Answer
The 915P-A V1.2A MB South Bridge is ICH6 that only supported UDMA5 (ATA100) for IDE device. In the CMOS Setup menu, the BIOS detects SATA HDD to IDE HDD UDMA6 mode, but in real mode (Post screen / Windows XP), it’s UDMA5 due to ICH6 supported Mode. The PIO, DMA and UDMA concepts are exclusively for IDE ATA/TAPI drives. These terms do not apply for Serial ATA drives. The fastest ATA mode is UDMA 6 (133 MB/s) while Serial ATA technology can transfer data up to 150 MB/s. Operating systems and other applications may recognize Serial ATA drives as UDMA5. However, this does not reflect the correct transfer rate of your drive. From Sandra 2005 test result, you can find the SATA HDD could be recognized to UDMA6 mode, but the real mode is UDMA5. Actually, UDMA5/6 and SATA model performance is the same when we use the HDD performance test utility to test it (Sandra 2005 or something else). We also found all the other brands M/B in the market that has the same technology.
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