IBM 7090 - Computer Operations; Storage Word Designation; The 7090 Word; Numeric Quantity (Data) Word

2. 0.00 COMPUTER OPERATIONS
A more detailed study of 7090 operations requires additional information about the sys-
tem. This section of the manual deals with the designation of each word location in
storage, the 36-position 7090 binary word, and the fundamental components of system
logic. Again, these will be applied to the problem, A+B = C, print C. In this descrip-
tion of the problem, the importance of the central processing unit (CPU) becomes more
apparent.
2.1. 00 STORAGE WORD DESIGNATION
The storage unit in the 7090 system contains 32,768 locations. Each of these word
locations is made up of 36 binary positions. Ordinarily, all 36 positions of anyone
word are moved to or from storage at one time. This is known as parallel data trans-
mission and allows the moving of a large numeric factor each time that storage reads
in or out.
Think of storage as a large double square of pigeon-holes as shown in Figure 2.1-1.
Each pigeon-hole has the capacity of a full 36-bit word. When a word is to be stored in
or taken from any location, this location must be designated. Obviously, there must be
32,768 of these designations, or addresses, one for each location. Because all opera-
tions in the 7090 system are done in binary notation, there are 15 binary positions used
for addressing storage locations. Only 15 are required because storage addresses are
expressed in octal numbers ranging from 00000 to 77777, rather than from 00001 to
100000. An address of all zeros designates the first word location in storage. Every
storage operation, whether directed by the CPU or a data channel, must be addressed.
2.2.00 THE 7090 WORD
A 7090 word may be a numeric quantity, a CPU instruction, or a data channel com-
mand. In all cases, the word is a full 36 positions. The logic format of a word differs
according to its use.
2.2.01 Numeric Quantity (Data) Word
Numbers, usually referred to as data, normally appear in true form in 35 of the 36
binary positions in the 7090 word. The remaining position is the algebraic sign of the
number (Figure 2.2-1). A binary bit, one, in the sign position is a negative sign. No
binary bit, zero, in the sign position of the word is a positive sign. The sign position
and the 35 numeric magnitude positions make up the format of the data word.
2.2.02 CPU Instruction Word
The CPU instruction word (Figure 2.2-2) has a different logic format. The CPU
instruction word gains its distinctive format because it is called for by CPU at a time
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