in the first RFC, . The Model 35 was widely used as terminals for the minicomputers and IMPs to send and receive text messages over the very early ARPANET, which later evolved into the Internet. The Model 38 (ASR-38) was constructed similar to and had all the typing capabilities of a Model 33 ASR, plus additional features. A two-color inked ribbon and additional ASCII control codes allowed automatic switching between red and black output while printing. An extended keyboard and type element supported upper- and lower-case printing with some additional special characters. A wider pin-feed platen and typing mechanism allowed printing 132 columns on fan-fold paper, making its output similar to the 132-column page size of the then industry-standard IBM 1403 model printers. More-expensive Teletype systems had paper tape readers that used light sensors to detect the presence or absence of punched holes in the tape. These could work at much higher speeds (hundreds of characters per second). More sophisticated punches were also available that could run at somewhat higher speeds; Teletype's DRPE punch could operate at speeds up to 240 characters per second. Historical impact ASCII was first used commercially during 1963 as a seven-bit teleprinter code for American Telephone & Telegraph's Teletypewriter eXchange TWX network using Teletype Model 33 teleprinters. The upper-case-only limitation of the widely-used Teletype Model 33 constrained many early computer languages and systems to communicate in ALL CAPS, establishing an association of this text stylization with early computing technology in general. The Teletype Model 33 series was influential in the development and interpretation of ASCII code characters. In particular, the Teletype Model 33 machine assignments for codes 17 (Control-Q, DC1, also known as XON) and 19 (Control-S, DC3, also known as XOFF) became de facto standards. The programming language BASIC was designed to be written and edited on a low-speed Teletype Model 33. The slow speed of the Teletype Model 33 influenced the user interface of minicomputer operating systems, including UNIX. A Teletype Model 33 provided Bill Gates' first computing experience. In 1965, Stanford University psychology professors Patrick Suppes and Richard C. Atkinson, in the pilot program for computer assisted instruction, experimented with using computers to provide arithmetic and spelling drills via Teletypes and acoustic couplers to elementary school students in the Palo Alto Unified School District in California and elsewhere. In 1971, Ray Tomlinson chose the "@" symbol on his Teletype Model 33 ASR