Disk-based OS-9 systems use a system disk to load many parts of the operating system during the system startup and to provide files frequently used during normal system operations. Therefore, the system disk is generally kept in disk drive zero ("/D0") when the system is running. Two files used during the system startup operation, "OS9Boot" and "startup" must reside in the system disk's root directory. Other files are organized into three directories: CMDS (commands), DEFS (system-wide definitions), and SYS (other system files). Other files and directories created by the system manager and/or users may also reside on the system disk. These frequently include each user s initial data directory.

The file called "OS9Boot" loaded into RAM memory by the "bootstrap" routine located in the OS-9 firmware. It includes file managers, device drivers and descriptors, and any other modules which are permanently resident in memory. A typical Microware OS-9 distribution disk's "OS9Boot" file contains the following modules: IOMAN OS-9 Input/Output Manager RBF Random Block (disk) File Manager SCF Sequential Character (terminal) File Manager Pipeman Pipeline File Manager Piper Pipeline Driver Pipe Pipeline Device Descriptor KBDVID Keyboard/video/Graphics Device Driver PRINTER Printer Device Driver DDISK Disk Driver D0, D1 Disk Device Descriptor TERM Terminal Device Descriptor P Printer Device Descriptor CLOCK Real-Time Clock Module SYSGO System Startup Process Users may create new bootstrap files which may include additional modules (see "OS9Gen" command). Any module loaded as part of the bootstrap cannot be unlinked and is stored in memory with a minimum of fragmentation. It may be advantageous to include in the OS9Boot file any module used constantly during normal system operation. This can be done with the OS9GEN command.

The directory "/d0/SYS" contains two important files: password the system password file (see "login" command) errmsg the error message file (see 4.7) These files (and the SYS directory itself) are not absolutely required to boot OS-9, they are needed if "login", "tsmon", or "printerr" will be used. Users may add other system-wide files of similar nature if desired.

The file "/d0/startup" is a shell procedure file (see 4.6) which is automatically processed immediately after system startup. The user may include in "startup" any legal shell command line. Often this will include "setime" to start the system clock. If this file is not present the system will still start correctly but the user must run the SETIME command manually.

The directory "/d0/CMDS" is the system-wide command object code directory, which is normally shared by all users as their working execution directory (see 3.7). If "shell" is not part of the "OS9Boot" file, it must be present in this directory. The system startup process "sysgo" makes CMDS the initial execution directory.

The directory "/d0/DEFS" is a directory that contains assembly language source code files which contain common system-wide symbolic definitions, and are normally included in assembly language programs by means of the OS-9 Assembler "use" directive. The presence and use of this directory is optional, but highly recommended for any system used for assembly language programs. The files commonly contained in this directory are: OS9Defs main system-wide definition file RBFDefs RBF file manager definition file SCFDefs SCF file manager definition file Systype System types definition file

The system disk is not usually removed while the system is running, especially on multiuser systems. If it is, the "chx" and "chd" (if the working data directory was on the system disk) commands should be executed to reset the working directory pointers because the directories may be at different addresses on the new disk, for example: chx /d0/cmds chd /d0 In general, it is unwise to remove a disk and replace it with another if any paths are open to files resident on the disk. It is dangerous to exchange any disk if any files on it are open in WRITE or UPDATE modes.

To make a system disk, the following steps must be performed: The new disk must be formatted. The "OS9Boot" file must be created and linked by the "OS9Gen" or "Cobbler" commands. The "startup" file must be created or copied. The CMDS and SYS directories and the files they contain must be copied. Steps 2 through 4 may be performed manually, or automatically by any of the following methods: By a shell procedure file created by the user. By a shell procedure file generated by the "dsave" command By the "backup" command