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feat: High to low memory scanning in DOS Memory Manager and DOS UMB support - #2395
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feat: Add support for DOS Upper Memory Blocks (UMBs) in memory management Refactor UMB handling and enhance memory allocation strategies - Changed the `Umb` property in `Configuration` from init-only to settable. - Updated `DosInt21Handler` to use a new method for finding the largest free size for allocation. - Enhanced `ExtendedMemoryManager` to manage UMB requests and releases more effectively. - Refactored `DosMemoryManager` to support new allocation strategies and improved memory block management. - Introduced new methods for validating and setting memory allocation strategies. - Updated `DosMemoryAllocationStrategy` enum to clarify UMB handling. - Added integration tests for UMB functionality, including allocation strategies and error handling. - Created assembly test resources to validate UMB behavior in various scenarios. fix: Improve upper memory block release logic and enhance memory chain handling fix: Update UMB release logic and add FreeUpperMemoryBlock method for better memory management refactor: ExtendedMemoryManager to enforce non-nullable DosMemoryManager and update related constructors
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… high-memory bits
Update DOS memory initialization to set `DosSysVars.FirstMCB` and `MemAllocScanStart` from the actual conventional-memory chain head, remove the hardcoded `FirstMcbSegment` default, and adjust docs and UMB integration tests to follow the sysvars chain head.
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Description of Changes
Adds DOS Upper Memory Block (UMB) support and extends DOS memory allocation to honor the configured allocation strategy across conventional and upper memory.
Detail
--Umboption, enabled by default. UMBs are available when the option is enabled and XMS is present.Rationale behind Changes
Hopefully the new memory scan strategy will fix games such as Alone in the Dark and others that complain about not enough memory.
DOS UMB support also makes more MCBs available to DOS applications.
Testing