RCA 301, Programmer'S Reference Manual

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ORGANIZATION OF DATA
Definitions
Bit: A bit is a single binary digit, having a value of either zero or one.
Character: An RCA 301 character consists of six information bits and one parity bit combined to represent a
decimal digit, a letter of the alphabet, a punctuation or other special mark, or a control symbol.
Item: An item consists of such characters as are necessary to specify a particular unit of information (a numerical
quantity, an alphabetic name, a street address, a stock number, etc.). In many cases an item is preceded by a symbol
to define the beginning of each item.
Record: A record consists of one or more related items with the amount of information in a record being
completely variable.
Line: A line is composed of the characters that are to be printed on a single line on the On-Line Printer. One
model of the On-Line Printer permits 120 characters to be printed per line. A second model permits 160 characters
to be printed per line.
Block: On magnetic and paper tape a block is a group of at least three characters preceded and followed by a
blank space called an "interlock gap."
On the Data Record File record a block is defined as the information contained in one cell. From one through
900 characters of information may be recorded in a cell. If the block is composed of less than 900 characters, the
last character will be an EB symbol (End of Block). If the block is composed of 900 characters, the last character
may or may not be an EB symbol. On the Data Disc File disc a block is defined as the information contained in
1 to 10 sectors. Each sector contains 160 characters.
File: A file consists of any number of related information records and may consist of only a part of a Data
Record File record or Data Disc File disc, or several records or discs. On magnetic tape it may consist of several
tapes or any part of one tape.
Organization of Data on Paper Tape
In the RCA 301 system, characters are represented on paper tape by combinations of holes punched in rows
across the tape. A hole represents a zero bit in F1SM; the absence of a hole represents a one bit in HSM (see Figure 4).
Organization of Data on a Data Record File Record
Bits are recorded as magnetic spots on the face of each Data Record File record. Characters are written and
read out in bit-serial fashion, the seven bits of each character following each other in a spiral around the disc, as
shown in Figure 2.
Each side of the record is divided into two bands; each band is composed of ten cells; each cell has the capacity
to store 900 characters. The cells on a record are addressable individually or in groups of consecutive cells up to a
total of 10.
Organization of Data on a Data Disc File Disc
Bits are recorded as magnetic spots on the face of each Data Disc File disc. Characters are written and read
out in bit-serial fashion. The seven bits of each character following each other in concentric tracks around the
discs as shown in Figure 1.
Each side c
c
the disc is divided into nine zones of 128 tracks each. Each track contains 10 sectors of 160
characters each, The sectors are addressable individually or in groups of consecutive sectors up to a total of 10.
Organization of Data on Magnetic Tape
In an RCA 301 system, characters are recorded on magnetic tape as magnetic spots in rows across the tape.
On Hi-Data Tape, a magnetized spot represents a zero bit; the absence of a spot represents a one bit. All characters
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