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CMD640, the California Micro Devices Technology Inc product 0640, is an IDE interface chip for the PCI and VLB buses. CMD640 had some sort of hardware acceleration: WDMA and Read-Ahead (prefetch) support.
CMD Technology Inc was acquired by Silicon Image Inc. in 2001.
Hardware bug
The original CMD640 has a data corruption bug. The data corruption bug is similar to the bug affecting the contemporaneous PC Tech RZ1000 chipset. Both chipsets were used on a number of motherboards, including those from Intel.
Мodern operating systems have a workaround for this bug by prohibiting aggressive acceleration mode and losing about 10% of the performance.
References
CMD640 Wikipedia(Text) CC BY-SA