parallel through metal levers. Configuration of user-selectable options was done with mechanical clips that depressed or released various levers. Sensing of punched holes by the paper tape reader was done by using metal pins which mechanically probed for their presence or absence. Earlier Teletype machine designs, such as the Model 28 ASR, had allowed the user to operate the keyboard to punch tape while independently transmitting a previously punched tape, or to punch a tape while printing something else. Independent use of the paper tape punch and reader was not possible with the Model 33 ASR. The tape punch required oiled paper tape to keep its mechanism lubricated. There was a transparent, removable chad receptacle beneath the tape punch, which required periodic emptying. The entire Model 33 ASR mechanism required periodic application of grease and oil in approximately 500 locations. Everything was mechanically powered by a single electric motor, located at the rear of the mechanism. The motor ran continuously as long as power was on, generating a familiar humming and slight rattle from its vibration. The noise level increased considerably whenever the printing or paper tape mechanisms were operating. Similar noises became iconic for the sounds of an active newswire or computer terminal. There was a mechanical bell, activated by code 07 (Control-G, also known as BEL), to draw special attention when needed. The Model 33 keyboard used the seven-bit ASCII code, also known as CCITT International Telegraphic Alphabet No. 5, with one (even) parity bit and two stop bits, with a symbol rate of 110 baud, but it only supported an upper-case subset of that code; it did not support lower-case letters or the , , , , and characters. The paper tape reader and punch could handle 8-bit data, allowing the devices to be efficiently used to download or upload binary data for computers. The mechanism was usually geared to run at a maximum ten characters per second speed, or 100 words per minute (wpm), but other slower speeds were available: 60 wpm, 66 wpm, 68.2 wpm, and 75 wpm. There were also many typefont options. The Teletype Parts Bulletin listed 69 available Model 33 type element options. The type element was cylindrical, with characters arranged in four tiers, 16 characters per tier, and thus was capable of printing 64 characters. The character to be printed was selected by rotating the type element clockwise or anticlockwise and