best practice for crontabs

Hi, I have just figured out that there are 4 separate (types of) crontabs in debian /etc/crontab /etc/cron.d/... /etc/cron.daily, monthly, weekly /var/spool/crontabs/... but I'm none the wiser about why there are so many ways to do such a simple thing. Can anyone enlighten me as

system performance monitor

Hi, I am new to debian and I'm looking for some kind of performance monitor that gives an instantaneous readout of typical performance indicators like memory, cpu and network bandwidth. it should be terminal based if at all possible as the machine is hosted and doesn't have X installed. Along the