Update vs Systemupdate vs UpdateOverwriteVersion

When creating event receivers or workflows it might be interesting to look at the differences between the following SPListItem methods. The differences might be subtle but it can make a huge difference when you have extra event receivers or workflows attached to your SharePoint list or items.

Update()

• Updates the item in the database.
• Updates the “Modified” and “Modified by” values.
• Creates a new version

Systemupdate()

• Updates the item in the database.
• No changes in the “Modified” and “Modified By” fields.
• No new version.
• Triggers the item events.

Systemupdate(true)

• Same as Systemupdate() and increments the item version.
• Using SystemUpdate(false) is exactly the same as SystemUpdate()

UpdateOverwriteVersion()

• Updates the item but does not create a new version.
• Updates the “Modified” and “Modified by” values.

Note that :
You can also disable the triggering of events by using “this.EventFiringEnabled = false;”. Do your update and enable the events again with “this.EventFiringEnabled = true;”