--- manual/s_phys_pkgs/rw.tex	2004/01/28 18:12:29	1.1
+++ manual/s_phys_pkgs/rw.tex	2004/01/29 14:43:14	1.3
@@ -1,5 +1,26 @@
 \section{Basic binary I/O utilities}
-\label{sec:rw}
+\label{sec:pkg:rw}
+The {\tt rw} package provides a very rudimentary binary I/O capability
+for quickly writing {\it single record} direct-access Fortran binary files. 
+It is primarily used for writing diagnostic output.
+
+\subsection{Introduction}
+Package {\tt rw} is an interface to the more general {\tt mdsio} package.
+The {\tt rw} package can be used to write or read direct-access Fortran 
+binary files for two-dimensional XY and three-dimensional XYZ arrays. 
+The arrays are assumed to have been decalred according to the standard
+MITgcm two-dimensional or the-dimensional floating poit array type e.g
+\begin{verbatim}
+C     Example of declaring a standard two dimensional "long" floating
+C     point type array (the _RL macro is usually mapped to 64-bit 
+C     floats in most configurations)
+      _RL anArray(1-OLx:sNx+OLx,1-OLy:sNy+OLy,nSx,nSy)
+\end{verbatim}
+Each call to an {\tt rw} read or write routine will read (or write) to the 
+first record of a file. To write files with multiple records use the 
+package {\tt mdsio} (see section) or the package {\tt mnc} (see section {sec:pkg:mnc}) 
+which produces netCDF \cite{rew:97} based output.
+
 \subsection{Key subroutines, parameters and files}
 \label{sec:pkg:rw:implementation_synopsis}
 \subsection{Package Reference}