PDP11 PeripheralsHbk 1972 - Trailing-Edge

TU 10 MAGTAPE UNIT
3.2.2 Operation
Reading and writing occurs when the tape is moving forward, but the control can
move the tape to new positions in forward or reverse. For writing on tape, 8-bit
data words are transferred from core memory to a data buffer in the controller.
The data buffer logic supplies the character to the tape transport write logic. For
reading, the sequence is reversed; and information is read from tape as 6-bit
characters (for 7 track tape; 8 bits for 9 track tape) which are sent to the data
buffer. When a complete 8-bit word has been assembled in the data buffer, a data
channel word transfer is initiated to transfer the data buffer word into core
memory.
The 7- and 9-track system use 1/2-inch mylar base tape which is coated on one
side with an iron oxide composition. The method of recording is non-return-tozero
(NRZ). A seven track tape includes six data channels and a lateral parity
channel. Density modes of 200, 556, and 800 bytes per inch are selectable. Nine-
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