order byte. Operand fields may be located on any
byte boundary, and may have length up to 31 digits
and sign.Operands participating in an operation have
independent lengths.Packing of digits within a byte
(Figure 8) and of variable-length fields withinstor age results in efficient use of storage, in increased
arithmetic performance, and in an improved rate of
data transmission between storage and files.I Digit I Digit I Digit Digit I Digit I Digit I Digit I Sign I I Zone I Digit I Zone C-_- Digit I Zone I Digit I Sign I Digit I Figure 8. Packed and Zoned Decimal Number Formats
Decimal numbers may also appear in a zonedfor mat as a subset of the eight-bit alphameric character
set (Figure 8). This representation is required for
character-set sensitiveI/O devices. The zoned format
is not used in decimal arithmetic operations.Instruc tions are provided for packing and unpacking decimal
numbersso that they may be changed from the zoned
to the packed format and vice versa.
Floating-Point Arithmetic
Floating-point numbers occur in either of twofixed length formats -short or long. These formats differ
only in the length of the fractions (Figure 9).
Short Floating-Point NumberIS I Characteristic I Fraction
oI 7 8 31
Long Floating-Point Number _________ F_ra_c_ti_o_n ______ ______ o 1 78 63
Figure 9.Short and Long Floating-Point Number Formats Operands are either 32 or 64 bits long. The short
length, equivalent to seven decimal places ofpre cision, permits a maximum number of operands to be
placed in storage and gives the shortest execution
times. The long length, used when higher precision is
desired, gives up to 17 decimal places of precision,
thus eliminating most requirements fordouble-pre cision arithmetic.
The operand lengths, being powers of two, permit
maximum efficiency in the use of binary addressing
and in matching thephys,ical word sizes of storage.
Floating-point arithmetic is designed to allow easy
transition between the two formats.
The fraction of a floating-point number is expressed
in hexadecimal ( base 16) digits, each consisting of
four binary bits and having the values0-15. In the
short format, the fraction consists of six hexadecimal
digits occupying bits 8-31. In the long format the
fraction has 14 hexadecimal digits occupying bits 8-63.
The radix point of the fraction is assumed to beim mediately to the left of the high-order fraction digit.
To provide the proper magnitude for thefloating point number, the fraction is considered to be mul tiplied by a power of 16. The characteristic portion,
bits 1-7 of both formats, is used to indicate this power.
The characteristic is treated as an excess 64 number
with a range from -64 through +63, and permits
representation of decimal numbers with magnitudes
in the range of10-
78 to 10
75
• Bit position 0 in either format is the sign (S) of the
fraction. The fraction of negative numbers is carried
in true form.
Four 64-bit floating-point registers are provided.
Arithmetic operations are performed with oneoper and in a register and another either in a .register or
from storage. The result, developed in a register, is
generally of the same length as the operands. The
availability of several floating-point registerselimi nates much storing and loading of intermediate re sults. Logical Operations
Logical information is handled as fixed-length and
variable-length data. It is subject to such operations as
comparison, translation, editing, bit testing, and bit
setting.
When used as a fixed-length operand, logicalin formation can consist of either one, four, or eight
bytes and is processed in the general registers.
A large portion of logical information consists of
alphabetic or numeric character codes, calledalpha meric data, and is used for communication with char acter-set sensitive I/O devices. This information has
the variable-field-Iength format and can consist of up
to 256 bytes (Figure10). It is processed in storage,
left to right, an eight-bit byte at a time.
TheCPU can handle any eight-bit character set, al though certain restrictions are assumed in the decimal
arithmetic and editing operations. However, allchar acter-set sensitive I/O equipment will assume either
the extended binary-coded-decimal interchange code
System Structure 11
byte boundary, and may have length up to 31 digits
and sign.
independent lengths.
(Figure 8) and of variable-length fields within
arithmetic performance, and in an improved rate of
data transmission between storage and files.
Decimal numbers may also appear in a zoned
set (Figure 8). This representation is required for
character-set sensitive
is not used in decimal arithmetic operations.
numbers
to the packed format and vice versa.
Floating-Point Arithmetic
Floating-point numbers occur in either of two
only in the length of the fractions (Figure 9).
Short Floating-Point Number
o
Long Floating-Point Number
Figure 9.
length, equivalent to seven decimal places of
placed in storage and gives the shortest execution
times. The long length, used when higher precision is
desired, gives up to 17 decimal places of precision,
thus eliminating most requirements for
The operand lengths, being powers of two, permit
maximum efficiency in the use of binary addressing
and in matching the
Floating-point arithmetic is designed to allow easy
transition between the two formats.
The fraction of a floating-point number is expressed
in hexadecimal ( base 16) digits, each consisting of
four binary bits and having the values
short format, the fraction consists of six hexadecimal
digits occupying bits 8-31. In the long format the
fraction has 14 hexadecimal digits occupying bits 8-63.
The radix point of the fraction is assumed to be
To provide the proper magnitude for the
bits 1-7 of both formats, is used to indicate this power.
The characteristic is treated as an excess 64 number
with a range from -64 through +63, and permits
representation of decimal numbers with magnitudes
in the range of
78
75
•
fraction. The fraction of negative numbers is carried
in true form.
Four 64-bit floating-point registers are provided.
Arithmetic operations are performed with one
from storage. The result, developed in a register, is
generally of the same length as the operands. The
availability of several floating-point registers
Logical information is handled as fixed-length and
variable-length data. It is subject to such operations as
comparison, translation, editing, bit testing, and bit
setting.
When used as a fixed-length operand, logical
bytes and is processed in the general registers.
A large portion of logical information consists of
alphabetic or numeric character codes, called
the variable-field-Iength format and can consist of up
to 256 bytes (Figure
left to right, an eight-bit byte at a time.
The
arithmetic and editing operations. However, all
the extended binary-coded-decimal interchange code
System Structure 11