Transaction Printing is quickly explained by an unwanted example, printing bills. A digital printing system is attached to a computer database and many similar pages, called forms, are printed; each with a different person's data filling the form such as your monthly telephone or cable bill. Transaction print jobs are different from 'publishing' print jobs in that the print controller does not know when the job will end when it starts. It may be printing a hundred, a thousand or a few million impressions before the 'job' ends. Many digital printing system's controllers are designed to ingest the entire job, arrange its resources according to the size of the job and then begin printing the job last page first so that what is produced is a 'book' with the user seeing the first page first. This 'publishing' model obviously doesn't work for 'transaction' printing and a controller using a different internal model for jobs must be used.