SQLServer is super Win32 specific, even to the extent of using undocumented Windows APIs (I think the canonical example is NtReadFileScatter and NtWriteFileScat

SQLServer is super Win32 specific, even to the extent of using undocumented Windows APIs (I think the canonical example is NtReadFileScatter and NtWriteFileScatter, which are more flexible than the documented ReadFileScatter and WriteFileScatter wrappers; I wouldn't be surprised if it uses many more undocumented calls). SQLOS isn't an abstraction layer over the operating system necessarily. It's more of an abstraction over the _machine_ that allows scaling between 8GB and 512+GB of RAM, 4 to 64+ cores, etc. That said, since SQLOS does handle all memory management and file I/O for SQLServer, it probably did make porting slightly easier.