Difference between Salesforce external objects and custom objects

Feature Custom Objects External Objects
Data is stored in your Salesforce org Yes No
Read Yes Yes
Write Yes Yes (limited)
Tabs, layouts Yes Yes
Visualforce Yes Yes
Field-level security Yes Yes
Sharing Yes No
REST and SOAP API Yes Yes
SOQL Yes Yes (limited)
Search and SOSL Yes Yes (pass-through)
Formula fields Yes Not Yet
Workflow, triggers Yes Not Yet
Reports and analytics Yes Not Yet
Chatter Yes Yes (no field tracking)