yes. I've done it with a PC that has scsi controller, an old school sampler that has a controller in it and a hard drive in the middle (this was special it could handle multiple masters!), but you want to make sure only 1 master is "on" at any time and it will work fine.

something to beware of, some master have software termination, that only terminates when the card is powered, so you need to check termination works when its turned off, it could get tricky. it would be easier if both masters were in the middle of the chain and not the ends, then you could terminate the ends of the cables correctly.

I did this when I was a teenager with one CDROM that could be used by 2 computers simultaneousely.
The problem with HDDs is that each operating system has its own buffers. It easily gets out of sync when you are not able to hide partitions from each other.
But to backup a system. Easy going!
Just care about termination and bus length. Fast SCSI limits you to 3 meters.

And, as far as I know the 1542CF may support disks > 8 GB.

BloodyCactus wrote on 2026-07-15, 18:51:

yes. I've done it with a PC that has scsi controller, an old school sampler that has a controller in it and a hard drive in the middle (this was special it could handle multiple masters!), but you want to make sure only 1 master is "on" at any time and it will work fine.

something to beware of, some master have software termination, that only terminates when the card is powered, so you need to check termination works when its turned off, it could get tricky. it would be easier if both masters were in the middle of the chain and not the ends, then you could terminate the ends of the cables correctly.

Yeah, that's indeed a potential gotcha. I have to check Adaptec's documentation (and it's quite an extensive documentation at it), but I'm under the impression it does hardware termination.

Disruptor wrote on 2026-07-15, 20:05:

I did this when I was a teenager with one CDROM that could be used by 2 computers simultaneousely.
The problem with HDDs is that each operating system has its own buffers. It easily gets out of sync when you are not able to hide partitions from each other.
But to backup a system. Easy going!

At the same time? Hell... Everything I've read suggests this breaks hell lose and that my drives will explode in epic flames. Nevertheless, that was a sick setup. When the bus got scanned, did it show the two controllers in the list?

Just care about termination and bus length. Fast SCSI limits you to 3 meters.

And, as far as I know the 1542CF may support disks > 8 GB.

No problem... I'm not planning in running long cables, it just needs to reach another machine in the same room.

As for the 1542CF, it does support large disks depending on the BIOS version (mine, particularly is a B402, seemingly dated from 1995.) From the BIOS, it shows at most 8 GB-ish, but some operating systems do detect the drive correctly, like RedHat, for example.

Thanks for the replies, guys!

Pardon my paltry grammar. I did want to correct the mistakes but it would seem I can't edit posts on Vogons anymore (?)

tadeu wrote on 2026-07-16, 04:13:

Pardon my paltry grammar. I did want to correct the mistakes but it would seem I can't edit posts on Vogons anymore (?)

I believe the edit post function becomes available after a certain amount of posts, don't know the number though (maybe around 20?)

tadeu wrote on 2026-07-16, 04:10:

Disruptor wrote on 2026-07-15, 20:05:

I did this when I was a teenager with one CDROM that could be used by 2 computers simultaneousely.
The problem with HDDs is that each operating system has its own buffers. It easily gets out of sync when you are not able to hide partitions from each other.
But to backup a system. Easy going!

At the same time? Hell... Everything I've read suggests this breaks hell lose and that my drives will explode in epic flames. Nevertheless, that was a sick setup. When the bus got scanned, did it show the two controllers in the list?

Yes of course. One controller was on a differend ID ofc. It was 6.
As they were ROM type drives, there were no problems at all.
Ok, the BUS reset. It may occur when you power one computer on. But that is difficult anyways because you need to ensure proper termination everytime. Bus reset on power cycle or reset can be switched off in SCSI BIOS.
Well, you can exclude some IDs from SCSI BIOS scan, or removable drives like my SyQuest. So it was possible to use 2 computers with one SCSI bus at once.
Due to the caching problem data transfer did not work on-the-fly.

No, as controllers are no targets, they are not shown in the list. Controllers are initiators.
But there were some experiments that put a controller into target mode! However, we failed to reproduce this. It should be possible to get a TCP/IP-link over SCSI on NCR/LSILogic/Symbios 875 controllers.

tadeu wrote on 2026-07-16, 04:10:

Disruptor wrote on 2026-07-15, 20:05:

Just care about termination and bus length. Fast SCSI limits you to 3 meters.

And, as far as I know the 1542CF may support disks > 8 GB.

No problem... I'm not planning in running long cables, it just needs to reach another machine in the same room.

As for the 1542CF, it does support large disks depending on the BIOS version (mine, particularly is a B402, seemingly dated from 1995.) From the BIOS, it shows at most 8 GB-ish, but some operating systems do detect the drive correctly, like RedHat, for example.

Perhaps a BIOS update may help.
My pal mkarcher has written a patch to the VL and EISA controllers from Adaptec; that won't help with your 1542CF.
Showing some love for Adaptec's ugly ducklings: Adding big drive support to EISA and VL controllers
INT13 Extensions to Adaptec 274x EISA & 284x VLB

If you are looking for weird SCSI things:
Extending a SCSI bus with Adaptec AIC-3860Q (2940U2W and more)
SCSI: Over how many brigdes can you walk?

Disruptor wrote on 2026-07-16, 11:20:

Yes of course. One controller was on a differend ID ofc. It was 6. As they were ROM type drives, there were no problems at all. […]
Show full quote

Yes of course. One controller was on a differend ID ofc. It was 6.
As they were ROM type drives, there were no problems at all.
Ok, the BUS reset. It may occur when you power one computer on. But that is difficult anyways because you need to ensure proper termination everytime. Bus reset on power cycle or reset can be switched off in SCSI BIOS.
Well, you can exclude some IDs from SCSI BIOS scan, or removable drives like my SyQuest. So it was possible to use 2 computers with one SCSI bus at once.
Due to the caching problem data transfer did not work on-the-fly.

No, as controllers are no targets, they are not shown in the list. Controllers are initiators.
But there were some experiments that put a controller into target mode! However, we failed to reproduce this. It should be possible to get a TCP/IP-link over SCSI on NCR/LSILogic/Symbios 875 controllers.

[...]

Perhaps a BIOS update may help.
My pal mkarcher has written a patch to the VL and EISA controllers from Adaptec; that won't help with your 1542CF.
Showing some love for Adaptec's ugly ducklings: Adding big drive support to EISA and VL controllers
INT13 Extensions to Adaptec 274x EISA & 284x VLB

If you are looking for weird SCSI things:
Extending a SCSI bus with Adaptec AIC-3860Q (2940U2W and more)
SCSI: Over how many brigdes can you walk?

Thanks for the tips, Disruptor. Always interesting to find a fellow SCSI appreciator, and quite a connoisseur, in your case.

While I don't plan to run two alive controllers in the bus concomitantly, it's at least good to know that this won't automatically trigger fireworks and magic smokes. But I found the SCSI bridge mostly intriguing, as well as the idea of doing TCP/IP over SCSI bus. Quite a wild proposition, but there's indeed something similar for Fibre Channel, I think. Might worth a shot when I have sometime to play with it, albeit I think my very basic late LSI controllers won't play nice with it. I'd probably need an older Adaptec 160 card.

Also, I've checked. The BIOS sees about 4,3 GB. But, like I mentioned, it's not a problem once the proper driver is loaded. This seems to be an issue on DOS or Win9x. OS/2 and NT can see (an maybe use) the entire drive. From what I read, I can place the bootable partitions before the 2 GB mark and I probably can use the rest for files just fine. As for the BIOS itself, even if you guys had one for my card, I don't think I could upgrade it anyway, since it's an parallel EEPROM and I don't have any kind of programmer for it.

In any case, I'll run some tests in the future and maybe create another post to show the janky setup on it's entirety.