Difference between Cron and Crontab?

I am not able to understand the answer for this question: "What's the difference between cron and crontab." Are they both schedulers with one executing the files once and the other executing the files on a regular interval OR does cron schedule a job and crontab stores them in a table or file for execution?

http://en.wikipedia.org/wiki/Cron">**Wiki page** for Cron mentions :

> Cron is driven by a crontab (cron table) file, a configuration file > that specifies shell commands to run periodically on a given schedule.

But https://help.dreamhost.com/hc/en-us/articles/215088608-Crontab-overview">**wiki.dreamhost**</a> for crontab mentiones :

> The crontab command, found in Unix and Unix-like operating systems, is > used to schedule commands to be executed periodically. It reads a > series of commands from standard input and collects them into a file > known as a "crontab" which is later read and whose instructions are > carried out.

Specifically, When I schedule a job to be repeated : (Quoting from wiki)

1 0 * * *  printf > /var/log/apache/error_log

or executing a job only once

at -f myScripts/call_show_fn.sh 1:55 2014-10-14

Am I doing a cron function in both the commands which is pushed in crontab OR is the first one a crontab and the second a cron function?

cron is the general name for the service that runs scheduled actions. crond is the name of the daemon that runs in the background and reads crontab files. A crontab is a file containing jobs in the format

minute hour day-of-month month day-of-week	command

crontabs are normally stored by the system in /var/spool/<username>/crontab. These files are not meant to be edited directly. You can use the crontab command to invoke a text editor (what you have defined for the EDITOR env variable) to modify a crontab file.

There are various implementations of cron. Commonly there will be per-user crontab files (accessed with the command crontab -e) as well as system crontabs in /etc/cron.daily, /etc/cron.hourly, etc.

In your first example you are scheduling a job via a crontab. In your second example you're using the at command to queue a job for later execution.