Since yesterday my computer seemed to really be chugging along.  This seems to happen about once a year.

My primary HD was reading at only 3 MB/s instead of the usual 60 MB/s or so!

Why? As crc errors happen over time windows will keep track of the accumulation and will eventually turn off DMA and use the slower PIO mode. (Here’s a windows article about it..)

Is your drive slowing down?  Use the great (and free) utility HD-Tune to check it.

The fix is very simple, just remove all your IDE ATA/ATAPI controllers from the control panel and reboot.  They will be re-added at full speed.