What is the difference between an incremental backup and a differential backup?

An Incremental backup backs up only the selected files that have their archive bit set to ON, setting them back to OFF.
a backup of all files that are new or changed since the last backup whether it was a full or an incremental.
The advantage of an Incremental is that it takes the least amount of time and media of all the backup methods.
In the case of restoring with Incremental backups, all the Incremental backups since the last full backup plus the last full backup would be necessary.




A Differential backup backs up only the selected files that have their archive bit set to ON but does not set the archive bit back to OFF.
A Differential backup will back up all selected files that are new and changed since the last full backup.
at restore time; you'll need only the last full backup and the last differential to get a complete restore

Reference:
http://wiki.answers.com/Q/What_is_the_difference_between_an_incremental_backup_and_a_differential_backup

• Continuous data protection (CDP), also called continuous backup or real-time backup, refers to backup of computer data by automatically saving a copy of every change made to that data, essentially capturing every version of the data that the user saves. In its true form it allows the user or administrator to restore data to any point in time

https://en.wikipedia.org/wiki/Continuous_Data_Protection

Simply stated, continuous data protection (CDP), also called continuous backup, is a storage system that backs up data whenever any change is made in it. In effect, CDP creates an electronic journal of complete storage snapshots, one for every instant in time that data modification occurs.

Why continuous data protection?
IT complexity: Continuous data protection helps ensure continuous availability of the varied, cross-platform environments.
Administrative capability:
Cost factor:Continuous data protection may prove to be a cheaper solution than traditional backup and recovery solutions. Software-based continuous data protection solutions today are easy to deploy and manage,
Data growth:  Remote users in geographically dispersed locations have access to email, core systems and other mission-critical applications. In such cases, continuous data protection makes perfect sense for enterprises with locations in multiple geographies.
Criticality of data:Continuous data protection technologies enable seamless backup and restore at the backend without affecting end users. Many continuous data protection solutions can recover data from any point in time within less than a minute.

Most of the challenges with continuous data protection emanate from the environment being targeted. A true continuous data protection solution will support real-time protection rather than scheduled snapshots. The change rate of the data sets that are being protected could pose challenges to the continuous data protection solution.
https://www.computerweekly.com/tip/Continuous-data-protection-Do-you-need-it