\clearpage
\section{Disk Geometry}
\begin{frame}
   {Disk Geometry}

   \begin{itemize}
      \item \textbf{Rotational} disks are composed of one or
      more platters and each platter is read by one or
      more heads
      \item Heads read a circular track off a platter as the
      disk spins
      \item Circular tracks are divided into data blocks
      called sectors
      \item Originally, sectors were 512 bytes of data; now usually 4096 bytes
      \item A cylinder is a group which consists of the same
      track on all platters
      \item For \textbf{SSD}s these geometry concepts make no
      sense
   \end{itemize}
   \begin{lfbox}
      \begin{cmd}
$ sudo fdisk -l /dev/sdc |grep -i sector
   \end{cmd}
      \begin{response}
Disk /dev/sdc: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
   \end{response}
   \end{lfbox}
\end{frame}

\cprotect\note{

   The physical structural image has become less and less
   relevant as internal electronics on the drive actually
   obscure much of it.  Furthermore, \textbf{SSD}s have no
   moving parts or anything like the above ingredients.

   We can see the geometry with \textbf{fdisk}:

   \begin{figure}[H]
      \includegraphics[width=5.5in]{IMAGES/fdisk-pic}
      \caption{Using fdisk}
   \end{figure}

   Note the use of the \texttt{-l} option which simply lists
   the partition table without entering interactive mode.


   Historically disks were manufactured with sectors of 512
   bytes; 4 KB is now most common by far; larger sector sizes
   can lead to faster transfer speeds.  \textbf{Linux} still
   uses a \textbf{logical} sector size of 512 bytes for
   backward compatibility, but this is simply for pretend in
   software.
}

