Configuring Promise VLB IDE in Win9X \ VOGONS

Configuring Promise VLB IDE in Win9X

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First post, by nztdm

Posted on 2024-11-01, 10:48

nztdm Offline

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Joined: 2018-02-16, 22:12

I have a 486 system with a Promise PDC20630 IDE interface.

If I use the DOS driver in CONFIG.SYS, setting the HDD to MWDMA2, I get >13MB/s sequential read in DOS (Speedsys).

In Windows 98, using Standard IDE driver or the Promise Win95 driver, I can only get the base 2-3MB/s.

The Win95 driver has no settings for which PIO mode or DMA mode to use.
The DOS driver and the 32-bit Win3.1 driver both have these settings.

Running the DOS driver before Win98 loads makes it slower.
Various versions of Promise BIOS Extension set lower modes that only work in DOS.
None of the card jumpers set a MWDMA mode.

Any idea how to set the Promise PDC20630 to MWDMA2 in Windows?

Reply 1 of 2, by swaaye

Posted on 2024-11-01, 15:06

swaaye Offline

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I opened the Win95 driver (PTIVGAPI.MPD) in a hex editor and it looks like there is a list of drives. I think it's set up to recognize specific drives and has a table of parameters for those drives. If I remember right, the DOS driver does this too but you can also manually configure it or have it test the drive (which wasn't always reliable). I don't see a way to manually configure the Win95 driver. Maybe you could hex edit it and replace one of the drives with your drive if you can decipher what's going on in the driver.

Also, these cards only do DMA from card to drive. The system is still communicating with the card with a PIO mode. This means it's still going to have a high CPU load.

Reply 2 of 2, by nztdm

Posted on 2024-11-02, 06:50

nztdm Offline

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Rank: Newbie
Posts: 75
Joined: 2018-02-16, 22:12

swaaye wrote on 2024-11-01, 15:06:

I opened the Win95 driver (PTIVGAPI.MPD) in a hex editor and it looks like there is a list of drives. I think it's set up to recognize specific drives and has a table of parameters for those drives. If I remember right, the DOS driver does this too but you can also manually configure it or have it test the drive (which wasn't always reliable). I don't see a way to manually configure the Win95 driver. Maybe you could hex edit it and replace one of the drives with your drive if you can decipher what's going on in the driver.

Interesting. Good find. I can see the manufacturers and model numbers you mention. I wouldn't know where to start to modify it.

swaaye wrote on 2024-11-01, 15:06:

Also, these cards only do DMA from card to drive. The system is still communicating with the card with a PIO mode. This means it's still going to have a high CPU load.

Yes I understand that. The benchmarks are improved nonetheless.

I have a DTC 2278E which is my second fastest VLB IDE. It supports up to PIO Mode 4, and gets ~7MB/s with the Win98 driver. But it doesn't like the faster bus speeds that the Promise card works with.
This will be the best choice for Win98 if I go to a lower bus speed, as the Promise Win95 driver gets only half that speed.
The PDC20630 seems to remain king for DOS and Win3.1.

An odd test:
Installing the Win3.1 driver in Win98 (via System.ini), works...ish. This driver supports specifying speeds.
Windows complains with a 32-bit disk access warning bluescreen during boot, but continues.
Setting to max speed PIO gets 7MB/s.
Setting to IORDY PIO gets 9.3MB/s.
Setting to any speed DMA crashes at boot.
Setting to auto detect results in 9.3MB/s.

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