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Beautiful Architecture by Diomidis Spinellis, Georgios Gousios

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File System

Tandem uses the term file system to mean the access to system resources that can supply data (“read”) or accept it (“write”). Apart from disk files, the file system also handles devices, such as terminals, printers, and tape units, and processes (interprocess communication).

File Naming

There is a common naming convention for devices, disk files, and processes, but unfortunately it is complicated by many exceptions. Processes can have names, but only I/O processes and paired processes must have a name. In all cases, the file “name” is 24 characters long and consists of three 8-byte components. Only the first component is required; the other two are used only for disk files and named processes.

Unnamed processes use only the first 8 bytes of the name. Unpaired system processes, such as the monitor or memory manager, have the format shown in Figure 8-7.

Name format for unpaired system processes

Figure 8-7. Name format for unpaired system processes

Unpaired user processes have the format shown in Figure 8-8.

Name format for unpaired user processes

Figure 8-8. Name format for unpaired user processes

The combination CPU and PIN together forms the process ID, or PID. The PIN is the process identification number within the CPU. This limits each CPU to 256 processes.

Real names start with a $ sign. Devices use only the first 8 bytes, and disk files use all three components. ...

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