Re: direct memory access
From: WinGuy (no_spam_at_nomail.bot)
Date: 07/26/04
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Date: Mon, 26 Jul 2004 01:52:13 GMT
Not just CD and HDD devices use DMA (Dynamic Memory Access). Sound and Video
and some other special purpose devices use DMA technology to directly access
physical system RAM on the motherboard. Sometimes, but primarily only for
older "legacy" devices used on older computers, settings regarding DMA need
to be set in BIOS and not just through the operating system settings. The
operating system itself will not allow a setting if the BIOS reports that
support is lacking. This requirement was pretty much obsoleted by Plug and
Play (PnP) hardware technology, which is why the very newer computers
sometimes don't even have settings available to the user in BIOS regarding
DMA or other assignments of resources such as IRQ. Some old timers might
remember the days when soundcard settings, such as DMA channel and interrupt
(IRQ) and so on, would have to be entered into the autoexec.bat file so that
the card could work with DOS based games based on settings in BIOS for the
device. These things often had to be "allocated" manually in BIOS (and most
people couldn't figure that out, and so PnP was invented).
However, it is unlikely that XP would be being run on such an old computer
and so it is unlikely that manual BIOS settings would be needed. Still, even
some of the newer computers have BIOS provisions for this in order to handle
"legacy" PCI cards that are not fully PnP compatible with todays spec, and
systems special ordered with the much older ISA motherboard slots almost
always have the mentioned BIOS provisions. The PnP spec has gone through
revisions through the years and so, for devices that support the latest
revisions, manual settings in BIOS are not required regarding DMA or
interrupts or etc. and so they might not even be available (in which case a
legacy device might not be usable in a newer computer, such as is the case
with the for now and ever-more lack of ISA support). For the curious, PCI
relates to the white colored slots you can plug devices into, where as ISA
were the old black colored slots that don't come in new computers anymore.
If you operating system settings won't allow DMA to be used for a device, it
doesn't hurt to see if by some chance your BIOS has provisions for manual
settings. It could hurt, however, to set something in BIOS incorrectly ...
hurt to the point that a computer will not boot or HDD structure gets messed
up, so if in doubt about BIOS settings, take it to a computer service shop.
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