Enhanced Integrated Drive Electronics (EIDE) The EIDE interface was developed to overcome many of the limitations of the IDE interface. As we saw in  chapter  7,  EIDE  provides  the  capability  for addressing fixed disks with over 540 MB of storage capacity. EIDE also provides faster data transfers and the ability to use a CD-ROM drive in an EIDE system. Small Computer Systems Interface (SCSI) The  Small  Computer  Systems  Interface  (SCSI)  is really a systems level interface, not just a disk interface. SCSI (pronounced  scuzzy) uses a host adapter that plugs into the computer. The SCSI has eight I/O ports. One is dedicated as the interface between the host computer and the adapter. The other seven ports are available for other device controllers, such as disk drives, CD-ROM readers, and digital scanners. The SCSI is a smart interface.  When the host computer requests data from a device connected to the SCSI, the SCSI will disconnect itself to free up the computer while it processes the request. The SCSI is capable of transferring data at up 100 megabits per second. FORMATTING FIXED DISKS Fixed disk systems operate in much the same manner as the floppy disks and the disk memory set. Before a new fixed disk drive can be used in a personal computer, it must be formatted. The formatting of a fixed  disk  is  performed  by  two  or  three  separate operations. These are as follows: Q Low-level format l Creating a DOS partition .  High-level  format Low-Level Format The  low-level  format  program  writes  the  tracks  and sectors on the disk. Low-level format programs vary according  to  the  type  of  drive  and  controller.  Many controller  manufacturers  now  include  the  low-level format program in a ROM on the controller. You can access this program by using the DOS DEBUG routine. Refer to the controller’s documentation to find the starting address for the format program. When you install and format a new fixed disk drive, it is extremely important to enter the defective tracks from the list supplied by the manufacturer. These bad tracks are usually listed on a label on the drive, with another hard copy supplied with the documentation. When the low-level format program is executed, it will mark any bad tracks with a checksum error that will prevent these tracks from being used for data storage. In addition, the low-level format program will check all areas of the disk to see if any additional bad tracks are detected. If you are formatting a new disk, only the tracks on the manufacturer’s list should be bad. If you are reformatting an older disk and find that additional tracks are listed as bad, the disk is showing signs of severe  damage  and  should  be  replaced. CAUTION DO NOT run a low-level format program on an IDE drive. Serious damage could result by trying to low-level format this type of drive. 10-28 There are two additional terms you need to be familiar with to low-level format or troubleshoot fixed disks. These are write precompensation and reduced write current. Write precompensation and reduced write current are also used in some disk memory sets. Write  Precompensation — Write precompensa- tion is used to prevent problems that can occur when data is written on the higher numbered cylinders. A disk is divided into sectors and tracks. Each sector can store 512 bytes of data. The sectors on the outside of the disk surface are physically larger than the ones on the inside of the disk. As data is recorded on the disk, like poles of magnetic fields are repelled away from each other and opposite poles are attracted to each other. As the heads move toward the center of the disk, the write precompensation circuitry changes the spacing of the magnetic fields. After the natural attraction or repelling of the magnetic domains is complete, the magnetic fields are in the proper place. Reduced  Write  Current  — Reduced write current also compensates for problems that can arise when writing on the inner tracks of a disk. As the system writes on the inner tracks of the disk, less current is required because the data is more densely packed. Using the same current on the inner tracks that is required on the outer tracks would cause the data to run over  each  other. Manufacturers’ data sheets included with new drives   will   indicate   what   cylinder   write precompensation  and  reduced  write  current  are