Abstract: A peripheral unit is able to receive a plurality of control languages, check for an occurrence of a control language job boundary, and to function in response to each control language. For PCL the steps that determine when to check for occurrence of a control language job boundary are: identify the next command from the input data stream; determine if the identified command is not a PCL control character or calls for a mark to be made on the page, and if the page has not been previously marked. If the above criteria is met, the command and following data are examined to determine if a job boundary has occurred. Thus at the commencement of every formatted PCL page of data, a decision is made whether a job boundary has occurred. For PostScript the steps are: prescan the data stream. If a next command is an end-of-job marker then exit PostScript and return to identify the language of the input data.