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+lib
+===
+
+This directory contains numerous, small functions typically associated with
+what you would expect to find in a standard C library.  The sub-directories
+in this directory contain standard interface that can be executed by user-
+mode programs.
+
+Normally, NuttX is built with no protection and all threads running in kerne-
+mode.  In that model, there is no real architectural distinction between
+what is a kernel-mode program and what is a user-mode program; the system is
+more like on multi-threaded program that all runs in kernel-mode.
+
+But if the CONFIG_NUTTX_KERNEL option is selected, NuttX will be built into
+distinct user-mode and kernel-mode sections.  In that case, most of the
+code in the nuttx/ directory will run in kernel-mode with with exceptions
+of (1) the user-mode "proxies" found in syscall/proxies, and (2) the
+standard C library functions found in this directory.  In this build model,
+it is critical to separate the user-mode OS interfaces in this way.
+
+Sub-Directories
+===============
+
+The files in the lib/ directory are organized (mostly) according which file
+in the include/ directory provides the prototype for library functions.  So
+we have:
+
+  libgen    - libgen.h
+  math      - math.h and fixedmath.h
+  mqueue    - pthread.h
+  net       - Various network-related header files: netinet/ether.h, arpa/inet.h
+  pthread   - pthread.h
+  queue     - queue.h
+  sched     - sched.h
+  semaphore - semaphore.h
+  stdio     - stdio.h
+  stdlib    - stdlib.h
+  string    - string.h
+  time      - time.h
+  unistd    - unistd.h
+
+There is also a misc/ subdirectory that contains various internal functions
+and interfaces from header files that are too few to warrant their own sub-
+directory:
+
+ misc       - Nonstandard "glue" logic, debug.h, crc32.h, dirent.h
+