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What is the difference between DMA and PIO [?] - 8/5/2002 6:56:28 PM   
Laffin Assassin

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Question :-
What is the difference between DMA and PIO [?]

IDE hard disks are accessed in one of two ways: PIO (Programmed Input/Output) or DMA (Direct Memory Access). There are 5 different PIO modes, from slowest (0) to fastest (4). The highest is normally used when the drive is automatically detected. Best check in your BIOS.

PIO: Traditionally, the transfer method for IDE devices has been PIO where data is transferred to/from IDE devices using the CPU. PIO requires a relatively large amount of dedicated CPU time (40%), especially when transferring large amounts of data to/from hard disk drives. Transfer speeds may be in the region of 16MB/sec.

DMA: DMA allows for the transfer of data to/from IDE devices without heavy dependence on the CPU and increases transfer speeds. Its operation requires a Bus Master driver.(It uses Bus Master IDE (BM-IDE) logic contained within the PIIXn IDE controller. The PIIXn IDE controller acts as a PCI Bus Master on behalf of IDE DMA slave devices, performing DMA transfers to/from devices on primary or secondary IDE channels).

UDMA: Newer Intel chipsets (PIIX3 and later) can perform fast DMA transfers using the UltraDMA/33 hardware interface. UDMA is an abbreviation of Ultra DMA. Its operation requires its own Bus Master driver. Speeds of 33MB/sec can, theoretically, be achieved.

These can be a boost to speed - but mostly under certain circumstances. Disk-intensive applications will benefit from UDMA's increased throughput, and applications stored on the UDMA hard drive will load faster. Bootups should be faster.

I hope this Clears things Up !!!

Laffin Assassin

New Hardware & Software isn't released it's allowed to escape !!!
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