Everybody knows this already - the Intel PCIsets 430 FX, HX VX and TX include the PIIX (PCI ISA IDE XCELERATOR), which is capable of transfering data between an EIDE device and the memory via DMA (Direct Memory Access) by using Bus Mastering. This means that data is transferred (more or less) directly from the HDD to main memory without using very many CPU resources. Also the new Multi Word DMA Modes introduced by the EIDE/Fast ATA specifications are able to transfer data just as fast as the new PIO (Programmed Input/Output) Modes. The advantage of using the Bus Master DMA is that it uses less CPU resources than PIO and therefore it's of particular benefit in multitasking environments, where the CPU can work on a different program while data is transferred to or from the HDD.
However, the way of the data from the harddisk into the memory is devided into two parts: From the drive to the chipset's EIDE interface and from the EIDE interface into the memory. The BIOS of the PC sets the EIDE interface of the chipset to use busmaster transfer between the drive and the interface. The busmaster driver is needed, to initiate the DMA transfers between the interface and the memory. The busmaster driver can switch on the DMA transfer between the drive and the interface, but if this isn't properly supported by the BIOS it will use PIO mode instead. However, the transfer from the EIDE interface into the memory can still use DMA.
If you want to use this feature, you'll need a driver for your specific OS. There is no option in any BIOS so far to enable or disable it, so don't bother about your BIOS, you'll just need the right driver. Since Windows 95 seems to be the most popular OS so far, here the...
Windows 95 IDE Bus Master DMA Drivers
You can find any busmaster driver available at BM Drivers.com
In the new so called Windows95 service release 2 (which is only sold as an OEM-product to PC manufacturers) you now have a DMA capable driver included (name is still ESDI_506.pdr). DMA mode can be switched on or off in the drive proberty screen in system manager.
Windows98 supports Busmastering for most Chipsets
Problems With The Bus Master DMA Drivers Under Windows 95
The most common problem with these drivers I came across so far are with an ATAPI CD-Rom drive or a NON EIDE HDD, which also is connected to the EIDE interface and isn't recognized by the driver. In other words: You install the driver and your CD-Rom and older harddrive have disappeared .
We also have all come across the delayed Windows 95 boot up problem, which seems to annoy a lot of impatient people. If you have a look into the System Manager you'll find a not working second IDE port in case you haven't connected anything to it. The solution to this problem is the same.
One very good answer to this problem is to get the DMA driver working on one EIDE port and the default PIO driver on the other (to connect the CD-Rom or old hard drives or to get rid of this non functioning second IDE port).
After installing the Bus Master Driver you simply have to change the registry (always back up registry before changing it !!!!!):
- find HKEY_LOCAL_MACHINE/System/CurrentControlSet
- there should be four subdirectories 0000 -0003
- find the one where DriverDesc is something like "Primary Bus Master IDE controller " or "Secondary Bus Master IDE controller ", according to the port you want to change (should be 0002 or 0003).
- in this subdirectory you change PortDriver from "ideatapi.mpd " to "ESDI_506.pdr "
- if you want to, you can change DriverDesc to something like "Standard IDE/ESDI controller ", to make it look more correctly in your Systems Manager
Now this EIDE port is using the default PIO driver and you easily can use CD-Roms or non EIDE hard drives on this port.
A different solution to this problem seems to be keeping the data wires to the HDDs/CD-Roms as short as possible, which does the trick Mount the drives properly, they should be grounded !
Another trick that may shorten the startup time, is to start Windows95 in safe mode and delete all drives in System-Manager. Don't worry, with the next start up of Windows95 they will be recognized again.
Here a new suggestion from Gerwin de Wit . He has two HDDs, both of which are connected to his primary IDE port and an ATAPI CDRom on the second port configured as SLAVE - so there's only a slave drive running at his second IDE port! This obviously works just fine with the Bus Master IDE Driver - when the CD-ROM was configured as a Master, it would not work. His CDRom is a Teac CD-56E. I just wonder what happens if you add a new 3rd HDD and configure it as 2nd Master...
- Cheers Gerwin !
Who ever has got problems with his PIIX3, coming with the Intel chipsets 430HX, 430VX and 440FX, should have a look at this Intel Page.