Not very easily would be my answer. (At least not without knowing the specific implementation details of a controller.)
Remember that the size of an allocation unit varies with the size of the partition. The older FAT 16 file system allocation units ranged in size from 4 sectors to 64 sectors and can have up to 2^16 allocation units (65536). (2k to 64kb per allocation unit.) The semi-modern FAT 32 file system can have up 2^32 allocation units (4294967296). That means if you want to determine how many allocation units are transfered per cycle, you will first need to know what the size of an allocation unit is on your drive. Most chipsets use the PCI bus to transfer data from the IDE drives, which is a 32 bit bus running at 33 MHz. (Be aware that 64 bit PCI slots and 66 MHz PCI slots do exist, but wouldn't be common in a typical PC.) Theoretically that means the PCI bus can transfer up to 133 Mbytes/sec. There are also multiple Ultra ATA standards (which is the standard term - EIDE was/is a Western Digital marketing term), each with different maximum transfer rates. The highest standardized rate is 100 MBytes/sec (Maxtor has a 133 MBytes/sec mode - ATA133).
