- The x86 BIOS: Its Limits and Capabilities
- 16- and 32-Bit Code
- The BIOS as Driver for DOS
- Modern Uses of the BIOS
- What BIOS Do You Have?
- Add-On Card BIOSs
- Video BIOSs
- Boot BIOSs for SCSI and Networking
- Additional BIOSs
- BIOS Updates
- EIDE and SCSI Hard Disk Handling
- Understanding CHS Geometry Limits
- Getting Around the 1024-Cylinder Limit
- Common BIOS Disk Utilities
- The Handoff to the OS
Common BIOS Disk Utilities
BIOSs (both motherboard BIOSs and those on SCSI host adapters) often contain utilities to help you perform routine and non-routine maintenance on hard disks. Some of the more common utilities include
Disk detection and configurationYou can usually tell the BIOS to auto-detect hard disks, either once or at every boot. Many BIOSs then enable you to specify a CHS translation scheme. Figure 3.4 illustrates one BIOS's hard disk detection and translation options. For SCSI disks, you might have an option to support disks larger than 1GB. If enabled, such an option usually moves the 1024-cylinder limit to approximately 8GB, though on some host adapters the limit is only pushed up to 2GB or some other value. Very old SCSI host adapters use physical switches or jumpers to set these options, rather than a BIOS configuration utility.
Data transfer methodsModern hard disks often let you transfer data in large chunks, as in the Multi-Sector Transfers and 32 Bit I/O options shown in Figure 3.4. Options such as this often speed up transfers. Other options might relate to direct memory access (DMA) mode transfers, which allow the disk controller to send data directly to memory rather than going through the CPU; and the level of the AT attachment (ATA) commands used (the higher the level, the better). For the most part, a BIOS will set itself up for optimal transfer performance for any given drive. These settings can often be overridden by OS drivers.
Figure 3.4 BIOSs enable you to adjust hard disk options by using menus or following onscreen prompts.
Disk formatting utilitySome BIOSs, particularly for SCSI disks, include an option to perform a low-level format on the hard disk. This format rewrites the information the disk uses to locate individual sectors and often erases every sector on the disk. You should therefore use such an option only when you want to completely erase a disk. The main reason to do a low-level format is if the disk has developed a few bad sectors; the formatting process will map these sectors out, so that they're no longer used by the drive. A low-level format can take several minutes, or even hours, to complete, so don't do it unless you have some time to spare.
If a drive develops a few bad sectors, this might be a sign that it's developing serious problems. Rather than cover over the problem by doing a low-level format, you might want to replace the drive.
Sometimes utilities such as these come as a separate utility program rather than as BIOS routines. This is particularly true of disk format utilities. Such utility programs generally run from DOS, so you might want to ensure that you have a working DOS boot floppy in case you need to run the utility program in the future. You can create a DOS boot floppy from a DOS installation by typing FORMAT /S A: or SYS A: on an already formatted disk.