Sure, with Win95 you might see some differences. It will depend on how bad your specific VLB IDE solution is. First off, bench the current setup in Speedsys or something.

I think bus mastering is more of a PCI thing.
Have you tried Speedsys to test hard drive performance with your current controller in plain DOS? Are you using any DOS or Win95 drivers for it?

First results with 407MB seagate as PM
No special drivers. No smartdrv

Second results with 160GB seagate PIO4 as PS.
No special drivers. No Smartdrv

Double checked with Norton SI. Highest transfer rate = 1.6mb/s. Not too much and not really sounding like VLB

Screenshots updated

First of all, I think there might be terminology confusion. Some early SCSI vendors, used "bus master controller" term irrespectively if it actually used any bus-master DMA technology on the ISA/VLB side of interface or not. So your ISA card might not be actually using any controller arbitrated bus transfers meant to free up CPU.

Secondly, even if it does. Unless you have a very special needs (such as running a server), in the Windows 95 era it is better to go for throughput (read the PIO VL-Bus controller) rather than low CPU utilisation.

In order to benefit from reduced CPU utilisation during I/O you need to be able to use those extra CPU cycles for something useful. Which wasn't always the case in those days of "baby" multitasking. In the mid-'90s. In those days you first loaded the program to RAM and then ran it as opposed to loading and doing something CPU intensive at the same time. Sw tasks weren't simply that demanding back then (and hardware was weak).

PCI bus-master DMA as introduced in first Triton chipset was a different kind of animal.

Your BIOS doesn't have any IDE-related options?
I found a picture of the CH-471B and it looks like it has an Appian ADI/2 for VLB IDE. Looks like someone has a DOS .SYS file for it on here: http://www.os2site.com/sw/MARTIN/drivers/storage/index.html Should work for speedsys but may or may not cause Win9x to go into compatibility mode though.

My guess is that those PIO/UDMA modes displayed are what the the drives support at maximum, not what they are actually running at .

By the way, those screen photos are extremely hard to read .

Unfortunately I’m not using OS/2.
I have no options in the bios to set for hdds. Anyway the limit of 1,6mb really looks like there might be wrong active PIO mode. I’ll dive into it

Ps. Thanks also for the perspective on SCSI/bandwidth in general

Marco wrote on 2020-08-19, 21:12:

Unfortunately I’m not using OS/2.
I have no options in the bios to set for hdds. Anyway the limit of 1,6mb really looks like there might be wrong active PIO mode. I’ll dive into it

Ps. Thanks also for the perspective on SCSI/bandwidth in general

I think you might have misunderstood, the appian_adi2_1995-02-10.zip includes DOS drivers too .

Ahhhh thanks a lot.

Might it be useful to play with the vesa settings of the bios like
- DMA clock Speed 4/8MHz (as is 4)
- Latch time 2-3WS (as is 3)
- ... synchronize time: 4nS/... don’t remember correctly.

Anyway I check the driver thanks for this finding!!!

So indeed the Norton SI jumped up to 4,3Mb now after installing the driver.

Speedsys although now hangs while initializing atapi
I assume that the system is using the lowest common PIO per channel before meaning my second hdd would run on PIO3 also only. An assumption.

Again thanks a lot for the hint.

Seeing these revised numbers now what you say regarding SCSI adapter?

Sadly the driver also seems incompatible with mscdex. Total system hang while loading. Ahhhh

I wouldn't recommend SCSI for anything unless your after period builds.
It's expensive (compared to IDE) noisy and HDD's will have had many more hours as many are from servers.
Your much better off going something like CF or SD adapters on machines without PCI IMHO.

Also that old ST3491A isnt the fastest disk in the first place.
https://stason.org/TULARC/pc/hard-drives-hdd/ … -ATA2-FAST.html

Can't help with the driver though, sorry!

Alright thanks. I just don’t want to go for CF or similar since I’d like to build authentic system from these days - possibly with best components available at that time.
Yeah my ST is quite far away from that 😀))

Ah, well if your after authenticity then SCSI does make some sense.
Hope you do get VLB working though, much more interesting in my books 😀

Yes indeed. Question is only whether SCSI at ISA makes sense since VLB SCSI controllers are much too expensive here at eBay

Ps. I validated: the hdd Controller driver enables multiple PIOs on one channel. That’s why it improves performance on the pio4 drive

I don't see how SCSI would be any faster. The whole reason why IDE used Programmed I/O in the first place was that ISA DMA was so slow that a 286 doing PIO could outperform it.