When the Hard Disk Emulation is on, the RAM Disk application emulates a disk that conforms to the SCSI standard. In a Windows environment, this can make the RAM Disk appear just like any other SCSI disk drive, complete with partitions, a drive letter and the ability to be managed through standard Windows disk management tools. This type of disk is highly compatible with various software, as it emulates a well-known standard. Emulating a SCSI interface can introduce some overhead in terms of CPU and memory usage, although this is generally minimal.
When the Hard Disk Emulation is off, the RAM Disk application emulates a so-called Direct I/O disk. In the Direct I/O approach, the RAM Disk app bypasses the standard disk interface layers and interacts directly with the operating system's I/O subsystem. Because Direct I/O bypasses some layers of the operating system I/O stack, it can offer better performance in some scenarios. However, such disks may not be as broadly compatible with various types of software or as easily managed through native operating system tools.
The choice between these two approaches depends on your specific needs. In general, it's best to start with a Direct I/O disk, i.e. without Hard Disk Emulation, as it offers the highest possible performance and reasonably good compatibility. If you experience any issues with other programs, mainly third-party disk tools, then you can enable Hard Disk Emulation and see if it resolves those issues.