There are actually a bunch of ports. For ide non lba mode it's like this:
Port, reading, writing (base 40h)
40,Rd data,Wr data
41,error,features
42,sector count, sector count
43,sector number, sector number
44,cyl low, cyl low
45,cyl high, cyl high
46,select head/drive, select head/drive
47,status, command
Matt