Final answer:
The comma-delimited file used for updating with the Data Loader must include a column with the Force.com record ID values to uniquely identify each record.
Step-by-step explanation:
When performing an update with the Data Loader, the comma-delimited file must contain a column with the Force.com record ID values of the records. The Force.com record ID is necessary to uniquely identify each record that needs to be updated in Salesforce. Without this ID, the Data Loader would not know which records in the Salesforce database should be updated with the data from the file.