Merge pull request #37 from philbudne/master

add src/sys/NOTES.md: notes on disk format and other kernel details

src/sys/NOTES.md

@@ -0,0 +1,70 @@
+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
+```