livingcomputermuseum.pdp7-unix/src/sys/NOTES.md

PROCESSES

uid -1 is superuser

process 1 is "init", runs as superuser

DISK

RB09: Burroughs fixed head disk (same hardware as RD10!)

64 word sectors; 80 sectors/track; 100 tracks/surface; 2 surfaces
8000 sectors/surface
one surface reserved for backup

512,000 words per surface: 1,024,000 characters!!!

first disk block is copy of "system data"
        contains time, free block information, process (user) list?!!

12 word inodes (5 per block)
710 sectors of inodes (max 3550 files)

inode format

   i.flags
        400000  free?? (checked/toggled by icreat)
        200000  large file
        000040  special file
        000020  directory
        000017  can be changed by chmod.
            10  owner read
            04  owner write
            02  world read
            01  world write
   i.dskps      7 block numbers (all indirect blocks if "large file")
   i.uid        owner
   i.nlks       link count
   i.size       size (in words?)
   i.uniq       unique value assigned at creation

directory files can (only) be truncated by superuser

directory node (dnode) format

   d.i          i-number of file
   d.name       four words, space padded
   d.uniq       i.uniq value of file

i numbers

  1     core file?? (written by "sys save" or bad system call)
  2     "dd"??? "root" directory
  3     "system"??? default process cdir, must contain "init", "dd"

  6     "ttyin" special file
  7     "keyboard" (graphic-2) special file
  8     "pptin"?? (paper tape reader) special file
  10    "ttyout" special file
  11    "display" (graphic-2) special file
  12    "pptout" (paper tape punch) special file