As technology continues to pervade the classroom (see "Stay Tuned for More Knowledge," Page 26), even the classic textbook is in danger of being relegated to the shelves of historical artifacts. By the year 2005, digital delivery of custom-printed books, textbooks and e-books will account for 17.5 percent of the publishing market and produce nearly $8 billion in revenue, according to Cambridge, Mass.-based Forrester Research. The content of a digital textbook is stored in a computer file that lives on the Internet or on a student\u2019s hard drive. To access the information, students and teachers download a reader application from the respective e-textbook company, which presents the content in a booklike format. As with traditional books, readers can then highlight passages, scribble notes in the margins and dog-ear pages. Students can also search the text by word or phrase. Some digital textbooks cost the same as their paper counterparts, while others cost from 30 percent to 50 percent less.One advantage of a digital textbook is that professors can comment on the material online to reinforce readings or set up discussion sections about particular readings by placing a URL next to the text in question. URLs can also link to websites, self-tests and other study tools. Student access to digital textbooks varies according to the textbook company. MetaText, a subsidiary of NetLibrary based in Boulder, Colo., is accessible only to Web-enabled computers. New York City-based WizeUp.com\u2019s texts are available through downloads, which can clog up both a school\u2019s network and space in a student\u2019s hard drive. Rovia, based in Boston, requires students to access the books online but recently began to allow students to check out chapters for offline use.