Bootchart is a tool that collects data from the PC at boot time, basically it shows a graph where you can see what was happening with CPU and Disk during the boot process of the PC.
It is more a tool to find where to optimize the GNU / Linux operating system boot process, as it shows when the disk or the CPU is idle, and thus wasting time, that can be gained in order to have a faster boot.
It also shows the process that run in that time and the resources them use.
From its homepage, we get this info about bootchart
“Bootchart is a tool for performance analysis and visualization of the GNU/Linux boot process. Resource utilization and process information are collected during the boot process and are later rendered in a PNG, SVG or EPS encoded chart.”
You can install it on Debian and Ubuntu and its derivatives
sudo aptitude install bootchart
Then after the next boot your will find graphs in the /var/log/bootchart directory like this one