what is a main difference between rhel 6 and rhel 7 accourding to rhel exam
 

i am doing rhel 6 by myself and i almost completed more than 60% portion for rhel 6 exam now i came to know that redhat will not conduct any exam for rhel 6 should i take rhel 7 classes from institute. I have some useful material for rhel 6 downloaded from net. By what percentage this rhel 7 different from rhel 6 accourding to examination point of view.If it differs 30-35 percent then i will try myself first and if differ above 35% i will joint institite.
please help me to take decission early.

If you have questions about the Red Hat exams, you need to contact the Red Hat training center you're working with, or Red Hat directly. There is nothing we can really tell you.

The BIG difference is systemd, and that affects how the system is configured for service.

A quick google leads you to this page on Redhat's site and is creatively named as: Changes between Red Hat Enterprise Linux 6 and 7

as posted above
we will not do your homework

BUT
we will point you to things

google

SystemV VS SystemD

thanks TBOne, jpollard, john vv, jkirchner i install rhel 7 and i find similar with rhel 6 and for exam i need to upgrade some topics such as sysdemd ...

I'm really not sure what this post means.

I have extensive experience with RHEL/CentOS-6, and I've just recently started diving into 7. Beyond the standard CLI commands, nothing is the same. The DE is different, the graphical config utilities are different, the startup files are different, the method to start/stop/restart the services is different, the method to autostart the services is different.

The difference between RHEL6 and RHEL7 is comparable to the difference between RHEL6 and any other modern Linux distro, other than the package management system. In other words, it's practically a completely different distro.