That doesn't make any sense. Create a file, memory-map it, bam, you have RAM performance with "filesystem semantics". (There is NO overhead associated with me

That doesn't make any sense. Create a file, memory-map it, bam, you have RAM performance with "filesystem semantics". (There is NO overhead associated with memory-mapping a file on a ramdisk in the Linux kernel.) Probably what they're referring to is something more along the lines of replacing SCSI or NFS with a protocol that is a better match for the random access patterns used to access in-memory structures. (Hence their 64-byte I/O size; that is equal to a cache line on Intel architectures.)