The 3.5-Inch Disk Densities and Coercivities The 3.5-inch disks are constructed and rated in much the same way as 5.25-inch disks. Table 10-6 shows  the  densities  and  required  coercivities  for 3.5-inch  disks. USING LOW-DENSITY DISKS IN HIGH-DENSITY  DRIVES A high-density drive will read a low-density disk with no problems. A problem occurs when you try to use a high-density drive to write on a low-density disk that  was  previously  used  in  a  low-density  drive. Referring back to table 10-5, you see that the track width on a 360K disk is approximately .33 mm. The tracks written by a 1.2M drive are approximately .16 mm. When you try to overwrite data that was originally produced by a 360K drive, you are writing a little skinny track through the middle of a wider track. If you take this disk back to a 360K drive, the bigger heads will not only try to read the skinny track but will also read some of the data that was supposed to have been overwritten by the high-density drive. The only way to avoid these read errors is to format anew (unformatted) 5.25-inch disk in the high-density drive. Refer to your DOS user’s manual for the proper command to format a 5.25-inch disk for 360K with a 1.2M drive. Use this disk to write any data that you want to transfer to the 360K drive. Another problem can occur if you format a 360K, 5.25-inch disk as a 1.2M disk. DOS will allow this operation. Again referring back to table 10-5, you see that a 1.2M disk requires twice as much write current as a 360K disk. Writing this strong magnetic field on the iron oxide of a 360K disk will cause the bits written on  the  disk  to  change  position.  That  is,  adjacent opposite magnetic poles will migrate toward each other, and similar magnetic poles will migrate away from each other and your data will be lost. The 3.5-inch drives do not have this problem, since the 1.44M disks have a high-density medium indicator hole in the disk case. If you try to format a 720K, 3.5-inch disk as a 1.44M disk, DOS generates an error message. A  high-density  disk  can  never  be  used  in  a low-density drive. The low-density drive cannot generate the required write current to write data on a high-density disk. FLOPPY DISK DRIVE INSTALLATION AND CONFIGURATION The physical installation of a floppy drive in a personal  computer  is  fairly  simple.  Remove  the computer case, place the drive in the bracket supplied in the installation kit, and install the drive in the computer. Configuring the drive for the computer is a bit more complicated. Most  disk  controller  cards  used  in personal computers can control two floppy drives and two fixed disk drives. The floppy drives are usually daisy chained on the same cable to a single connector on the disk controller card. The drive electronics card has several jumpers including the following: Drive select jumper Terminating resistor Disk  changeling/ready  jumper Media sensor jumper Drive Select Jumper The drive select jumpers are located on the drive electronics card. They are usually labeled DS0, 1, 2, and 3. These designations are not standard and some manufacturers  use  different  labels  or  numbers.  The drive select jumpers could be labeled DS1, 2,3, and 4. Before  you  can  properly  configure  the  drive address, it is important to check the floppy drive cable. The cable has three connectors, one at each end and one in  the  middle.  Carefully  examine  the  cable  to  determine if pins 10 through 16 are twisted near the end of one Table  10-6.—The  3.5  Inch  Disk  Densities  and  Coercivities 10-11