the 3B21D is emulated faster on a modern SPARC than a 3B21D microcomputer's processor actually runs as measured in MIPS. The most difficult thing about having the emulator is acquiring a DMERT/UNIX-RTR hdd image to actually run. The operating system for the 5ESS is restricted to a few people, employees and customers of the vendor, who either work on it or write the code for it. Having an image of a running system, which can be obtained on eBay, pulled from a working 3B21D, and imaged to a file or put into an Ultra60 or SPARCstation-5, provides the resources to attempt to run the UNIX-RTR system. The uname -a output of the Bourne shell running UNIX-RTR (Real-time Reliable) is: # uname -a <3B21D> <3B21D> Though on 3B20D systems it will print 20 instead of 21, though 3B20Ds are rare, nowadays most non-VCDX 5ESSs are 3B21D hardware, not 3B20D (although they will run the software fine). The 3B20D uses the WE32000 processor while the 21 uses the WE32100. There may be some other differences, as well. One thing unusual about the processor is the direction the stack grows: up. Manual page for falloc (which may be responsible for Contiguous or eXtent file space allocation): FALLOC(1) 5ESS UNIX FALLOC(1) NAME falloc - allocate a contiguous file SYNOPSIS falloc filename size DESCRIPTION A contiguous file of the specified filename is allocated to be of 'size' (512 byte) blocks. DIAGNOSTICS The command complains a needed directory is not searchable, the final directory is not writable, the file already exists or there is not enough space for the file. UNIX-RTR includes an atomic file swap command (atomsw, manual page below): ATOMSW(1) 5ESS UNIX ATOMSW(1) NAME atomsw - Atomic switch files SYNOPSIS atomsw file1 file2 DESCRIPTION Atomic switch of two files. The contents, permissions, and owners of two files are switched in a single operation. In case of a system fault during the operation of this command, file2 will either have its original contents, permissions and owner, or will have file1's contents, permissions and owner. Thus, file2 is considered precious. File1 may be truncated in case of a system fault. RESTRICTIONS Both files must exist. Both files must reside on the same file system. Neither file may be a "special device" (for example, a TTY port). To enter this command from the craft shell, switching file "/tmp/abc" with file "/tmp/xyz", enter for MML: EXC:ENVIR:UPROC,FN="/bin/atomsw",ARGS="/tmp/abc"-"/tmp/xyz"; For PDS