7 8 11 12 15
7 8 11 12 1516
7 8 11 12
struction stream in main storage, and operands lo
cated in the general or floating-point registers.
To permit the ready relocation of program seg
ments and to provide for the flexible specifications of
input, output, and working areas, all instructions re
ferring to main storage have been given the capacity
of employing a full address.
The address used to refer to main storage is gen
erated from the following three binary numbers:
Base Address (B) is a 24-bit number contained in a
general register specified by the program in the B
field of the instruction. The B field is included in
every address specification. The base address can be
used as a means of static relocation of programs and
data. In array-type calculations, it can specify the lo
cation of an array and, in record-type processing, it
can identify the record. The base address provides for
addressing the entire main storage. The base address
may also be used for indexing purposes.
Index (X) is a 24-bit number contained in a general
register specified by the program in the X field of the
instruction. It is included only in the address speci-
fied by the RX instruction format. The index can be
used to provide the address of an element within an
array. Thus, the
Displacement (D) is a 12-bit number contained in
the instruction format. It is included in every address
computation. The displacement provides for relative
addressing up to
base address. In array-type calculations the displace
ment can be used to specify one of many items as
sociated with an element. In the processing of records,
the displacement can be used to identify items within
In forming the address, the base address and index
are treated as unsigned 24-bit positive binary integers.
The displacement is similarly treated as a 12-bit posi
tive binary integer. The three are added as 24-bit
binary numbers, ignoring overflow.
dress includes a base, the sum is always 24 bits long.
The address bits are numbered 8-31 corresponding to
the numbering of the base address and index bits in
the general register.