GE 235 System Manual page 65

Tapes may be used a s on-line storage during a computer run.
Tapes may be used a s off-line storage to retain masses of information a s a file for subse-
quent related computer runs.
Magnetic tapes may be erased and used repeatedly.
Each cabinet contains two magnetic tape handlers.
Each handler holds two 10-1/2 inch diameter reels, one for feeding, and one for taking up
the tape.
Each reel holds up to 2,400 feet of standard 1/2-inch wide magnetic tape.
Data i s recorded in groups of words called blocks with short blanks in tape separating
blocks.
F O R M A T S
The Tape Handler i s capable of reading either backwards or forward in three formats: a Binary
Coded Decimal, Binary, and Special Binary. The programmer selects the format he desires for his
specific application. The tape has awidth sufficient for the recording of seven tracks, o r channels,
of data. Six bits of data a r e recorded across the tape; a parity bit i s recorded in the seventh track.
Parity, odd o r even, depends on the format being used. In the binary format, the lateral one-bits
will always be odd (known a s odd parity). In BCD, the parity i s even. This i s simply a safeguard
to prevent an inadvertent programming e r r o r that might a r i s e if reading a tape prepared in the
binary format with a Read Decimal type command.
Data i s written on tape in groups of words called blocks of fixed o r differing length. Inter-block
gaps physically separate magnetic tape blocks. This gap i s a 3/4-inch section of erased tape
allowed f o r starting and stopping tapes between blocks. An end-of-file block separates groups of
information, o r marks the end of information on a specific tape. It i s an erased section 3-3/4
inches long, followed by the code combination 0001111 and the parity character.
Binary Coded ~ e c i m a l Format
In the BCD format, in tape reading and writing operations, three 6-bit characters contained in the
GE-235 word a r e transferred to and from tape. Thus, in the BCD format, some character bit con-
figurations a r e altered so a s to make the GE-235 system compatible with other tape systems in use.
This alteration i s accomplished automatically.