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Technical issues deploying 32-bit operating systems to modern hardware

Technical issues deploying 32-bit operating systems to modern hardware

WinPE technical limitations – Memory Allocation

The UIU functions within WinPE in order to accomplish the daunting task of providing drivers on-the-fly to any make/model of business class PC. In order to accomplish this, the UIU requires access to the registry hive of the target PC from within WinPE. Occasionally, situations present themselves wherein the limitations of hardware architectures and components conspire to prevent proper execution of processes in WinPE.

Problem Description:
When attempting to mount an offline registry hive for a 32-bit OS image (at least through Win10 1703), (which requires WinPEx86), on hardware that has more than 4Gb of RAM installed, the allocation of memory blocks can be insufficient to mount the entire registry hive which causes part of the registry to be written to memory locations that cannot be properly addressed. Upon dismounting the offline registry hive, the part of the hive that was written to those locations will be truncated which results in a corrupted registry, and a BSOD upon reboot. The issue is seen on primarily (but not limited to) newer, 64-bit designed hardware.

What is really going on?
In particular instances, the following variables may combine to affect the mounting of an offline 32-bit OS registry hive into RAM while operating in WinPE:
  • RAM type
  • RAM quantity
  • RAM configuration
  • RAM block utilization

In effect, if there are insufficient contiguous blocks of RAM to hold the mounted offline registry hive, the data is truncated and no error is presented at the time. After reboot, when windows attempts to mount the registry, the corrupted registry causes a system halt and subsequent BSOD. In the case of the UIU, the truncated mount also inhibits the UIU’s ability to determine necessary details of the target machine required to function as designed, culminating in a failed UIU-prepared deployment of the 32-bit OS to the target hardware.

This is a known issue with WinPE:

Win2008R2/Win7: STOP 0xF4 during Task Sequence / OS Deployment

"This process is sometimes a problem when using an x86 boot image. Basically because WinPE has no page file, WinPE relies completely on what physical memory is available. The end result is that memory in WinPE gets very fragmented. With x64 WinPE this is not a big deal on most modern PCs because there is a lot of memory available. However with x86 boot images, there is a limit of how much memory can be addressed (around 3GB) regardless of how much memory the PC actually has. The end result is that when the memory gets very fragmented with an x86 boot image, there is less of a chance of there being a piece of contiguous memory that large enough to hold the registry that needs to be mounted. In these situations, when the registry gets mounted, it gets corrupted and part of the registry basically gets chopped off."

In the instances where this issue is encountered, given the limitations of the x86 architecture, the UIU can only offer the following resolutions at this time:

Potential Resolutions:
  • Remove all but 4Gb RAM from the offending hardware
  • Utilize native SCCM driver inclusion technology with customized UIU driver packages (provided by UIU Support)
  • Install/deploy a 64-bit OS version

Please contact UIU Support for additional details.

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