by the ">" symbol. Typically the system disk will be housed in the same module as the CPU, #m1, so a system file for a VOS cluster would be referenced as (%system)#m1_d01>system>devices.table VOS disk allocation and memory is organised in "blocks", each block being 4,096 bytes. Memory takes the form of RAM or paging. VOS systems support paging partitions and paging files. In modern versions of VOS, paging files can be created dynamically by the SysAdmin (but not removed without a reboot). These paging files can in theory consist of more than one extent (which is viewed by the kernel as a mini-paging partition) which may or may not be contiguous. However, non-contiguous extents are NOT recommended as they greatly increase disk activity. Admin should create the largest possible extent for the paging files as early as possible after the system has been booted. File system security VOS supports write, read, execute, and null (no) access to all files, directories and devices (although directories and files have slightly different access lists). Access can be assigned to users, groups, or the world. Only read access is required to run an executable program, provided that the user has "status" access for the directory in which that program resides. VOS inherited access control lists from Multics and also implements directory access control lists. If a file does not have an access control list, the containing directory's default access control list applies. Access to devices is typically controlled by creating a file which is linked to the device by the administrator. (This may be true in OpenVOS, but does not apply to the original operating system.) Access is then given to this file, and this sets the access on the device. Open StrataLINK VOS has always been a network-aware operating system. Virtually every system call in the native API has a parameter that determines what computer the operation affects. If the operation isn't local, it is redirected to the target computer via remote subroutine call. For example, file names are parsed to indicate which computer the file resides on. The StrataLINK networking model has a two level hierarchy for naming computers: Each computer is called a module and modules are aggregated into systems. Each system is administered as a unit. In other words, all of the modules in a system are aware of all the disks and hardware devices on that system. The result