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PCI Bus Mastering in DOS

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First post, by AvalonH

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Does PCI bus mastering matter in Dos or offer any speed improvement (SVGA games). Using a SE440BX-2 motherboard that has PCI bus master slots I tested a few cards.

1999 Vodoo 3 3000 PCI - no bus mastering
1996 DIamond Steath 64 VIDEO VRAM PCI - no bus mastering
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1994 Mach 64 PCI - supports bus mastering
1993 Mach 32 PCI - supports bus mastering

Also tested some promise PCI ide controllers just to check and they all enable bus mastering.

This was in DOS 7.1 using various utilities like NSSI that show PCI slot information. Surprised me the older cards enable it in dos but not the newer cards.

Reply 1 of 2, by Grzyb

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AvalonH wrote on 2020-03-24, 19:08:

1994 Mach 64 PCI - supports bus mastering
1993 Mach 32 PCI - supports bus mastering

Interesting...
Bus mastering is useful when the card pushes data to the host's memory, eg. in disk controllers, network adapters, frame grabbers...
But why would bus mastering be used by a regular graphics card?

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Reply 2 of 2, by Tiido

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Card can most probably move data faster than CPU can in its tightest loop when doing GUI acceleration operation such as scrolling which is where bus mastering probably comes in on those video cards.
In DOS there's gonna be no interface for such a thing to be used and nothing will even know such a stunt could be possible.

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