Which is the better scsi card for the A4000?

[alexh]

They are both pretty crap.

Both are Zorro II without DMA and so offer no bandwidth or CPU load advantages over using the A4000's IDE.

Unless you've got a SCSI device you want to use... I'd leave them "lying around" and save electricity.

[alexh]

isn't SCSI still faster throughput than the early IDE channels found on classic Amigas? even without the DMA?

I don't think so. Both are PIO and both are 16-bit.

[alexh]

A GVP card with some RAM on it should work use the CPU far less than IDE. But if you have a fast CPU then it will be slower.

[alexh]

I am still a little confused at how and when the Amiga made use of PIO versus DMA, specifically with SCSI and IDE configurations.

The hardware must be DMA bus master (whereby the SCSI card initiates DMA transfers). The IVS Trumpcard Pro, Dataflyer Plus and Gayle IDE all do not support DMA of any kind.

I remember it was always a big deal that the Amiga had DMA channels

The Amigas DMA channels are between the custom chips and Chip-RAM. Gayle IDE does not have a DMA channel.

[alexh]

Well, only to ZII memory.

Yes I think this is true. A GVP controller with RAM for example has DMA. You must use the memory mask fields in the RDB to constrict the memory the SCSI driver will use.

Obviously this RAM is 16-bit and has a bandwidth limitation when used by a 32-bit CPU.

Some accelerators have their own 32-bit CPU, 32-bit RAM, SCSI controller and DMA controller to overcome these problems. (Cyberstorm for example.)

[alexh]

Is Gayle the IDE controller in AGA machines?

And in the A600, on the Viper A530 Turbo card, and re-created in the IDE68k addon.