Eu acho que sua pergunta é muito ampla para ser respondida completamente aqui, mas vou responder com uma lista truncada em termos de 'grandes' mudanças tomadas a partir do wiki do CentOS :
As with every first major Release most of the packages have changed and have been updated to more recent versions. It would exceed the scope of this document to list them all. Most notable changes are:
Kernel updated to 3.10.0 Support for Linux Containers Open VMware Tools and 3D graphics drivers out of the box OpenJDK-7 as default JDK In Place Upgrade from 6.5 to 7.0 (as already mentioned) LVM-snapshots with ext4 and XFS Switch to systemd, firewalld and GRUB2 XFS as default file system iSCSI and FCoE in kernel space Support for PTPv2 Support for 40G Ethernet Cards Supports installations in UEFI Secure Boot mode on compatible hardware
Para informações mais detalhadas sobre alterações, sugiro ler sobre Notas de versão do RHEL 7.0 .