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Writing a New Boot Block on the System Disk  



Block 0 on a system disk is the boot block. It contains the size and location of the primary bootstrap image, which is used to boot the system.

On VAX systems, the primary bootstrap image is VMB.EXE.

On Alpha systems, the primary bootstrap image is APB.EXE.

Certain processors must read the boot block to obtain the location of the primary bootstrap image. Processors that read a boot block include the following ones:

To determine if your system reads the boot block, check one of the following manuals:

If you suspect that the boot block on the system disk is invalid, you can write a new boot block using the Writeboot utility (WRITEBOOT). The following actions might cause a boot block to become invalid:

You must have LOG_IO privilege to use the Writeboot utility.

How to Perform This Task

On VAX systems, follow these steps to use the Writeboot utility:

  1. To start the Writeboot utility, enter the following command:
    $ RUN SYS$SYSTEM:WRITEBOOT
  2. The procedure displays the following message:
    Target system device (and boot file if not VMB.EXE):?
    On VAX systems, VMB.EXE is the default bootstrap image. Enter a response in the following format:device:[VMS$COMMON.SYSEXE]VMB.EXE; Use the device name format described in the upgrade and installation documentation for your processor. If you want to boot using a bootstrap image other than the default, you must specify the full file specification of the image, including device and directory.
  3. The procedure displays the following message:
    Enter VBN of boot file code (default is one): 
    Ordinarily, the boot code is located at virtual block number (VBN) 1 of the bootstrap image. Press Return to accept the default value of 1.
  4. The procedure displays the following message:
    Enter load address of primary bootstrap in HEX (default is 200): 
    The load address is the location in memory (specified in hexadecimal notation) to which the system loads the bootstrap image. Ordinarily you copy the bootstrap image to address 200. Press Return to accept the default value of 200.
  5. The Writeboot utility writes the information you specified to the boot block (block 0) on the system disk.

On Alpha systems, follow these steps to use the Writeboot utility:

  1. To start the Writeboot utility, enter the following command:
    $ RUN SYS$SYSTEM:WRITEBOOT
    The procedure asks you whether you want to write the VAX portion of the boot block:
    Update VAX portion of boot block (default is Y):
  2. Enter NO.
  3. The utility displays the following prompt:
    Update Alpha portion of boot block (default is Y):
    Press Return to accept the default value of Y.
  4. The utility prompts you for the Alpha bootstrap image:
    Enter Alpha boot file:
    On Alpha systems, APB.EXE is the default bootstrap image. Enter a response in the following format:device:[VMS$COMMON.SYSEXE]APB.EXE; where device specifies the device name of the system disk.
  5. The Writeboot utility writes the information you specified to the boot block (block 0) on the system disk.

On VAX and Alpha systems, the Writeboot utility might display one or more of the following error messages:

Example

On VAX systems, the following example writes a boot block on a system disk:

$ RUN SYS$SYSTEM:WRITEBOOT
Target system device (and boot file if not VMB.EXE):? DUA0:[VMS$COMMON.SYSEXE]VMB.EXE
Enter VBN of boot file code (default is one):[Return] 
Enter load address of primary bootstrap in HEX (default is 200): [Return] 
On Alpha systems, the following example writes a boot block on a system disk:
$ RUN SYS$SYSTEM:WRITEBOOT
Update VAX portion of boot block (default is Y): N
Update Alpha portion of boot block (default is Y): [Return] 
Enter Alpha boot file: DUA0:[VMS$COMMON.SYSEXE]APB.EXE; 

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