Bit #5 of word #82 of the Identify Device information block indicates whether “the volatile write cache is supported”.
Bit #5 of word #85 of the Identify Device information block indicates whether “the volatile write cache is enabled”.
Bit #1 of words 119 and 120 indicates whether “the Write-Read-Verify feature set is supported/enabled”.
If Write-Read-Verify is enabled, then this would result in slower writes because there would need to be two revolutions of the platters for each write.
Working Draft ATA/ATAPI Command Set - 3 (ACS-3):
http://nevar.pl/pliki/ATA8-ACS-3.pdf
A tool such as CrystalDiskInfo is able to report the Identify Device data (512 bytes):
http://crystalmark.info/software/CrystalDiskInfo/index-e.html
