diff --git a/main.tex b/main.tex
index 892b1d9..fd92be1 100644
--- a/main.tex
+++ b/main.tex
@@ -22,6 +22,34 @@
   \vspace{1em}
 \end{center}
 
+\noindent
+\begin{center}
+  \begin{tabular}{>{\ttfamily}cl}
+    \toprule
+    \multicolumn{2}{>{\sffamily\bfseries}c}{Register Usage} \\
+    \midrule
+    rax & Syscall number \\
+        & Return value \\
+    rdi & First argument \\
+    rsi & Second argument \\
+    rdx & Third argument \\
+    \bottomrule
+  \end{tabular}
+  \hspace{1em}
+  \begin{tabular}{l>{$}r<{$}}
+    \toprule
+    \multicolumn{2}{>{\sffamily\bfseries}c}{Common open(2) Flags} \\
+    \midrule
+    Read-only & 0_h \\
+    Write-only & 1_h \\
+    Read/write & 2_h \\
+    Create & 40_h \\
+    Truncate & 200_h \\
+    Append & 400_h \\
+    \bottomrule
+  \end{tabular}
+\end{center}
+
 \section{File I/O}
 
 \begin{tabularx}{\textwidth}{p{4em}p{2em}>{\ttfamily}cX}