Comparison with NTFS

RAM File System is a complete, non-simplified Windows file system. Its volumes appear as ordinary local drives and behave like NTFS volumes in nearly every respect, so applications, installers and tools work on such volumes without adjustment. RAM FS volumes report themselves as NTFS because some third-party software can refuse to work with, or fall back to slower paths, when it sees an unfamiliar file system name, such as 'RAMFS'.

Similarities between RAM FS and NTFS

• Windows security: per-file permissions, ownership and inheritance, enforced on every open operation.
• Hard links, symbolic links and junctions, and reparse points in general.
• Sparse files and extended attributes.
• Network sharing: opportunistic locks and leases, so a volume can be shared over SMB.
• File locking and directory change notification, so editors, databases and build tools behave normally.
• Memory-mapped files, used by databases and many applications.
• Long Unicode names of up to 255 characters, case preserved.
• File identifiers, letting applications reopen a file by ID rather than by name.
• Volume labels, with renaming and relabelling in Windows Explorer.

Advantages of RAM FS over NTFS

• Reflink copies: copying a file within a volume is instant and takes no extra memory until one of the copies is modified. NTFS has no equivalent.
• Transparent compression with modern codecs and a choice of compression levels, applied automatically across the whole volume rather than file-by-file.
• Thin storage: memory is used only for the data actually written, so empty space inside files occupies nothing.

Not in RAM FS

A few NTFS features are absent in RAM FS. None of them fail silently: an application that requests such functionality receives a clear “not supported” answer rather than an unexpected result.

• Alternate data streams: the mark that Windows attaches to downloaded files is not retained.
• Short 8.3 file names, relevant only in ancient software.
• Encrypting File System (EFS), of limited relevance in a volume whose contents live in RAM and disappear when it is dismounted.
• Disk quotas and the change journal used by some backup and indexing tools.
• NTFS compression attribute. RAM FS has its own, automatic compression instead, set per volume rather than per file.
• Object identifiers, transactions and defragmentation, none of which are meaningful for data held in memory.
• Formatting and disk checking. As volumes are created and managed by RAM FS itself, there is nothing to format or repair.

Minor differences

• Folder nesting is limited to 64 levels.
• Volume labels may be up to 31 characters, one fewer than in NTFS.
• Empty space inside sparse files is reclaimed in 2 MB units rather than 4 KB.
• Some anti-virus and backup filters see RAM FS as a file system they do not recognise, even though the volume reports itself as NTFS.

Free space is counted differently

This is the most commonly noticed difference, and it is worth understanding what is the correct and expected behaviour.

RAM FS stores only the meaningful file contents

Empty areas within a file, and areas consisting entirely of zeros, occupy no memory. This applies equally to data written in place and to files copied onto the volume. Files of this kind are very common:

• Anything created at full size and filled in gradually: shader caches, databases, download managers.
• Disk and virtual machine images, which typically contain large unused areas.
• Test and placeholder files, and datasets padded to a fixed size.

By contrast, NTFS reserves space for the entire file regardless of its contents.

The volume space figure is the real one

The used and free space figures shown in the drive properties reflect the memory that the volume genuinely occupies. Whereas a file's own Size and Size on disk are reported the classic Windows way, so a folder can claim far more than the volume reports as used. Several gigabytes of files consisting mainly of empty segments may occupy just a few megabytes of memory. Both figures are correct: one is what the files claim, the other is the memory really in use, and the difference is free RAM that can be used instead of sitting idle. As the files fill up with data, the volume figure grows closer to the claimed figure.

These features can widen the reported space gap:

• Reflink copies share their storage, so each copy reports its full size while in reality all together they occupy little more space than one.
• Compression reduces the physical footprint, but volume capacity is deliberately counted as though nothing were compressed, so that writing to the volume can never fail unexpectedly.

For the true physical footprint, look at the memory bar along the bottom of the RAM File System main window — it shows what the volumes really occupy in RAM.