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