This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
There appears to be an awful lot of confusion about this subject, partly due to some unhappy terminology.
In the most literal sense, no ATA(-2,-PI) drive will allow 32-bit access. Data is transferred to and from the drive over a 16 bit bus. However, many local bus interfaces are capable of combining two 16-bit words into a 32-bit doubleword when reading data from the disk, and the reverse when writing. This way, data transfer between the CPU and the interface can be done in 32-bit chunks. This is often called '32-bit access', although '32-bit host bus transfers' would be a better name.
With 32-bit host bus transfers, more efficient use is made of the computer's bus and CPU. On the other hand, these are seldom the bottleneck, so don't expect miracles from this feature. Windows' 32-bit disk and file access are completely unrelated issues and the subject of question 8.10 and 8.11.