Hard disk driver situation confusion

[Smonson]

I'm very confused by the ACSI hard disk situation. I can see that there are many drivers available, with various featuresets. Could someone answer a very basic question for me?

How come a hard disk driver isn't needed when using an emulated hard drive in Steem or Hatari? Does TOS already have the built-in capability of accessing a hard drive? The desktop doesn't appear to have any way to add hard disks; they just show up as icons at boot, in those emulators, suggesting that it must scan for them on startup by interrogating the ACSI port to see what's on it, if anything. Is that correct?

[exxos]

I assume emulators have a built in feature to emulate the drives. I mean they can use extended video resolutions and do all sorts "out of the box".

I don't think it would make any sense to have a driver like HD10, there isn't a physical port to connect to ,and no use in emulating one.

[Smonson]

So how does TOS access the emulated drive? Does it see it as an ACSI device that behaves in a very standards-compliant way and therefore doesn't need an additional driver?

[exxos]

They will just have their own built in driver which TOS will see as normal gemdos drives.

[czietz]

How come a hard disk driver isn't needed when using an emulated hard drive in Steem or Hatari?

That's not exactly true. If you use an emulated ACSI, SCSI or IDE drive in Hatari, you need a hard disk driver (or EmuTOS) like on real hardware. Same with the ACSI image option in Steem SSE. Only if you use the GEMDOS HD emulation (or the corresponding feature in Steem), you don't need a driver. In that case, the emulator intercepts the OS calls to open files, list directories, etc., and handles them by providing data from the host's file system.

[rubber_jonnie]

I pretty much only use GEMDOS in emulated machines, but I have used images attached to them and a driver is required for ACSI.

The drivers I've used over the years are:

AHDI
CBDH
ICD Pro
PPeras HD driver
HDDRIVER

To be fair I've only used HDDRIVER recently, and only in demo form. But the last two are the newest as they are current. I use PPeras driver for ACSI with my CosmosEx.

It's a great driver with nice utilities.

HDDRIVER is probably the best overall, but costs €45 compared to €10 for PPeras driver.

[Smonson]

If you use an emulated ACSI, SCSI or IDE drive in Hatari, you need a hard disk driver (or EmuTOS) like on real hardware. Same with the ACSI image option in Steem SSE. Only if you use the GEMDOS HD emulation (or the corresponding feature in Steem), you don't need a driver. In that case, the emulator intercepts the OS calls to open files, list directories, etc., and handles them by providing data from the host's file system.

I think this is the answer I was looking for - thanks czietz. That explains why a standard TOS image (I use UK 1.04) can see a virtual hard drive in emulators while a real machine apparently cannot.