PXE target boots to USB drive instead of Hard Drive

Document ID : KB000009476
Last Modified Date : 14/02/2018
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When a PXE enabled PC with no active OSIM Configuration boots and communicates with a Boot Server, It tries to boot the USB connected HD instead of the internal Drive 


On all PCs the boot device order is as follows. 


Onboard NIC 

Internal HDD

Optical Device

USB Storage Device


All CA Client Automation 12.5 and aboveOS ANY?Only reported on the following DELL PlatformsOptiPlex 790Latitude E6420

Whilst a solution would need to come from the BIOS vendor there is a workaround that will resolve the issue within the product. 

There is a configuration option that can be defined that causes bootHD to pass control back to BIOS rather then booting the HD direct. 

.....DSM/Scalability Server/OSIM/ManagedPC/Server 

Name = Let PXE choose the boot sequence

This value determines the behavior of a PXE client machine when receiving the order to boot locally (boothd). If set to 'True'(1) control is returned to the BIOS to proceed to the next device in the boot sequence. If set to 'False'(0) the client directly boots from the hard disk.

The default value is 'False'.

Additional Information:


When a PC PXE with no active OSIM configuration is started the boot server provides the bootfile boothd which tells the PXE computer that there is no OSIM job and to continue booting the HD

Boothd contains code that causes the PC to boot the first physical hard Drive as determined by the interrupt 13h address.



This obviously bypasses the remainder of the boot order defined in BIOS.

As these devices boot to the USB device the only explanation can be that the BIOS is assigning the 80h address to the USB device instead of the physical Hard Drive.