Atari and Commodore versions on SAME side of a floppy

[ggn]

4 hours ago, Rybags said:

Generally Amiga bootable games didn't use a filing system, as per Atari 8-bit and many ST games.

 

That cover disk I suspect would be files only... and generally ST cover disks only used an AUTO folder.

 

But even AUTO folder implies the use of FAT, so you'd need a few more sectors in the first track to contain the necessary info. Not that it's impossible, just probably a bigger hassle than just writing some code on the bootsector that loads the data using more primitive calls.

 

4 hours ago, Rybags said:

 

The thing I'm interested in though is whether you could have coexistent boot sectors for both ST and Amiga.  I suspect the answer is yes.  And I suspect that such a track could probably be created on the Amiga (and ST uses 512 byte boot sector - though that said, DBasic for the ST used a 1K sector custom disk format, with 512 byte boot sector - though I've never seen a disk image of it suitable for emulation)

There exists a dump of DBasic and it is in my TODO list to make a custom format routine, write the sectors from that dump and then image the disk using Pasti or similar (first of course I'll verify that the thing works!)

 

1 hour ago, ivop said:

Interesting. As they both run a 68k, I suppose it should be possible to detect if one is running on an ST or Amiga. Do Amiga disks use the same FAT12 boot sector? Otherwise, it could become tricky.

I assure you that the boot sectors on ST and Amiga are really different. Amiga's boot block (as I've read it being called) is 1k, so it uses 2 512b sectors. The ST's is sort-of-kind-of FAT compatible, so ST disks can be read on DOS machines.

 

From the description of the Amiga disk format I can speculate that the special disk has an area that has the markers for a few Amiga sectors, and the rest formatted in a way that the ST can find the FAT sector markers. The above disk picture says that it's made by Rob Nothern, who had access to a TRACE machine, so it wouldn't be too difficult for him to program a custom format that has the scheme I described here.

[Rybags]

The sector format isn't compatible to begin with (though I believe WB >2.0 should be able to read ST disks by default), and additionally the data structure for the boot sector would just about certainly be different enough to make it not feasible.

 

ST can also read/write a track at a time but since some values > $F8 range are used to issue controller commands it's (write) only really useful for doing initial formatting.

 

ed - didn't see that post from ggn when I was typing.  Nice to know though that someone is putting efforts into DBasic.  I did my 1050 emulator using the assembler within it, though all my floppies went when I sold a 1040 about 15 years ago.

Edited May 9, 2021 by Rybags

[ijor]

On 5/7/2021 at 10:55 PM, carlsson said:

Assuming there were custom machines used for disk duplication rather than regular floppy drives connected to some computer, wouldn't those duplicate both sides at once so fitting everything on one disk side or on two sides might not make much of a difference?

 

I don't think there were such drives at that time.

 

14 hours ago, Rybags said:

The thing I'm interested in though is whether you could have coexistent boot sectors for both ST and Amiga. 

 

Yes, you can have both boot sectors in the same track. That's how most of the dual format commercial games work.

The Amiga and the ST both use the same MFM encoding. But the low level sector format (sync, header, checksum) is different. So each platform would read its own sectors without conflict

 

[+Nezgar]

18 hours ago, Mclaneinc said:

Wow, the joy of AA, always giving info you didn't know...

 

We all knew of flippy's but on the same side, new to me....Never saw one of those in the wild, great idea...

Next we'll find cassettes that load 2 platforms from the same side. Maybe Atari data on the right channel, C64 data on the left channel... !? ?

[Rybags]

C64 uses a mono head which I believe covers both tracks.

I can't think of an incredible number of machines that had inbuilt tape deck or used a proprietary one.

System 80 (TRS-80 clone) sold here and by other names elsewhere has a built in deck.

The early Amstrads.

 

Creativision (though it was primarily a console) I think you supplied your own unit.

Other systems where you supplied your own unit I would think they'd recommend you use the left channel if the choice is available - the left channels are at the outer edge so no chance of one interfering with the other.

[carlsson]

Creativision uses a custom tape recorder that has separate channels if I recall correctly. It is attached to the main unit so it looks like an integrated system. Its BASIC also stores programs as ASCII character by character, not tokenized IIRC.

[Mazzspeed]

All I know is I was wrapped when I worked out Linux can handle the Amiga's FFS (Fast Filing System).

[thorfdbg]

On 5/8/2021 at 3:32 PM, ggn said:

I'm not exactly sure what you mean there, but according to the docs (and from my sparse knowledge of the Amiga) there is a bootblock area on the Amiga that's 1024 bytes long.

The boot sector does not matter unless you attempt to boot from the disk. The boot sector is only read from the bootstrap Os code, but not by the filing system.

 

The file systems of Amiga and Atari are completely different. However, as long as the sectors and tracks of the first file system are marked "occupied" for the second file system, it does not matter. I do not assume that the file systems are identical (they are not).

 

On which side of the disk the "other filesystem " tracks are does not matter. The Amiga uses both sides, interleaved. Hence, it does not help to isolate the alien file system on one side of the disk.

[thorfdbg]

23 hours ago, carlsson said:

I wonder if the fact that the Amiga reads (and writes) an entire track at a time is the reason why Chinon drives in Amiga 500 usually are completely worn out and doubtful if those can be refurbished, while equally old Chinon drives in Atari ST often are perfectly fine.

I doubt it. The mechanical wear is identical no matter whether the whole track or only a single sector is read. I would guess it rather depends on how often the drive head seeks, and how long the disk rotates.

[+Eyvind Bernhardsen]

15 hours ago, thorfdbg said:

On which side of the disk the "other filesystem " tracks are does not matter. The Amiga uses both sides, interleaved. Hence, it does not help to isolate the alien file system on one side of the disk.

A lot of the early STs had single-sided disk drives, so it would make sense to put all the ST files on that side. Amigas always had DS drives.

[ggn]

On 5/9/2021 at 3:18 AM, Rybags said:

ed - didn't see that post from ggn when I was typing.  Nice to know though that someone is putting efforts into DBasic.  I did my 1050 emulator using the assembler within it, though all my floppies went when I sold a 1040 about 15 years ago.

@Rybags (and anyone else interested): Dbasic has been archived from an original disk here!

[sanny]

On 5/9/2021 at 5:33 PM, thorfdbg said:

I doubt it. The mechanical wear is identical no matter whether the whole track or only a single sector is read. I would guess it rather depends on how often the drive head seeks, and how long the disk rotates.

 

I think the Amiga, if no floppy is in the drive, permanently checks every few seconds of a floppy was inserted. Gives an annoying sound every few seconds.

Whereas the ST leaves the drive alone unless it's accessed on purpose.