Order of execution in Salesforce Professional edition

Hi kumar

Yes it differs, if the edition is Professional Edition. PE doesn't have Triggers.

UE- Unilimited Edition EE - Enterprise Edition

Old record loaded from database (or initialized for new inserts)
New record values overwrite old values
System Validation Rules (If inserting Opportunity Products, Custom Validation Rules will also fire in addition to System Validation Rules)
All Apex before triggers (EE / UE only)
Custom Validation Rules
Record saved to database (but not committed)
Record reloaded from database
All Apex after triggers (EE / UE only)
Assignment rules
Auto-response rules
Workflow rules
Processes
Escalation rules
Parent Rollup Summary Formula value updated (if present)
Database commit
Post-commit logic (sending email