@Lemmink:
The reasons for slowdown with the A2091 and no ZorroII fastmem comes from the fact that the only thing ZorroII cards can DMA to/from in a ZorroIII system is chipmem and ZorroII fastmem. So the slowdown in that case comes from the fact that the A2091 is doing DMA to/from buffers in chipmem.
The reason why I am so anti ZorroII in a ZorroIII system is that the ZorroII cards use many times more "possible" bandwidth on the Zorro-bus than ZorroIII-cards. As I mentioned in an earlier post, the percentage of maximum ZorroII bandwidth a ZorroII-card uses is equal to the percentage of ZorroIII bandwidth that lost.
Only using a ZorroII ram-expansion would as you say not be used until all other faster memory is used, so a ram-expansion only would be ok I guess even if it is rather pointless.
Though using a ZorroII scsi-controller is very uneffective and there are a number of scenarios of uneffectiveness
:
1. You have no ZorroII fastmem and a controller using DMA:
Data will be shuffled to buffers in chipmem over the Zorro-bus using DMA and then the cpu will be working on the buffers in chipmem.
2. You have no ZorroII fastmem and a controller not using DMA:
Data will be shuffled over the Zorro bus by the cpu to 32-bit memory and then the cpu will be working on the buffers in 32-bit memory.
3. You have ZorroII fastmem and a controller using DMA:
Data will be shuffled to buffers in ZorroII fastmem over the Zorro-bus using DMA and then the cpu will be working on the buffers in ZorroII fastmem.
4. You have ZorroII fastmem and a controller not using DMA:
Data will be shuffled over the Zorro bus by the cpu to 32-bit memory and then the cpu will be working on the buffers in 32-bit memory.
5. You have a special controller like the Impact series II:
Data will be shuffled to buffers in the memory of the Impact Series II card without touching the Zorro bus by the DMA and then the CPU will be working on the buffers in the ZorroII-memory of the Impact Series II.
Scenario 1 is extremely bad because of the chipmem and scenario 3 is extremely bad because of the double data transfers on the Zorro bus. Scenario 2 and 4 are also very bad because they need the cpu to do all the work, but it only hogs the bus half as much as scenario 3. Scenario 5 is the most sensible of them, but they are all bad from a performance perspective and a bus hoging perspective.
One more reason a ZorroII card is bad in a ZorroIII system is because the thing that makes DMA stand out is lost as ZorroII cards cant move data directly to the fastest memory closest to the cpu.
blablabla..
.
/Patrik
