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File No. 1401-00
Form A24-1401-1
Systems Reference Library
IBM 1401 System Summary
This reference publication contains brief descriptions
of the machine features, components, configurations,
and special features. Also included is a section on pro-
grams and programming systems.
Publications providing detailed information on sub-
jects discussed in this summary are listed in IB~I 1401
and 1460 Bibliography, Form A24-1495.
Major Revision (September 1964)
This publication, Form A24-1401-1, is a major revision of and
obsoletes Form A24-1401-0. Significant changes have been made
throughout the publication.
Reprinted April 1966
Copies of this and other IBM publications can be obtained through IBM Branch Offices.
Address comments concerning the content of this publication to IBM Product Publications, Endicott, New York 13764.
Contents
IBM 1401 System Summary . ........... . 5
System Concepts . ................ . 6
Card-Oriented System .... . ......... . 11
Physical Features. . . . . . . . . . . . . . .......................... 11
Interleaving. . . . . . . . .. . .................................... . 14
Data Flow.... ... ... ... ... .. . ... ... .. . ................... . 14
Checking ................................................... . 15
Word Mark.. ... ... ... ... ... ... .. . ... ... ... . ........... . 15
Stored-Program Instructions. . . . .................. . 15
Operation Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18
Editing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ............ . 18
IBM 1401 Console ............................................ . 19
IBM 1406 Storage Unit. . . ........................... . 20
Magnetic-Tape-Oriented System . ........................... . 22
Data Flow .................................................. . 22
Magnetic Tape. 22
Disk-Storage-Oriented System . .. 26
Data Flow ................ . 26
IBM 1311 Disk Storage .. 26
IBM 1405 Disk Storage. 28
IBM 1407 Console Inquiry Station. 29
Special Features . . 30
IBM 1401 Processing Unit. 30
IBM 1402 Card Read-Punch .. 32
IBM 1403 and 1404 Printers. . . ..... 33
IBM 1405 Disk Storage . . . . . . . . . . . . . . . . . . . . . . . .. 33
IBM 1311 Disk Storage Drive. 33
Other Input/Output Units for the IBM 1401 System . ......... . 35
IBM 1009 Data Transmission Unit. . . . . . . .. 35
IBM 7710 Data Communication Unit .... 35
IBM 7740 Communication Control System 36
IBM 7770 Audio Response Unit .............. . 36
IBM 1026 Transmission Control Unit .. 36
IBM 1011 Paper Tape Reader .. . 37
IBM 1012 Tape Punch ........ . 37
IBM 1231 Optical Mark Page Reader .... 37
IBM 1285 Optical Reader . . . . . ......... 38
IBM 1412 and 1419 Magnetic Character Readers ................... . 38
IBM 1418 Optical Character Reader. . . . . . . . . . . . . .......... . 38
IBM 1428 Alphameric Optical Reader ............................ . 39
IBM 1404 Printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ............. . 39
IBM 1445 Printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 40
IBM 7340 Hypertape Drive Model 2 .. 40
IBM 1401 Programs and Programming Systems . .. . 42
Index ...................................................... . 56
Figure 1. IBM 1401 Data Processing System
IBM 1401 System Summary
The IBM 1401 Data Processing System is designed to The IBM 1401 system can also accommodate input
provide the transition from punched-card data process- from and output to various other IBM units: Tele-proc-
ing equipment to the data processing system and to ac- essing or data communications units, magnetic-ink and
commodate subsequent business growth through the optical-character-sensing units, and paper-tape units.
various IBM 1401 system configurations. A data proc- The IBM 1401 Processing Unit operates under con-
essing system consists of functional units to provide: trol of a stored program. The processing unit receives
data input, data processing, and data output. input data from an input unit, processes the data, and
provides output to an output unit. Machine instruc-
The IBM 1401 system implements punched-card input
tions of the stored program direct the processing of
and output, at speeds much faster than punched-card
data. The processing unit and the various input and
data processing equipment. This permits fast and eco-
output units can be equipped with special features to
nomical data processing in areas where punched-card
provide further advantages in system operation and
data processing is desirable but not fully efficient using programming.
punched-card data processing equipment.
IBM also provides programs and programming sys-
Magnetic tape and magnetic disk can be used as tems to relieve IBM 1401 users of much detailed pro-
sources of input data for processing and as devices for gramming effort. Among these are symbolic-language
storage of output data. Each has its area of use, but systems, report-program generating systems, disk file-
both provide storage for large volumes of data for organization programs, sorting and merging programs,
processing. utility programs, and input/output control systems.
5
System Concepts
The IBM 1401 can be considered in three major con-
figurations: the card-, tape-, and disk-storage-oriented
systems.
Card system configurations are planned for proce-
dures involving large volumes of card documents as
source data and output, with particular advantage to
applications requiring re-entry data.
Tape system configurations accomplish data proc-
essing through the use of magnetic tape. This has the
advantages of compact record handling and storage
medium for high-speed data processing systems.
Disk-storage system configurations, through mag-
netic-disk storage, permit in-line data processing and
increased storage capacity, in addition to all the ad-
vantages of a 1401 system.
The Stored Program
The main characteristic of data processing systems is
self-controlled performance of procedures, carried to
various degrees. Any such self-controlled performance
simply includes a series of actions or movements, each
depending on another and requiring no operator inter-
vention in the completion of the series. The series can Test Record
Turn Off
be very short, or very long. The series can be com- File for More
Machine
Records
pletely sequential, or the next action to be taken can be
determined by the last action completed.
An automatic record player is a good example bf a Figure 2. Block Diagram of a Program
series of actions, each one depending on the one imme-
diately preceding it. When records are loaded on the A data processing system is a group of various inter-
spindle and the record player is turned on, a record connected mechanical and electronic components. A
drops to the turntable; the playing arm positions itself system of this kind must be able to handle and com-
at the starting. position of the record; the record is plete such a program. The concept of stored program-
played; the arm retuTns to a neutral position; the next ming provides this flexibility and efficiency.
record in sequence drops into place; the playing arm In punched-card data processing, the wires in the
returns to the starting position on the new record; the control panel actually comprise the program of instruc-
record is played; and so on, until all the records have tions. The requirements of the procedure are studied
been played once, without any need for intervention or carefully, and then the proper wires are placed' in the
assistance by anyone. This series of actions is called a control panel. The entire program can be changed by
program (Figure 2). removing one control panel and replacing it with an-
In data processing systems, the program is more com- other for a different procedure. The factors limiting
plex. It controls the entire flow of data in and out of the extent to which punched-card data processing
various processing units. If, for instance, original data equipment can handle the program are the number of
is punched into cards, the program controls the read- program steps that can be provided within the physical
ing of this data, its transport to various processing areas confines of the control panel, and the number of con-
for addition, subtraction, multiplication, division, mod- trol panels that can be conveniently utilized.
ification, classification, recording, and any other kind of Stored-program data processing systems use a simi-
action to which data can be subjected. lar, but much more flexible, concept. All the instruc-
6 IBM 1401 System Summary
tions needed to complete a procedure are written in location of core storage addressable. Thus, a program
the form of program steps. These program steps are step can designate the exact cores needed for that step.
made available to the machine by various methods, the Each location of core storage consists of a number
most common of which is punched cards. The data of planes or levels of magnetic cores. Various combina-
processing system stores these program steps in a stor- tions of bits designate digits, letters, and special char-
age medium. acters (Figure 4). Notice that the planes are stacked,
Thus, when a procedure is to begin, the program is and the cores representing a single character (in this
loaded into the system (Figure 3), and the entire proce- case the letter A) are all at the intersection of the same
dure can be performed from beginning to end. The two wires in each plane.
IBM 1401 Data Processing System makes use of four The physical make-up of each core-storage location
kinds of storage: magnetic-core storage, magnetic-tape and its associated circuitry make it possible for the IBM
storage, magnetic-disk storage, and the already familiar 1401 to modify instructions and process data directly in
punched-card storage. the storage area. (This is called add-to-storage logic.)
The design, construction, and circuitry make the
Magnetic-Core Storage core-storage unit in the 1401 compact but extremely
All configurations of the IBM 1401 Data Processing powerful.
System use magnetic-core storage for storing instruc-
Magnetic-Tape Storage
tions and data.
Magnetic tape is made of plastic material, coated with
The magnetic-core storage unit is composed of a
a metallic oxide. It has the property of being easily
number of tiny rings made of magnetic material. Sev-
magnetized in tiny spots, so that patterns of these mag-
eral electric wires pass through each of these rings,
netized spots are codes for digits, alphabetic characters,
and each ring is magnetized.
and special characters.
Every magnetic field has polarity. This can be dem-
onstrated by the common phenomenon of two horse- location of letter "A"
shoe-shaped magnets, which attract each other firmly
when turned one way, and repel each other just as
strongly when turned the other way. Similarly, each
magnetic core possesses a magnetic field. The polarity
of this field is determined by whether a bit or a no-bit
of information is stored. A core magnetized in one di-
rection contains a bit of information. When the polarity
is reversed, the core contains a no-bit of information.
These two conditions are represented schematically by
bit values of 1 (representing a bit) and 0 (representing
a no-bit). All data in core storage is instantly available,
and in the IBM 1401, the core-storage units have been
specifically designed for high utility by making each
Storage
Stored Program
Figure 3. Stored Program Figure 4. The Letter A Represented in Magnetic-Core Storage
7
Data can be read from a variety of sources and put In addition to providing increased storage capacity,
on the tape. The magnetic spots representing the infor- magnetic-disk files permit processing data on a random
mation stored on the tape remain until they are either basis. Because any record on any track is addressable,
erased or written over. the IBM 1401 Processing Unit has access to any record
Because magnetic data can be kept permanently, in the disk-storage unit. This random accessibility is the
magnetic tape is an ideal storage medium for a large key to the in-line approach to data processing. Trans-
volume of information. The reels of tape (Figure 5) are actions can be entered as they occur-regardless of se-
removable from the system, and can be filed. They can quence. The 1401 can process other data within core
also be transported and used in other systems. storage while the access mechanism searches for a
Data stored on the magnetic tape is read sequen- record.
tially. The data processing system can search the tape
Language
to find the data to be used. Storing program steps on
In the punched-card area of data processing, the lan-
magnetic tape is a common method of collecting a
guage of the machine is the holes in the card. As data
library or file of programs.
processing needs increase, the basic card-language re-
Another great advantage of magnetic-tape storage is mains the hole in the card. But in the transition from
that a reel of tape produced as output of a procedure
punched-card data processing systems to data process-
can be removed from the data processing system. With ing systems, another faster, more flexible machine-lan-
this tape, reports can be written with an independent guage emerges.
unit, while the data processing system proceeds with
the next program. Just as each digit, letter, or special character is
coded into the card as a punched hole or a combina-
tion of holes, it is coded into magnetic storage as pat-
Magnetic-Disk Storage
terns of magnetized spots.
Magnetic disks are thin metal disks that are coated on
Obviously, many different code patterns can be set
both sides with a ferrous oxide recording material.
up. The internal code used in the IBM 1401 Data Proc-
These disks are mounted on a vertical shaft, and are
essing System is called Binary Coded Decimal. All data
separated from one another. As the shaft revolves, it
and instructions are translated into this code as they
spins the disks at a constant speed.
are stored. No matter how information is introduced
Information is recorded on disks in the form of mag- into the system, the binary-coded-decimal representa-
netized spots located in concentric tracks on each re- tion is used in all data flow and processing from that
cording surface. point on, until it is translated into printed output when
The magnetic disk can be used repeatedly. Each reports and documents are written or converted to card
time new information is stored on a track, it erases the code for punching. Converting input data to the 1401
data formerly stored there. Records can be read from internal code, and subsequently reconverting, is com-
disks as often as desired until they are written over or pletelyautomatic.
erased.
Processing
The manipulation that data undergoes in order to
achieve desired results is called processing. The part of
the 1401 system that houses these operations is called
the processing unit.
Processing can be divided into three general ca te-
gories: logic, arithmetic, and editing.
Logic
The logic function of any kind of data processing sys-
tem is not only its ability to execute program steps, but
also its ability to evaluate conditions and select alterna-
tive program steps on the basis of those conditions.
In punched-card data processing equipment, an ex-
ample of this logic is selector-controlled operations
based on an X or No-X, or based on a positive or nega-
tive value, or perhaps based on a comparison of control
Figure 5. Reel of Magnetic Tape numbers in a given card field.
8 IBM 1401 System Summary
Similarly, the logic functions of the 1401 system
make decisions and vary program operations based on
comparisons, or positive or negative values.
Arithmetic
The 1401 processing unit has the capacity to perform
add, subtract, multiply, and divide operations. Multi-
plication and division can be accomplished in any 1401
system by programmed subroutines. When the extent
of the calculations might otherwise limit the operation,
a direct multiply-divide feature is available.
Editing
As the term implies, editing adds significance to output
data by punctuating and inserting special characters
and symbols. The IBM 1401 has a unique ability to per-
form this function, automatically, with simple program
instructions.
Checking
Advanced circuit design with extremely reliable com-
ponents is built into the 1401 system to provide assur-
ance of accurate results. Self-checking within the ma-
chine is separated into three categories: parity, validity,
and hole count.
Solid-State Circuitry
Transistorized components (Figure 6) are another sig-
nificant design characteristic of the IBM 1401. In ad- Figure 6. Transistor Cards
dition to providing a lower cost system, the use of
transistors increases reliability, while decreasing main- Advanced Design
tenance requirements. Other advantages are carefully Advanced systems design of the IBM 1401 permits using
controlled: the machine as a complete, independent accounting
space requirements system. It can also perform low-cost, direct input and
heat dissipation output, and auxiliary tape operations for large-scale
power requirements. data processing systems.
The physical arrangement of the system components The entire system is operated by the stored program.
offers a less tangible, but equally important, benefit in Timesaving features, such as the powerful editing
greater operating efficiency, because the components function and the elimination of control panels, provide
requiring operator attention can be situated for accessi- increased flexibility for application development. The
bility and convenience. The controls and arithmetic capacity to use magnetic-tape data means economy in
components are consolidated into a single set of modu- recording, transporting, and storing large volumes of
lar cabinets. information in compact form; and the availability of
magnetic-disk storage permits in-line processing in ad-
Thus far, only the most obvious advantages offered
dition to providing increased storage capacity.
by the 1401 have been given. As the system components
and features are described in greater detail, further
advantages become evident. Power and economy of IBM 1401 Used with Other IBM Systems
the 1401 are not derived from any single characteristic
On-Line Operation
or component, but from the many considerations that
led to the design of a balanced system in which every The IBM 1401 Data Processing System can be attached
component can operate at its optimum rate. to either the IBM 7040 or the 7044 Data Processing Sys-
9
tern. This permits most of the components and features systems. One of these 1401 programs accepts IBM 1440
of the 1401 system to be used on-line with the larger source programs as input, producing an assembled ob-
system. ject program to be run on the IBM 1440. The other 1401
program accepts as input, source programs written for
Off-Line Operation
the IBM 7750 Programmed Transmission Control (a
component of certain IBM Tele-processing systems). It
The IBM 1401 has additional flexibility when it is used produces as output IBM 7750 object programs. Thus, the
with tape-oriented configurations of large-scale, gen- IBM 1401 Data Processing System can assist users in
eral-purpose IBM data processing systems. For exam- programming IBM 1440 systems and certain IBM Tele-
ple, the 1401 can produce, edit, sort, print, punch, and processing systems.
further manipulate tape data used by the IBM 7070 and
7080. This allows more time for the operations that are
IBM Scientific Data Processing Systems
more efficient and practical for each system.
The column-binary feature enables the 1401 to process
card and tape data recorded in binary form. This ability
Program Assembly for Other Systems
makes the 1401 especially useful as an auxiliary system
IBM provides two 1401 programs that assemble users' for the IBM 704, IBM 709, and IBM 7090 Data Processing
source programs written for other IBM data processing Systems.
10 IBM 1401 System Summary
Card-Oriented System
The IBM 1401 card-oriented system is completely tran- IBM 1401 Processing Unit
sistorized, and utilizes the modern technique of stored- The processing unit (Figure 7) contains the magnetic-
program control. This system can perform all basic core storage unit to store the program data and instruc-
functions (such as: reading, printing, comparing, add- tions and to perform all logic and arithmetic operations.
ing, subtracting, editing) and variations of these func- Alphabetic and numeric characters are represented in
tions. storage by an 8-bit code. The eight bits consist of six
The IBM 1401 incorporates an advanced design of bits for alphameric binary code, a seventh bit for
many outstanding features of existing equipment, for checking, and an eighth bit for field definition.
improved programming and operating efficiency:
1. Core storage provides instant access to information
and the stored program. Every position can accom-
modate either an alphabetic or numeric character,
and is individually addressable. Character time is
.0115 millisecond.
2. Variable word length permits maximum utilization
of the storage facility.
3. High-speed printing increases output efficiency.
4. High-speed reading and punching offer faster input
and output and permit easy integration of the 1401
into existing accounting machine procedures.
5. Editing completes the preparation of information
for printed output.
Physical Features
The physical features of the units that make up the
card-oriented system are compact and of modern de-
sign. The units are mobile to permit an operating
arrangement that is both convenient and efficient. The
IBM 1401 Data Processing System in its card configura-
tion is composed of three interrelated units:
1. IBM 1401 Processing Unit contains 1,400 positions of
alphameric core storage (expandable to 2,000, 4,000,
8,000, 12,000, or 16,000 positions). The processing
unit is the only unit that is changed in physical size
when different system configurations are required.
2. IBM 1402 Card Read-Punch is equipped with either
an 800-card-per-minute read feed and a 250-card-
per-minute punch feed, or a 450-card-per-minute
read feed and 250-card-per-minute punch feed (de-
pending on the model).
3. IBM 1403 Printer is capable of printing as many as
600 or 465 lines per minute (depending on the
model), with a print span of 100, 120, or 132 posi-
tions of alphabetic and numeric data per line, de-
pending on the model. Figure 7. IBM 1401 Processing Unit (Two-Cube and Four-Cube)
11
Three areas of storage are reserved for input and
output data. In the first, 80 storage positions receive CODED ADDRESSES IN STORAGE
80 columns of card information from the card reader.
Another 80 positions are reserved for assembly of data Actual Addresses 3-Character Addresses
to be punched. The third area is reserved for the assem-
000 to 999 No zone bits 000 to 999
bly of 100 (or 132) characters of printer information.
1000 to 1099 tOO to t99
However, when these areas are not being used as spec-
ified, they can be used for other purposes. 1100 to 1199 /00 to /99
1200 to 1299 SOO to S99
NOTE: If 132-character printing is ordered, the additional-
print-control feature is required in the 140l. 1300 to 1399 TOO to T99
1400 to 1499 A-bit, UOO to U99
Each of the storage positions is addressable and
identified by a 3-character address. The first 1,000 posi- 1500 to 1599 using O-zone VOO to V99
tions of storage have the addresses 000-999. The re- 1600 to 1699 WOO to W99
maining storage positions use an alphabetic or special 1700 to 1799 XOO to X99
character in the hundreds position of the address (Fig- 1800 to 1899 YOO to Y99
ure 8). 1900 to 1999 ZOO to Z99
Stored programming involves the concept of words. 2000 to 2099 000 to 099
A word is a single character, or group of characters, 2100 to 2199 JOO to J99
that represents a complete unit of information. One of 2200 to 2299 KOO to K99
the most important characteristics of the IBM 1401 Data
2300 to 2399 LOO to L99
Processing System is its use of the variable-word-length
principle, in which words are not limited to any prede- 2400 to 2499 B-bit, MOO to M99
termined number of character positions in the storage 2500 to 2599 using II-zone NOO to N99
unit. Each word occupies only that number of charac- 2600 to 2699 *000 to 099
ter positions actually needed for each specific instruc- 2700 to 2799 POO to P99
tion, or for t..~e specific data involved. This facility con~
tributes to the high efficiency of the 1401 core-storage
2800
2900
to
to
2899
2999
l QOO to
ROO to
Q99
R99
unit. +
+
3000 to 3099 000 to 099
IBM 1402 Card Read-Punch 3100 to 3199 AOO to A99
The IBM 1402 Card Read-Punch (Figure 9) provides 3200 to 3299 BOO to B99
the card-oriented system with simultaneous punched- 3300 to 3399 COO to C99
card input and output. This unit has two card feeds, 3400 to 3499 A-B-bit, DOO to D99
l
one for reading and one for punching. The read section 3500 to 3599 using 12-zone EOO to E99
has a rated speed of either 800 cards per minute or 450 3600 to 3699 FOO to F99
cards per minute, depending on the model. Actual card 3700 to 3799 G99
speed realized is governed by the program routine for GOO to
3800 to 3899 HOO to H99
each particular run. The read feed is equipped with a
3900 to 3999 100 to 199
device for large-capacity loading, called a file feed. * Letter 0 foil owed by Zero Zero
With the file-feed device, the read feed can be loaded
with as many as 3,000 cards, which reduces operator- Figure 8. Storage Address Codes
attendance requirements.
The 51-column read feed (special feature), inter- transport path, three stackers are available to receive
changeable with the standard 80-column feed, allows the cards. The normal read stacker is the stacker closest
the processing of stub cards, thus increasing the flexi- to the read hopper and is used unless the cards are
bility of the IBM 1401 Data Processing System. program-directed to stackers 1 or 2,
The cards feed through the read side of the machine The punch section has a rated speed of 250 cards
9-edge first, face down. The feed path is from right to per minute, with a card hopper capacity of 2,100 cards.
left, passing two sets of brushes (Figure 10). The read The cards feed 12-edge first, face down. The feed path
check station reads 80 columns of the card to establish is left to right, passing a blank station, a punching sta-
a hole count for checking purposes. The read station tion, and a reading station (Figure 10). The punching
also reads the 80 columns, proves the hole count, and station consists of 80 punches for recording informa-
directs the data into storage. At the end of the card- tion. The punch-reading station counts all the holes in
12 IBM 1401 System Summary
Figure 11. Radial Stackers
No electrical or mechanical coupling exists between
Figure 9. IBM 1402 Card Read-Punch the read and punch units. Therefore, any information
from the read side must be entered into storage and
read out of storage to the punch unit, for operations
all 80 columns of the card, for punch checking. At the equivalent to reproducing or gangpunching.
end of the card transport path on the punch side, three
stackers are available to receive the cards. The normal
IBM 1403 Printer
punch stacker is used unless the cards are program-
directed to stacker 4 or 8. \Vith the addition of punch- The printer (Figure 12) is another output medium for
feed-read (special feature), the source card can be read the 1401 card-oriented system. Units of the 1403 have
in the punch side, and output data can be punched rated printing speeds of 340, 465, or 600 lines per min-
into the same source card. ute, depending on the model. Also, printing capacities
of 100, 120, or 132 positions are available.
All these stackers are of the radial type (Figure 11)
with a capacity of 1,000 cards each. Cards can be re- Horizontal spacing of printed characters is 10 char-
moved from the stackers without stopping the machine. acters to the inch. Vertical spacing of six or eight lines
Two stackers are assigned exclusively to the reader to the inch can be manually selected by the operator.
and two are assigned exclusively to the punch. The Vertical line spacing is performed by either a single-
center or common stacker (8/2 stacker) can be used by speed or a dual-speed tape-controlled carriage. (The
either unit. dual-speed carriage is standard on 1403 printers used
Both feeds are equipped with misfeeding- and jam- in all of the 1401 systems except the 1401 Models A and
detection devices. A card jam or a misfeed in either the G systems.)
read or punch feed causes the 1401 to stop. A console The dual-speed carriage skips lines at the rate of 75
light glows, indicating which feed caused the stop. inches per second after the first eight lines of any skip.
Punches
Punch Read
a
r~~;er I
Blank
Station I Check
-~ ;~~:~:, ;!:~e, 21k ~~i
NormaIUUUUU=
Punch Read
NP 4 8 2 NR
Figure 10. IBM 1402 Card Transport Schematic
13
posite a magnetically driven hammer that presses the
form against the chain.
As each character is printed, checking circuits are
set up to insure that the character printed is correct.
Checks are also made to insure that only valid charac-
ters are printed and that overprinting does not occur.
If an error is detected, the machine stops, and the asso-
ciated check light comes on.
The IBM 1403 Printer has special features that in-
crease operating efficiency. Mobile forms stands allow
blank forms to be loaded and wheeled to the printer
and completed forms to be wheeled away. This reduces
paper handling and job setup time. Forms insertion is
simplified by operator control levers and keys.
I nterleavi n9
The 1401 Model G card system can perform a write-
and-read or a write-and-punch operation in the time
normally required for a read or punch operation (re-
spectively). This simultaneous operation of two units
(printer and either reader or punch) is called inter-
leaving and is unique to the 1401 Model G.
Figure 12. IBM 1403 Printer
Write and Read Operation
The write and read operation is performed by execut-
The single-speed carriage has a skipping speed of 3.3 ing the print operation during the read start time and
inches per second. card reading time of a read cycle. Depending on the
Each position can print 48 different characters: 26 program routine, this operation can result in a card-
alphabetic; 10 numeric; and 12 special characters (& , . read speed and printing speed of 450 cards and lines
o - $ * 9= / % # @ in special-character arrangement per minute.
A or B). The printing format is controlled by the 1401
stored program. The information to be printed is Write and Punch Operation
checked when it is read out to the printer. The alpha- The write and punch operation is performed by execut-
betic, numeric, and special characters are assembled in ing the print operation during the punch start time and
a chain (Figure 13). As the chain travels in a horizontal card punching time of the punch cycle. Depending on
plane, each character is printed as it is positioned op- the program routine, this operation can result in a card-
punch and printing speed of 250 cards and lines per
Type Array
minute.
Write, Read, and Punch Operation
The write, read, and punch operation is not completely
Hammer
interleaved. The write and punch portion of the opera-
tion is interleaved, and the read operation follows the
interleaved operation. This operation results in a print-
ing and card-reading/card-punching speed of 200 cards
and lines per minute.
Armature
Hammer
Magnet
Data Flow
Input to the 1401 card-oriented system is supplied
through the 1402 card read-punch, and output from
the system is provided through the 1402 card read-
Figure 13. Schematic of Printing Mechanism punch (punched-card output) and/or the 1403 printer
14 IBM 1401 System Summary
Four types of address validity checking are per-
formed by the processing unit. Although each of the
four checks has a specific function, each check insures
1401 Processing Unit
that all addresses used in a program are within the
core-storage capacity of the system.
Hole-Count Check
The hole-count feature compares the total number of
punches read in a card column at the first reading sta-
1
1403
tion, with the total number of punches in the same
card column at the second reading station. The hole-
count feature is also effective with the punch side to
Printer
compare the total number of holes set up for punching
in a column, with the number of holes punched in the
card column. If the result of the hole-count comparison
is unequal, in either case, the system stops, and check
Printed lights indicate the unit involved.
Output
Word Mark
Figure 14. Data Flow (Card System) The use of the variable-length instruction and data
format requires a method of determining the instruc-
(printed output). All input data passes through the tion and data-word length. This identification is pro-
1401 processing unit (where arithmetic and logical vided by a word mark.
functions are performed), and all output data passes The word mark serves several functions:
from the processing unit to the particular output unit l. It indicates the beginning of an instruction.
(Figure 14). 2. It defines the size of a data word.
3. It signals the end of execution of an instruction.
NOTE: Word marks are illustrated in this discussion by un-
Checking derlining each character that has an associated word mark.
The IBM 1401 Data Processing System contains many
important design factors to insure maximum efficiency
and reliability. The self-checking features built into Stored-Program Instructions
the 1401 are designed to insure a high degree of error All arithmetic and logical functions are performed by
detection. the instructions retained in storage. One form of an
instruction consists of an operation code followed by
Parity Check two 3-character addresses. The 2-address instruction is
required to move data from one location to another, to
The odd-number bit configuration is used for the par-
perform arithmetic operations of addition or subtrac-
ity check. The proper number of bits for any given
tion, to compare two fields, or to edit.
character is known as parity for that character. A word
Because the 1401 system uses a variable-ward-length
mark that appears with a character is included in the
concept, the length of an instruction can vary from one
check for an odd number of bits.
to eight characters.
\Vhen information is moved within the system, a
parity check is performed to test the presence of an Instruction Format
odd number of bits for each character being moved. Op Code A- or I-address B-address d-character
x xxx xxx x
Validity Check Op Code. This is always a single character that defines
A validity check is performed on all infarmation when the basic operation to be performed. A word mark is
it is read into storage from the card reader, to insure always associated with the operation code position
that all characters are valid. Any invalid character of an instruction.
stops the machine and the associated check light A-Address. This always consists of three characters. It
comes on. can identify the units position of the A-field, or it can
15
be used to select a special unit or feature such as Addressing
tape unit or column-binary feature. The 1401 processes data by following a series of stored
I -address. Instructions that can cause program branches instructions. The storage unit stores both the instruc-
use the I-address to specify the location of the next tions and the data. Each position in storage can be
instruction to be executed if a branch occurs. addressed. The high-order position of a field in storage
is identified by an associated word mark.
B-Address. This is a three-character storage address
that identifies the B-field. It usually addresses the An instruction in core storage is addressed by the lo-
units position of the B-field, but in some operations cation of its high-order position. The machine reads
(such as tape read and write) it specifies the high- the instruction from left to right until it senses the
order position of a record-storage area. word mark associated with the next instruction. The
final instruction in the program must have a word mark
d-Character. The d-character is used to modify an
set at the right of the low-order position. The high-
operation code. It is a single alphabetic, numeric, or
order character is the operation code, with an asso-
special character, positioned as the last character of
ciated word mark that is set by the program when the
an instruction,
instruction cards are loaded. In contrast, a data word
is read from right to left until a word mark is sensed
Instruction Example with its own high-order position. In addressing a data
Op Code A- or I-address B-address word, we specify its units position.
A 072 423
This is an ADD instruction. The operation code A causes Input/Output Storage Assignments
the field whose units position is in storage location 072
to be added to the field whose units position is in loca- Certain areas of storage are reserved for use by input/
tion 423. This operation continues until a word mark output devices (Figure 16). In most cases, the assign-
for the high-order position of field B (which must have ments are such that a correlation is achieved between
a defining word mark) is sensed. The word mark stops input/output columns and/or print positions. The stor-
the operation being performed and causes the program age location assignments are:
to advance to the next instruction. If field A is shorter 001 through 080 card input
than field B, it must also have a defining word mark. 101 through 180 card output
201 through 300 (or 332) print output
As stated before, not all instructions have the 2- 334 through 363 IBM 1404 input (special feature)
address form. Others consist of only one address, or no Except for locations 000 and 100, the areas isolated by
address. This concept results in what is known as vari- these storage assignments can be used for normal proc-
able-length instructions. ' essing or instructions. If the read-compare special fea-
Examples of the six combinations possible in vari- ture for the 1404 is installed, location 333 is used for
able-length instructions are shown in Figure 15. internal programming.
NUMBER OF
POSITIONS OPERATION INSTRUCTION FORMAT
1 READA CARD OP code
,
2 I SELECT STACKER Op code