yeah I just wanted to try a few of these on an original 5150. And I was going to prepare some setup guides for the 5150, but I wanted to understand how much I'm taking for granted using an '84 model B version that already has newer BIOS (which I do have functional pair of 360KB DD drives - which should be able to boot a PC-DOS 1.0 if I could come across the disk media someday?)
 
voidstar78 said:
Yeah I just wanted to try a few of these on an original 5150. And I was going to prepare some setup guides for the 5150, but I wanted to understand how much I'm taking for granted using an '84 model B version that already has newer BIOS (which I do have functional pair of 360KB DD drives - which should be able to boot a PC-DOS 1.0 if I could come across the disk media someday?)
Click to expand...

Have you tried an .HFE image? Let me see if the forum will let me attach one. I would be deeply, deeply surprised if the HxC won't support an 8-sector disk if it's explicitly specified.
 

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The 1.0 HFE worked fine with my HxC, thanks! Though remember PC-DOS 1.0 I think supports only 160KB formats (read or write), need PC-DOS 1.1 to get 180KB support. [ EDIT: actually PC-DOS 2.x for the 180KB ]

I'm still not quite understanding these "non-dos" disks. Like Microsoft Flight Simulator 1.0 - how is it booting?
 
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voidstar78 said:
The 1.0 HFE worked fine with my HxC, thanks! Though remember PC-DOS 1.0 I think supports only 160KB formats (read or write), need PC-DOS 1.1 to get 180KB support.

I'm still not quite understanding these "non-dos" disks. Like Microsoft Flight Simulator 1.0 - how is it booting?
Click to expand...

PC-DOS 1.1 supports 160K and 320K. PC-DOS 2.0 is the first version to support 180K.

Non-DOS booter include what amounts to a very limited operating system. I remember there was a web page describing some of the booters but I can't find it now.
 
the 8-bit guy has a video about boot sector games.
https://www.youtube.com/watch?v=1UzTf0Qo37A

The same mechanism (the BIOS) that allows a disk to be able to boot an operating system from a disk also allows a game to directly read and write sectors on a disk, allowing the game data to be loaded and then jumped to for execution. Save games and high scores are often saved in dedicated sectors. Developers did boot sector games for three reasons:
1) maximize the amount of memory available to the game. No DOS means more memory available.
2) maximize the amount of storage space available on the floppy for the game.
3) copy protection.
 
One of these drives is 160KB one is 360KB, Can you spot the difference?double.jpg

single.jpg

one has two head connectors one has only one head connector...
 
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