I am not sure what I am doing wrong, but the arrow head on the link from the bottom left box to the upper right box does not show up. I want it to be the same as the arrow heads on the other edges. Thanks.
\documentclass{scrartcl}
\usepackage{tikz}
\usetikzlibrary{shapes,positioning,arrows}
\tikzstyle{every entity} = []
\tikzstyle{every link} = []
\tikzstyle{smentity} = [rectangle, draw, black,
minimum width=4em, minimum height=2em,
every entity]
\tikzstyle{link} = [>=triangle 60, draw, thick, every link]
\begin{document}
\begin{tikzpicture}[node distance=1.5cm, every edge/.style={link}]
\node[smentity] (3) {0001 1000};
\node[smentity] (4) [right= of 3] {1000 0001} edge[<-,dashed] node[above] {\small{01000}} (3);
\node[smentity] (5) [below= of 3] {1000 0000};
\node[smentity] (6) [right= of 5] {1000 0100} edge[->,dashed] (4);
\draw[>=triangle 60,dashed,thick] (5.east) -- ++(0.8,0) node[below,xshift=-0.4cm]{\small{01000}} -| ++(0,2) -- (4.196);
\end{tikzpicture}
\end{document}

->. Instead you can directly put[-triangle 60,dashed,thick]– percusse Sep 30 '12 at 12:26