Floppy disks have only one boot sector, but hard disks may have more than one because each partition on a hard drive has its own boot sector. The first boot sector on the entire hard disk is called the master boot record (MBR). It is the only boot sector loaded from the hard drive by the ROM BIOS. The MBR contains a small loader program and a partition table. If the standard DOS MBR is used, it loads the boot sector from the active partition and then passes control to the boot sector. Thus, both the MBR and the active partition’s boot sector are involved in the boot process. Figure 1.1 shows how the boot process flows from the BIOS to the MBR and then to the partition’s boot sector. This figure assumes a DOS MBR and a Linux loader in the boot sector of the active partition. Alternatively, the Linux loader can be installed in the MBR to eliminate one step in the boot process. Figure 1.1: The boot process flow Note Appendix A, “Installing Linux,” discusses the pros and cons of placing the Linux loader in the MBR. The BIOS may introduce some limitations into the Linux boot process. The Linux kernel can be installed anywhere on any of the disks available to the system, but if it is outside of those limits, the system might not be able to boot. The Linux loader depends on BIOS services. Some versions of BIOS only permit the loader to access the first two IDE hard drives: /dev/hda and /dev/ hdb. Additionally, in some cases, only the first 1024 cylinders of these disks can be used when booting the system. These limitations are at their worst on old systems. New systems have two IDE disk controllers that provide access to four disk drives, and these controllers address up to 8GB of disk storage within the 1024-cylinder limit. A very old system might address only 504MB in 1024 cylinders! For a server installation, this is not a real problem. Because servers do not dual-boot, everything can be removed from the disk, and the Linux boot files can be installed in the first partition without difficulty. A desktop client is a different matter. Most desktops have Microsoft Windows installed in the first partition. If there is available space within the first 1024 cylinders on the first disk drive, use fips to create empty space and install the Linux boot partition there. (Partitioning is discussed in detail in Appendix A.) Otherwise, a client system that dual-boots is forced to use one of the following methods: 13
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