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.

The original CMD640 has data corruption bugs, some of which remained in CMD646.^[1] The data corruption bug is similar to the bug affecting the contemporaneous PC Tech (a subsidiary^[2] of Zeos) 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.^{[citation needed]}