View source for IBM 1401

{{Short description|1960s decimal computer}}
{{Use mdy dates|date=January 2015}}
{{Infobox CPU architecture
| image      = CHM Demo Room.jpg
| caption    = IBM 1401 at [[Computer History Museum]]
| name       = IBM 1401
| designer   = IBM
| bits       = 6-bits plus word mark and parity
| introduced = 1959
| version    = 
| design     = [[en:Complex_instruction_set_computer|CISC]]
| type       = Memory-Memory
| encoding   = Variable
| branching  = Branch instruction with modifier character
| endianness = [[Big-endian]]
| page size  = 
| extensions = 
| open       = 
| registers  = 3: Instruction Address Register (IAR), Instruction Register (IR), B Register
| gpr        = 
| fpr        = 
}}

The '''IBM 1401''' is a [[variable word length computer|variable-wordlength]] [[decimal computer]] that was announced by [[IBM]] on October 5, 1959. The first member of the highly successful [[IBM 1400 series]], it was aimed at replacing [[unit record equipment]] for processing data stored on [[punched card]]s and at providing peripheral services for larger computers.<ref>{{cite book
 |title=IBM's Early Computers
 |last1=Boshe |first1=Charles J.|last2=Johnson|first2=Lyle R.|last3=Palmer|first3=John H.|last4=Pugh|first4=Emerson W.
 |publisher=MIT Press |year=1986
 |page=473
 |quote=... configured for stand-alone use as well as peripheral service for larger computers ... A small configuration, without tapes and with the minimum memory capacity, was available for just under $2500 per month, a much lower rental for much higher performance than three [[IBM 407|407]] accounting machines plus a [[IBM 604|604]] calculator.}}</ref> The 1401 is considered by IBM to be the [[Ford Model T|Ford Model-T]] of the computer industry due to its mass appeal.<ref>{{Cite web |title=The IBM 1401 |url=https://www.ibm.com/history/1401 |access-date=2024-01-05 |website=www.ibm.com |language=en-us}}</ref> Over 12,000 units were produced and many were leased or resold after they were replaced with newer technology. The 1401 was withdrawn on February 8, 1971.

==History==
[[File:IBM1401 729Tape 1405Disk 1407Console COLOR.jpg|thumb|280px|IBM 1401 Data Processing System. From the left: [[IBM 1402|1402]] Card Read-Punch, 1406 Storage Unit, 1405 RAMAC Disk Unit, 1407 Console Inquiry Station, 1401 Processing Unit, two [[IBM 729|729]] Magnetic Tape Units, [[IBM 1403|1403]] Printer. (courtesy of IBM Archives)]] 
The 1401 project evolved from an IBM project named "World Wide Accounting Machine" (WWAM), which in turn was a reaction to the success of the [[Bull Gamma 3]].<ref>{{Cite web |title=Origins of Architecture and Design of the 1401 |url=https://ibm-1401.info/1401Origins.html |access-date=2023-07-28 |website=ibm-1401.info}}</ref>

The 1401 was used as an independent system in conjunction with IBM punched card equipment. It was also operated as auxiliary equipment to [[IBM 700/7000 series|IBM 700 or 7000 series]] systems.<ref name="ibmarchives">{{cite web |title= 1401 Data Processing System |date= October 5, 1959 |work= IBM Archives |url= http://www.IBM.com/ibm/history/exhibits/mainframe/mainframe_PP1401.html |access-date= June 2, 2010 }}</ref>

Monthly rental for 1401 configurations started at US$2,500 (worth about ${{formatnum:{{Inflation|US|2500|1959|r=-2}}}} today).<ref>{{Cite web|url=http://www.columbia.edu/cu/computinghistory/1401.html|title=The IBM 1401|website=www.columbia.edu|accessdate=March 28, 2024}}</ref> Demand exceeded expectations.

"IBM was pleasantly surprised (perhaps shocked) to receive 5,200 orders in just the first five weeks &ndash; more than predicted for the entire life of the machine!"<ref name=chm>{{cite web |url=http://www.computerhistory.org/core/pdf/ibm_1401.pdf |title=Back to Life: The story behind CHM's IBM 1401 Restoration |author=Spicer, Dag |publisher=Computer History Museum |access-date=May 27, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20101105110749/http://www.computerhistory.org/core/pdf/ibm_1401.pdf |archive-date=November 5, 2010 |df=mdy-all }}</ref>  By late 1961, the 2000 units installed in the USA were about one quarter of all electronic [[stored-program computer]]s by all manufacturers. The number of installed 1401s peaked above 10,000 in the mid-1960s.  "In all, by the mid-1960s nearly half of all computer systems in the world were 1401-type systems."<ref name=chm/>  The system was marketed until February 1971.<ref>{{cite web |title= FAQ's for Products and Services |work= IBM Archives |date= June 11, 2001 |url= http://www.IBM.com/ibm/history/reference/faq_0000000011.html |access-date= June 2, 2010 }}</ref>

Commonly used by small businesses as their primary data processing machines, the 1401 was also frequently used as an off-line [[peripheral]] controller for [[mainframe computer]]s. In such installations, with an [[IBM 7090]] for example, the mainframe computers used only [[magnetic tape]] for input-output. It was the 1401 that transferred input data from slow peripherals (such as the [[IBM 1402]] Card Read-Punch) to tape, and transferred output data from tape to the card punch, the [[IBM 1403]] Printer, or other peripherals. This allowed the mainframe's throughput to not be limited by the speed of a card reader or printer. 
(For more information, see [[spooling]].) Some later installations (e.g., at NASA) included the 1401 as a front-end peripherals controller to an IBM 7094 in a Direct Coupled System (DCS).

Elements within IBM, notably [[John Haanstra]], an executive in charge of 1401 deployment, supported its continuation in larger models for evolving needs (e.g., the [[IBM 1410]]) but the 1964 decision at the top to focus resources on the [[System/360]] ended these efforts rather suddenly.

IBM was facing a competitive threat from the [[Honeywell 200]]<ref>among other things, Honeywell used the name [[Easycoder]], resembling IBM's [[Autocoder]].</ref><ref>there was also a semi-automated converter of 1401 object code, named Liberator: {{cite web
   |url=http://ibm-1401.info/1401-Competition.html#UsingLib
   |title=Using Liberator}}</ref> and the 360's incompatibility with the 1401 design. IBM pioneered the use of [[microcode]] [[Emulator|emulation]], in the form of [[Read-only memory#Other technologies|ROM]], so that some System/360 models could run 1401 programs.<ref>{{cite book
   |title=Building IBM: Shaping an Industry and Its Technology 
   |author=Emerson W. Pugh |year=1995 |publisher=MIT 
   |isbn=0-262-16147-8 |page=273}}</ref>[[File:IBM 1401 signal tracing at CHM.jpg|thumb|A volunteer repairing a 1401 at the [[Computer History Museum]]]]

Due to its popularity and mass-production, the IBM 1401 was often considered to be the first electronic [[mainframe computer]] to be introduced in various countries, such as [[Singapore]] (1963; for the [[Central Provident Fund|Central Provident Fund Board]])<ref>{{cite web | url=https://www.smartnation.gov.sg/about-smart-nation/our-journey/milestones/ | title=Milestones }}</ref> and [[South Korea]] (1967; for the [[Ministry of Economy and Finance (South Korea)|Economic Planning Board]]).<ref>[https://www.ibm.com/ibm/history/ibm100/us/en/icons/mainframe/transform/ Mainframe transform]ibm.com {{Webarchive|url=https://web.archive.org/web/20230815083313/https://www.ibm.com/ibm/history/ibm100/us/en/icons/mainframe/transform/ |date=August 15, 2023 }}</ref><ref>서현진. (1997). 처음쓰는 한국컴퓨터사 (서울: 전자신문사).</ref> During the 1970s, IBM installed many 1401s in [[India]] and [[Pakistan]] where they were in use well into the 1980s.

Two 1401 systems have been restored to operating order at the [[Computer History Museum]] in [[Mountain View, California]].<ref>{{cite web | title = 1401 Restoration Project | url = http://IBM-1401.info/index.html }}</ref><ref>{{cite web | title = 1401 "Rebuilding the IBM," by Philip E. Ross, IEEE Spectrum, November 2009 | url = https://spectrum.ieee.org/computing/hardware/rebuilding-the-ibm-1401| archive-url = https://web.archive.org/web/20091103110802/http://spectrum.ieee.org/computing/hardware/rebuilding-the-ibm-1401| url-status = dead| archive-date = November 3, 2009}}</ref>

==Architecture==
[[File:IBM 1401 Control Panel.jpg|thumb|1401 Console and, below, the Auxiliary Console.]]

Each alphanumeric character in the 1401 is encoded by six [[bit]]s, called ''B,A,8,4,2,1''.  The ''B,A'' bits are called ''zone'' bits and the ''8,4,2,1'' bits are called ''numeric'' bits, terms taken from the [[Punched card#IBM 80-column format and character codes|IBM 80 column punched card]].

* For digits 1 through 9, the bits ''B,A'' are zero, the digit [[Binary-coded decimal|BCD]] encoded in bits ''8,4,2,1''.  Digit 0 is encoded ''8,2''.
* For alphabetic characters the setting of bits is derived from the zone and digit punches of the [[Punched card#IBM 80-column format and character codes|IBM 80 column punched card character code]]: ''B,A'' from ''12'', ''B'' from ''11'', and ''A'' from ''0''; the setting of bits ''8,4,2,1'' from BCD encoding of the 1 through 9 punches. Thus the letter A, ''12,1'' in the punched card character code, is encoded ''B,A,1''.
* Encodings of punched card characters with two or more digit punches can be found in the [[IBM 1401#Character and op codes|character and op codes]] table.

IBM called the 1401's character code BCD ("binary-coded decimal"), even though that term describes only the decimal digit encoding.<ref>[[binary-coded decimal#IBM and BCD|IBM and BCD]]</ref>  The 1401's alphanumeric collating sequence is compatible with the punched card collating sequence.

Associated with each memory location are two other bits, called ''C'' for odd [[parity bit|parity check]] and ''M'' for [[Word mark (computer hardware)|word mark]]. ''M'' is present in memory but not on punched cards, and has to be set using special machine instructions; when printing memory it is typically displayed by underlining the character. ''C'' is calculated automatically and is also not present on punched cards.

Each memory location then, has the following bits:

''C B A 8 4 2 1 M''

The 1401 was available in six [[core memory|memory]] configurations: 1,400, 2,000, 4,000, 8,000, 12,000, or 16,000 characters.{{efn|The 1401 is a decimal computer, so e.g. "8000" characters is not 8,192 characters.}} Each character is addressable, addresses ranging from 0 through 15999. A very small number of 1401s were expanded to 32,000 characters by special request.<ref>{{Cite book|last=Fedorkow|first=Guy|url=http://ibm-1401.info/IBM-1401-Theory-of-Operation-GF.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://ibm-1401.info/IBM-1401-Theory-of-Operation-GF.pdf |archive-date=2022-10-10 |url-status=live|title=IBM 1401AModernTheory of Operation|year=2015|pages=143}}</ref>

Some operations use specific memory locations (those locations are not reserved and can be used for other purposes).  ''Read a card'' stores the 80 columns of data from a card into memory locations 001–080.  Index registers 1, 2 and 3 are in memory locations 087–089, 092-094 and 097-099 respectively. ''Punch a card'' punches the contents of memory locations 101-180 into a card. ''Write a line'' prints the contents of memory locations 201–332.

The 1401's [[Instruction set|instruction]] format is

   Opcode
    with   &#91;A-or-I-or-unit-address &#91;B-address&#93;&#93; &#91;modifier&#93;
  word mark

[[Opcode]]s are one character.  Memory addresses ("I" a branch target, "A" and "B" data) and unit address are three characters.  The opcode modifier is one character.  Instruction length is then 1, 2, 4, 5, 7, or 8 characters.  Most instructions have to be followed by a word mark (a requirement commonly met by the word mark with the opcode of the next instruction).

See [[#Character and op codes|Character and op codes]] for a list of operations.

A three-character memory address in an instruction is an encoding of a five-digit memory address.  The three low-order digits of the five-digit address, 000 to 999, are specified by the numeric bits of the three characters.  The zone bits of the high-order character specify an increment as follows: ''A'' 1000, ''B'' 2000, ''B'' and ''A'' together 3000, giving an addressability of 4,000 memory locations.  The zone bits of the low-order character specify increments of 4000, 8000, or 12000, to address 16,000 memory locations (with an [[IBM 1406]] Storage Unit).{{efn|More simply stated: the four zone bits encoded the decimal values 0 to 15 as the binary numbers 0000 to 1111.  The encoded value is used as the thousands part of a 1401 address.  Thus making the 1401 a curious machine with memory addresses stored as a combination of 3 decimal  digits and 4 binary digits.  IBM did not use the word "binary" in describing the 1401's addressing (see the 1401 Reference Manual).}}  For example, the three-character address "I99" is a reference to memory location 3000 + 999, or 3999.

The zone bits of the middle character of a three-character memory address can specify one of three [[index register]]s, one of many optional features.

Operands referenced by the A-address and B-address can be: a single memory location, a variable-length field, or a variable-length record.  Variable-length fields are addressed at their low-order (highest-addressed) position, their length defined by a [[word mark (computer hardware)|word mark]] set at their high-order (lowest-addressed) position. When an operation such as addition is performed, the processor begins at the low-order position of the two fields and works its way to the high-order, just as a person would when adding with pencil and paper.

The only limit on the length of such fields is the available memory.  Instructions applicable to variable-length fields include: ''Add'', ''Subtract'', ''Multiply'', ''Divide'', ''Compare'', ''Move Characters to A or B Word Mark'', ''Move Characters and Edit''.  One or more adjacent variable-length fields can make up a variable-length record.  A variable-length record is addressed at its high-order position, its length defined by a [[Groupmark character|group-mark]] character with a word mark or a [[Recordmark character|record-mark]] character in its low-order  position. The instruction ''Move Characters Record or Group Mark'' can be used to assemble a block of records.  A variable-length record, or block of records, to be written to magnetic tape is addressed at its high-order position, its length defined by a group-mark character with a word mark immediately following its low-order position.

A sequence of operations on adjacent fields can be "chained", using the addresses left in the address registers by the previous operation.  For example, addition of adjacent data fields might be coded as <code><u>A</u> 700,850</code>, <code><u>A</u> 695,845</code>, <code><u>A</u> 690,840</code>.  With chaining, this can be coded as <code><u>A</u> 700,850</code>, <code><u>A</u></code>, <code><u>A</u></code> - omitting data address from the second and third instructions.<ref>{{cite book |author =IBM |title =IBM 1401 Data Processing System: Reference Manual |date =April 1962 |id =A24-1403-5 |page =20 |url =http://bitsavers.org/pdf/ibm/140x/A24-1403-5_1401_Reference_Apr62.pdf |url-status =dead |archive-url =https://web.archive.org/web/20100809033646/http://www.bitsavers.org/pdf/ibm/140x/A24-1403-5_1401_Reference_Apr62.pdf |archive-date =August 9, 2010 |df =mdy-all }}</ref>

===IBM 1401G===
The IBM 1401G was sold in six models: (G1 and G11: 1,400 ''storage positions''; G2 and G12 for 2,000; G3 and G13 for 4,000).
<ref>IBM 1401G, booklet 520-1061-0</ref> One difference between the 1401 and 1401G is how the reader-punch is controlled.<ref>{{cite web
   |url=http://www.textfiles.com/bitsavers/pdf/ibm/140x/A24-3067-2_1401_1460_System_Operation_Reference_Manual_Sep66.pdf |archive-url=https://web.archive.org/web/20150403205906/http://www.textfiles.com/bitsavers/pdf/ibm/140x/A24-3067-2_1401_1460_System_Operation_Reference_Manual_Sep66.pdf |archive-date=2015-04-03 |url-status=live
   |title=System Operation Reference Manual. IBM 1401. IBM 1460}}</ref>

==Booting and sample program==
When the '''LOAD''' button on the 1402 Card Read-Punch is pressed, a card is read into memory locations 001–080, a word mark is set in location 001 to indicate that it is an executable instruction, the word marks in locations 002-080 (if any) are cleared, and execution starts with the instruction at location 001.  That is always the {{wt|en|dyadic}} ''Set Word Mark'', to set word marks on the two following words (instructions). A single ''Set Word Mark'' instruction can set two word marks but requires one word mark to have been on itself, so a sequence of these instructions are needed, which incrementally set word marks in the program's code or data, and set word marks for subsequent ''Set Word Mark'' instructions. Execution of instructions in the card continues, setting word marks, loading the program into memory, and then branching to the program's start address.  To read subsequent cards, an explicit ''Read'' command (opcode <code>1</code>) must be executed as the last instruction on every card to get the new card's contents into locations 001–080.  Note that the word marks are '''not''' erased when the ''Read'' command is executed, but are kept as-is for the next card read in.  This is convenient, because much of what the first few cards do is set word marks in the proper locations; having the first half dozen or so word marks set means the programmer does not need to set those word marks again.

<!-- the intent is that a "fixed word length" programmer with a little motivation, reading this for the first time, can follow the program's execution, understanding both the word marks and the commands. -->
One-card programs can be written for various tasks.  Commonly available were a one-card program to print the deck of cards following it, and another to duplicate a deck to the card punch. See Tom Van Vleck's web site.<ref>{{cite web | title = Tom Van Vleck: 1401s I have known | url = http://www.multicians.org/thvv/1401s.html }}</ref> Here is a one-card program which will print "HELLO, WORLD!".  Pressing LOAD (above) reads one card, and begins execution at 001 (the first <code>,</code>). The program will automatically set its own wordmarks, assuming that the first <code>,</code> has a wordmark already.

:<code><u>,</u>036008<u>,</u>040015<u>,</u>044022<u>,</u>051029<u>,</u>052053<u>/</u>299<u>/</u>332<u>L</u>065213<u>2.H</u>ELLO, WORLD!</code>

Following conventional IBM notation, the underscores{{clarify|date=September 2021}} show where word marks are set in memory once the program has run; on punched cards they would not be indicated visually or present in the punched data.

The program is:
* ''Set Word Mark'' (opcode <code>,</code> operands 036 008). This must always be the first instruction, and one of its operands must always be 008 or else the next instruction would not have a word mark to indicate that it is an executable instruction.
* Additional ''Set Word Mark''s. The underscores show where the word marks are after completing all <code>,</code> opcodes. Only word marks from 036 and further are needed for the "guts" of the program; word marks up through 029 are only needed for ''Set Word Mark'' instructions. Since the core of the program needs six word marks, five ''Set Word Mark'' instructions are needed in total. The reason one fewer is needed is because the final ''Set Word Mark'' does not need to waste an operand on other ''Set Word Marks''
* ''Clear Storage'' - the rest of the print area 299-200 (opcode <code>/</code> operand 299)
* ''Clear Storage'' - part of the print area 332-300 (opcode <code>/</code> operand 332)
* ''Move'' <code>HELLO, WORLD!</code> to the print area (opcode <code>L</code>, operands 065 and 213. ''Move'' stops due to the word mark in location 052 (which, doing double-duty, also defines the end of the ''Halt'' and branch instruction))
* ''Write a Line'' on the printer (opcode <code>2</code>; "HELLO, WORLD!" will be printed in the 13 leftmost printer positions)
* ''Halt'' (opcode <code>.</code>)

==Hardware implementation==
{{main | transistor computer}}

[[File:IBM 1401 card cage.jpg|thumb|Closeup of a swing-out card cage (or ''gate'' in IBM parlance) showing some of the 1401's [[IBM Standard Modular System|SMS circuit cards]]]]
Most of the logic circuitry of the 1401 is a type of [[diode–transistor logic]] (DTL), that IBM referred to as ''CTDL (Complemented Transistor Diode Logic)''. Other IBM circuit types were referred to as: ''Alloy'' (some logic, but mostly various non-logic functions, named for the germanium-alloy transistors used), ''CTRL'' (''Complemented Transistor Resistor Logic'', a type of [[resistor–transistor logic]] (RTL)). Later upgrades (e.g., the TAU-9 tape interface) use a faster type of DTL using [[drift-field transistor|"drift" transistor]]s (a type of transistor invented by [[Herbert Kroemer]] in 1953) for their speed, that IBM referred to as ''SDTDL (Saturated Drift Transistor Diode Logic)''. Typical logic levels of these circuits were (S & U Level) high: 0&nbsp;V to -0.5V, low: -6&nbsp;V to -12&nbsp;V; (T Level) high: 6&nbsp;V to 1&nbsp;V, low: -5.5&nbsp;V to -6&nbsp;V.

These circuits are constructed of discrete components (resistors, capacitors, transistors) mounted on single-sided paper-epoxy [[printed circuit board]]s either {{convert|2.5|by|4.5|in|mm}} with a 16-pin [[gold-plated]] edge connector (single wide) or {{convert|5.375|by|4.5|in|mm}} with two 16-pin gold-plated edge connectors (double wide), that IBM referred to as ''SMS'' cards ([[Standard Modular System]]). The amount of logic on one card is similar to that in one [[7400 series]] [[Integrated circuit#SSI|SSI]] or simpler [[Integrated circuit#MSI|MSI]] package (e.g., three to five logic gates or a couple of [[Flip-flop (electronics)|flip-flops]] on a single-wide card up to about twenty logic gates or four flip-flops on a double-wide card).

[[File:SMScard.jpg|thumb|left|A single-width SMS card of the type used in the 1401]]
The SMS cards were inserted in sockets on hinged swing-out racks, that IBM referred to as ''gates''.

The modules used were fairly delicate, compared to previous unit-record equipment, so IBM shipped them enclosed in a newly invented packing material, [[bubble wrap]].  This was one of the first widespread uses of this packing; it greatly impressed recipients, and brought great publicity to the material.

Like most machines of the day, the 1401 uses [[magnetic-core memory]]. The cores are about 1&nbsp;mm in diameter and use a four-wire arrangement (x, y, sense, and inhibit).
The memory is arranged in planes of {{not a typo|4000}} <!-- NOT 4096. This was a decimal-addressed machine. -->
cores each, each core storing one bit. A stack of eight such planes store the six data bits, word mark bit, and parity bit for 4000 memory locations. Together with eight additional planes with fewer cores on them for additional storage functions, this made up a 4000-character  memory module.<ref>{{cite web
 |url=http://members.optushome.com.au/intaretro/1401Core.htm
 |title=Core memory frame from a 1401
 |author=Rob Storey
 |access-date=July 15, 2012
 |archive-date=July 16, 2012
 |archive-url=https://web.archive.org/web/20120716203935/http://members.optushome.com.au/intaretro/1401Core.htm
 |url-status=dead
 }}</ref> One such module is housed within the 1401's primary enclosure. Systems were commonly available with two, three, or four such modules. The additional modules are contained in an add-on box, the 1406 Core Memory Unit, which is about two feet square and three feet high.

[[File:IBM 1403 opened up2.jpg|thumb|120px|1403 line printer opened, with 729 tape drives in the background.]]

Operands in memory are accessed serially, one memory location at a time, and the 1401 can read or write one memory location within its basic cycle time of 11.5 microseconds.<ref>{{cite web
 |url=http://www.ibm-1401.info/1401GuidePosterV9.html
 |title=The IBM 1401
 |work=IBM 1401 Restoration Project   |publisher=Computer History Museum
 |access-date=July 15, 2012
 |quote=The 1401’s clock frequency is 86,957 cycles per second, or about 87 kiloHertz! This corresponds to an 11.5 micro-second system clock cycle time. ... The 1401 CPU does everything in a character-serial manner. In order to add say two N-digit numbers, the CPU takes several cycles to fetch the instruction itself and then one cycle for every character of the instruction’s two operands or arguments, or 2N cycles total.}}</ref>

All instruction timings are cited in multiples of this cycle time.<ref>{{cite web
 |url=http://ibm-1401.info/IBM-PrinProg-07.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://ibm-1401.info/IBM-PrinProg-07.pdf |archive-date=2022-10-10 |url-status=live
 |title=IBM 1401 Principles of Programming, Section 7
 |year=1961   |work=IBM Personal Study Program   |publisher=IBM Corporation
 |page=19   |access-date=July 15, 2012
 |quote=The timing of the IBM 1401 is described in terms of the time required for one complete core storage cycle, which is 11.5 microseconds ... The time required for any internal processing instruction is always a multiple of this interval of time.}}</ref>

==IBM 1403 printer==
[[File:IBM 729 restored.jpg|thumb|120px|A reel of half-inch [[magnetic tape|tape]] being loaded onto an [[IBM 729]] tape drive. An [[IBM 1403]] line printer is in the foreground.]]
{{Main|IBM 1403}}
The IBM 1403 printer was introduced in October 1959 with the 1401 Data Processing System. The printer was a completely new development.

==Software==
IBM software for the 1401 included:

* [[IBM 1401 Symbolic Programming System|1401 Symbolic Programming System]] assembler.
* [[Autocoder]] on Tape, a more advanced assembler, required at least 4000-character memory and four tape drives.
* Autocoder on Disk, similar to, but not compatible with, Autocoder on Tape, required at least one 1311 disk drive.
* [[COBOL]] required at least 4000-character memory and four tape drives.
* [[FARGO (programming language)|FARGO]] (Fourteen-o-one Automatic Report Generation Operation), a predecessor of RPG, required at least 4000-character memory.
* [[Fortran#History|FORTRAN II]] required at least 8000-character memory; the 1401 Fortran compiler is described in Haines, L.H. (1965), below. The Fortran compiler, to generate code for small memories, used a pioneering form of interpreted "[[p-code machine|p-code]]" although its programmers had no name for what it was that they did.
* [[FORTRAN IV]] required at least 12000-character memory and either four tape drives or at least one [[IBM 1311]] disk drive.
* [[IBM RPG|RPG]] (Report Program Generator); Basic RPG required at least 4000-character memory.

For the IBM Catalog of 1401 software, see [[IBM 1400 series]].
<!---- used "See ..." rather than copying the reference here since much the software runs on more than one machine and it would be better to have details in one place (assuming the descriptions of software at the 1400 series article will grow).

Should the items here be moved to the 1400 series article? Put another way, do the above items apply to the 1440? 1460?? --->

==Character and op codes==
{{SpecialChars}}

The 1401's operation codes are single characters. In many cases, particularly for the more common instructions, the character chosen is [[mnemonic]] for the operation: A for add, B for branch, S for subtract, etc.

{{hidden begin
|title = Table of character and op codes
|titlestyle = background:#ccccff;
}}

The table is in Character [[Collation|Collating]] Sequence.

: Note: If Word mark bit is set, then the ''C'' bit will be opposite of shown. The ''C'' bit is determined and checked automatically by the machine - normally it is of no concern to the programmers. The only way the ''C'' bit can be entered is by manually using the switches on the Auxiliary Console.  <!-- deleted "for CE" use, see LRM p.116-->A programmer might use these switches to make quick patches while debugging.

{| class="wikitable"
|-
! [[Binary-coded decimal#IBM and BCD|BCD]] Character
! Print-A
! Print-H
! &nbsp;Card&nbsp;
! BCD
w/o M
! Operation
! ''Definition'' & Notes
|-
| align="center" | Blank
| align="center" | &nbsp;
| align="center" | &nbsp;
| &nbsp;
| <code>C&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | .
| align="center" | .
| align="center" | .
| 12-3-8
| <code>&nbsp;BA8&nbsp;21</code>
| Halt
| &nbsp;
|-
| align="center" | ⌑
| align="center" | ⌑
| align="center" | )
| 12-4-8
| <code>CBA84&nbsp;&nbsp;</code>
| Clear Word Mark
| ''Lozenge''
|-
| align="center" | <nowiki>[</nowiki>
| align="center" | &nbsp;
| align="center" | &nbsp;
| 12-5-8
| <code>&nbsp;BA84&nbsp;1</code>
| &nbsp;
| &nbsp;
|-
| align="center" | <
| align="center" | &nbsp;
| align="center" | &nbsp;
| 12-6-8
| <code>&nbsp;BA842&nbsp;</code>
| &nbsp;
| ''Less Than''
|-
| align="center" | ⯒
| align="center" | &nbsp;
| align="center" | &nbsp;
| 12-7-8
| <code>CBA8421</code>
| &nbsp;
| ''Group Mark''
|-
| align="center" | &
| align="center" | &
| align="center" | +
| 12
| <code>CBA&nbsp;&nbsp;&nbsp;&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | $
| align="center" | $
| align="center" | $
| 11-3-8
| <code>CB&nbsp;8&nbsp;21</code>
| &nbsp;
| &nbsp;
|-
| align="center" | *
| align="center" | *
| align="center" | *
| 11-4-8
| <code>&nbsp;B&nbsp;84&nbsp;&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | <nowiki>]</nowiki>
| align="center" | &nbsp;
| align="center" | &nbsp;
| 11-5-8
| <code>CB&nbsp;84&nbsp;1</code>
| &nbsp;
| &nbsp;
|-
| align="center" | ;
| align="center" | &nbsp;
| align="center" | &nbsp;
| 11-6-8
| <code>CB&nbsp;842&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | Δ
| align="center" | &nbsp;
| align="center" | &nbsp;
| 11-7-8
| <code>&nbsp;B&nbsp;8421</code>
| &nbsp;
| ''Delta'' (Mode Change)
|-
| align="center" | -
| align="center" | -
| align="center" | -
| 11
| <code>&nbsp;B&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | /
| align="center" | /
| align="center" | /
| 0-1
| <code>C&nbsp;A&nbsp;&nbsp;&nbsp;1</code>
| Clear Storage
| &nbsp;
|-
| align="center" |,
| align="center" |,
| align="center" |,
| 0-3-8
| <code>C&nbsp;A8&nbsp;21</code>
| Set Word Mark
| &nbsp;
|-
| align="center" | %
| align="center" | %
| align="center" | (
| 0-4-8
| <code>&nbsp;&nbsp;A84&nbsp;&nbsp;</code>
| Divide
| Optional special feature.
|-
| align="center" | ˠ
| align="center" | &nbsp;
| align="center" | &nbsp;
| 0-5-8
| <code>C&nbsp;A84&nbsp;1</code>
| &nbsp;
| ''Word Separator''
|-
| align="center" | \
| align="center" | &nbsp;
| align="center" | &nbsp;
| 0-6-8
| <code>C&nbsp;A842&nbsp;</code>
| &nbsp;
| ''Left Oblique''
|-
| align="center" | ⧻
| align="center" | &nbsp;
| align="center" | &nbsp;
| 0-7-8
| <code>&nbsp;&nbsp;A8421</code>
| &nbsp;
| ''Tape Segment Mark''
|-
| align="center" | ƀ
| align="center" | ‡
| align="center" | ‡
| bgcolor="C0C0C0" | N/A
0
&nbsp;
| <code>&nbsp;&nbsp;A&nbsp;&nbsp;&nbsp;&nbsp;</code>
| &nbsp;
| Cannot be read from card without a no-cost [[Request price quotation|RPQ]], in which case it is read as 8–2.{{efn|The RPQ "Reader/Punch Card Code 8-2 and A-Bit Compatibility" (898148) causes the 1401 to read/punch the A bit as 8-2 for compatibility with the IBM 1410.<ref>{{cite web|title=Custom Features for IBM 1401, 1440, and 1460 Data Processing Systems |url=http://bitsavers.org/pdf/ibm/140x/A24-3315-0_1401customFeatur.pdf |access-date=September 23, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20120829025513/http://www.bitsavers.org/pdf/ibm/140x/A24-3315-0_1401customFeatur.pdf |archive-date=August 29, 2012 |df=mdy-all }}</ref>}}
Punches as zero (or 8–2 with the RPQ).
''Blank with "even-parity"'' on tape.
|-
| align="center" | #
| align="center" | #
| align="center" | =
| 3-8
| <code>&nbsp;&nbsp;&nbsp;8&nbsp;21</code>
| Modify Address
| Optional (requires more than
4000 characters of memory)
|-
| align="center" | @
| align="center" | @
| align="center" | '
| 4-8
| <code>C&nbsp;&nbsp;84&nbsp;&nbsp;</code>
| Multiply
| Optional special feature.
|-
| align="center" | :
| align="center" | &nbsp;
| align="center" | &nbsp;
| 5-8
| <code>&nbsp;&nbsp;&nbsp;84&nbsp;1</code>
| &nbsp;
| &nbsp;
|-
| align="center" | >
| align="center" | &nbsp;
| align="center" | &nbsp;
| 6-8
| <code>&nbsp;&nbsp;&nbsp;842&nbsp;</code>
| &nbsp;
| ''Greater Than''
|-
| align="center" | √
| align="center" | &nbsp;
| align="center" | &nbsp;
| 7-8
| <code>C&nbsp;&nbsp;8421</code>
| &nbsp;
| ''Tape Mark''
|-
| align="center" | ?
| align="center" | &
| align="center" | &
| 12-0
| <code>CBA8&nbsp;2&nbsp;</code>
| Zero and Add
| ''Plus Zero''
|-
| align="center" | A
| align="center" | A
| align="center" | A
| 12-1
| <code>&nbsp;BA&nbsp;&nbsp;&nbsp;1</code>
| Add
| &nbsp;
|-
| align="center" | B
| align="center" | B
| align="center" | B
| 12-2
| <code>&nbsp;BA&nbsp;&nbsp;2&nbsp;</code>
| Branch or Branch on Indicator 
| See [[IBM 1401#Modifiers for five-character Branch On Indicator (B) instruction|"Modifiers for five-character Branch on Indicator (B) instruction"]] section
|-
| align="center" | C
| align="center" | C
| align="center" | C
| 12-3
| <code>CBA&nbsp;&nbsp;21</code>
| Compare
| &nbsp;
|-
| align="center" | D
| align="center" | D
| align="center" | D
| 12-4
| <code>&nbsp;BA&nbsp;4&nbsp;&nbsp;</code>
| Move Numerical
| (Bits)
|-
| align="center" | E
| align="center" | E
| align="center" | E
| 12-5
| <code>CBA&nbsp;4&nbsp;1</code>
| Move Characters and Edit
| &nbsp;
|-
| align="center" | F
| align="center" | F
| align="center" | F
| 12-6
| <code>CBA&nbsp;42&nbsp;</code>
| Control Carriage
| (Printer)
|-
| align="center" | G
| align="center" | G
| align="center" | G
| 12-7
| <code>&nbsp;BA&nbsp;421</code>
| &nbsp;
| &nbsp;
|-
| align="center" | H
| align="center" | H
| align="center" | H
| 12-8
| <code>&nbsp;BA8&nbsp;&nbsp;&nbsp;</code>
| Store B-Address Register
| Optional special feature.
|-
| align="center" | I
| align="center" | I
| align="center" | I
| 12-9
| <code>CBA8&nbsp;&nbsp;1</code>
| &nbsp;
| &nbsp;
|-
| align="center" | !
| align="center" | -
| align="center" | -
| 11-0
| <code>&nbsp;B&nbsp;8&nbsp;2&nbsp;</code>
| Zero and Subtract
| ''Minus Zero''
|-
| align="center" | J
| align="center" | J
| align="center" | J
| 11-1
| <code>CB&nbsp;&nbsp;&nbsp;&nbsp;1</code>
| &nbsp;
| &nbsp;
|-
| align="center" | K
| align="center" | K
| align="center" | K
| 11-2
| <code>CB&nbsp;&nbsp;&nbsp;2&nbsp;</code>
| Select Stacker and other device controls
| See [[IBM 1401#Modifiers for Select Stacker (K) instruction|"Modifiers for Select Stacker (K) instruction"]] section
|-
| align="center" | L
| align="center" | L
| align="center" | L
| 11-3
| <code>&nbsp;B&nbsp;&nbsp;&nbsp;21</code>
| Load Characters to Word Mark
| &nbsp;
|-
| align="center" | M
| align="center" | M
| align="center" | M
| 11-4
| <code>CB&nbsp;&nbsp;4&nbsp;&nbsp;</code>
| Move Characters to Word Mark
| &nbsp;
|-
| align="center" | N
| align="center" | N
| align="center" | N
| 11-5
| <code>&nbsp;B&nbsp;&nbsp;4&nbsp;1</code>
| No Operation
| &nbsp;
|-
| align="center" | O
| align="center" | O
| align="center" | O
| 11-6
| <code>&nbsp;B&nbsp;&nbsp;42&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | P
| align="center" | P
| align="center" | P
| 11-7
| <code>CB&nbsp;&nbsp;421</code>
| Move Characters to
Record or Group Mark
| Optional special feature.
|-
| align="center" | Q
| align="center" | Q
| align="center" | Q
| 11-8
| <code>CB&nbsp;8&nbsp;&nbsp;&nbsp;</code>
| Store A-Address Register
| Optional special feature.
|-
| align="center" | R
| align="center" | R
| align="center" | R
| 11-9
| <code>&nbsp;B&nbsp;8&nbsp;&nbsp;1</code>
| &nbsp;
| &nbsp;
|-
| align="center" | ‡
| align="center" | ‡
| align="center" | ‡
| 0-2-8
| <code>&nbsp;&nbsp;A8&nbsp;2&nbsp;</code>
| &nbsp;
| ''Record Mark''
|-
| align="center" | S
| align="center" | S
| align="center" | S
| 0-2
| <code>C&nbsp;A&nbsp;&nbsp;2&nbsp;</code>
| Subtract
| &nbsp;
|-
| align="center" | T
| align="center" | T
| align="center" | T
| 0-3
| <code>&nbsp;&nbsp;A&nbsp;&nbsp;21</code>
| Translate
| (1460 only)
|-
| align="center" | U
| align="center" | U
| align="center" | U
| 0-4
| <code>C&nbsp;A&nbsp;4&nbsp;&nbsp;</code>
| Control Unit
| (Tape)
|-
| align="center" | V
| align="center" | V
| align="center" | V
| 0-5
| <code>&nbsp;&nbsp;A&nbsp;4&nbsp;1</code>
| Branch if Word Mark
and/or Zone
| &nbsp;
|-
| align="center" | W
| align="center" | W
| align="center" | W
| 0-6
| <code>&nbsp;&nbsp;A&nbsp;42&nbsp;</code>
| Branch if Bit Equal
| Optional special feature.
|-
| align="center" | X
| align="center" | X
| align="center" | X
| 0-7
| <code>C&nbsp;A&nbsp;421</code>
| Move and Insert Zeros
| Optional special feature.
|-
| align="center" | Y
| align="center" | Y
| align="center" | Y
| 0-8
| <code>C&nbsp;A8&nbsp;&nbsp;&nbsp;</code>
| Move Zone
| (Bits)
|-
| align="center" | Z
| align="center" | Z
| align="center" | Z
| 0-9
| <code>&nbsp;&nbsp;A8&nbsp;&nbsp;1</code>
| Move Characters and
Suppress Zeros
| &nbsp;
|-
| align="center" | 0
| align="center" | 0
| align="center" | 0
| 0
| <code>C&nbsp;&nbsp;8&nbsp;2&nbsp;</code>
| &nbsp;
| &nbsp;
|-
| align="center" | 1
| align="center" | 1
| align="center" | 1
| 1
| <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1</code>
| Read a Card
| &nbsp;
|-
| align="center" | 2
| align="center" | 2
| align="center" | 2
| 2
| <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2&nbsp;</code>
| Write a Line
| &nbsp;
|-
| align="center" | 3
| align="center" | 3
| align="center" | 3
| 3
| <code>C&nbsp;&nbsp;&nbsp;&nbsp;21</code>
| Write and Read
| &nbsp;
|-
| align="center" | 4
| align="center" | 4
| align="center" | 4
| 4
| <code>&nbsp;&nbsp;&nbsp;&nbsp;4&nbsp;&nbsp;</code>
| Punch a Card
| &nbsp;
|-
| align="center" | 5
| align="center" | 5
| align="center" | 5
| 5
| <code>C&nbsp;&nbsp;&nbsp;4&nbsp;1</code>
| Read and Punch
| &nbsp;
|-
| align="center" | 6
| align="center" | 6
| align="center" | 6
| 6
| <code>C&nbsp;&nbsp;&nbsp;42&nbsp;</code>
| Write and Punch
| &nbsp;
|-
| align="center" | 7
| align="center" | 7
| align="center" | 7
| 7
| <code>&nbsp;&nbsp;&nbsp;&nbsp;421</code>
| Write, Read, and Punch
| &nbsp;
|-
| align="center" | 8
| align="center" | 8
| align="center" | 8
| 8
| <code>&nbsp;&nbsp;&nbsp;8&nbsp;&nbsp;&nbsp;</code>
| Start Read Feed
| Optional special feature.
|-
| align="center" | 9
| align="center" | 9
| align="center" | 9
| 9
| <code>C&nbsp;&nbsp;8&nbsp;&nbsp;1</code>
| Start Punch Feed
| Optional special feature.
|-
|}

Two of the instructions, Branch on Indicator (B) and Select Stacker (K), use a "modifier" operand.

{{Col-begin}}
{{Col-break}}
 
===Modifiers for five-character Branch on Indicator (B) instruction===
The B opcode, if followed by a three-character operand, was a simple unconditional branch to the indicated address. If a fourth operand character was  present (making five characters total including the opcode), this made it a conditional branch. This "modifier" character specified the condition to be tested.

{| class="wikitable"
|-
! [[Binary-coded decimal#IBM and BCD|BCD]] Character
! Unit
! Meaning
|-
| align="center" | Blank
| 1401
| Unconditional—no word mark needed in next character
|-
| align="center" | 1
| 1009
| in run condition
|-
| &nbsp;
| 1011
| punch in backspace operation
|-
| &nbsp;
| 1011
| reader parity indicator on
|-
| &nbsp;
| 1231
| auto select
|-
| &nbsp;
| 1285
| error
|-
| &nbsp;
| 1412
| control-check indicator on
|-
| &nbsp;
| 1418
| late read
|-
| &nbsp;
| 1419
| document to be read
|-
| &nbsp;
| 1428
| late read or late reading mode change
|-
| &nbsp;
| 1445
| printer error
|-
| &nbsp;
| 7340
| hypertape unusual end
|-
| &nbsp;
| 7740
| transmission complete with abnormal status
|-
| &nbsp;
| DDC
| transmission error
|-
| align="center" | 2
| 1009
| buffer available
|-
| &nbsp;
| 1011
| punch ready
|-
| &nbsp;
| 1011
| reader ready
|-
| &nbsp;
| 1231
| full buffer
|-
| &nbsp;
| 1285
| end of line
|-
| &nbsp;
| 1412
| reader-not-ready signal on
|-
| &nbsp;
| 1418
| ready to engage
|-
| &nbsp;
| 1419
| document under read head (PDS 4)
|-
| &nbsp;
| 1428
| ready to engage
|-
| &nbsp;
| 7340
| hypertape normal end
|-
| &nbsp;
| 7740
| transmission complete successfully
|-
| &nbsp;
| DDC
| transmission ended by GMWM
|-
| align="center" | 3
| 1009
| good transmission occurred
|-
| &nbsp;
| 1011
| punch not ready to receive data
|-
| &nbsp;
| 1231
| ready to read
|-
| &nbsp;
| 1285
| reader transporting
|-
| &nbsp;
| 1412
| read-check indicator on
|-
| &nbsp;
| 1418
| document under selected read station
|-
| &nbsp;
| 1419
| valid amount field
|-
| &nbsp;
| 1428
| document under selected read station
|-
| &nbsp;
| 7340
| hypertape control unit 7641 busy
|-
| &nbsp;
| 7740
| receive request
|-
| &nbsp;
| DDC
| read request
|-
| align="center" | 4
| 1009
| reply-bad indicator on
|-
| &nbsp;
| 1011
| punch not ready to read
|-
| &nbsp;
| 1231
| empty hopper
|-
| &nbsp;
| 1285
| marked line
|-
| &nbsp;
| 1412
| amount-field indicator on
|-
| &nbsp;
| 1419
| valid process-control field
|-
| &nbsp;
| 7340
| hypertape attention
|-
| &nbsp;
| 7740
| 7740 attention
|-
| &nbsp;
| DDC
| write request
|-
| align="center" | 5
| 1009
| error reply acknowledgement
|-
| &nbsp;
| 1011
| punch overextended
|-
| &nbsp;
| 1231
| read error or overrun
|-
| &nbsp;
| 1285
| header information
|-
| &nbsp;
| 1412
| process-control indicator on
|-
| &nbsp;
| 1418
| document end
|-
| &nbsp;
| 1419
| valid account-number field
|-
| &nbsp;
| 1428
| document end
|-
| &nbsp;
| 1445
| printer busy
|-
| align="center" | 6
| 1009
| program attention required
|-
| &nbsp;
| 1011
| punch supply reel low or chad box full
|-
| &nbsp;
| 1231
| timing mark check
|-
| &nbsp;
| 1285
| ready to read a line
|-
| &nbsp;
| 1412
| account-number indicator on
|-
| &nbsp;
| 1418
| character on line
|-
| &nbsp;
| 1419
| valid transit-number field
|-
| &nbsp;
| 1428
| character on line
|-
| &nbsp;
| 1445
| carriage busy
|-
| &nbsp;
| DDC
| write in progress
|-
| align="center" | 7
| 1009
| end of message
|-
| &nbsp;
| 1285
| reader ready
|-
| &nbsp;
| 1412
| transit-number indicator on
|-
| &nbsp;
| 1418
| empty hopper and transport (end of file)
|-
| &nbsp;
| 1419
| valid serial-number field
|-
| &nbsp;
| 1428
| empty hopper and transport (end of file)
|-
| &nbsp;
| 1445
| carriage channel 9
|-
| &nbsp;
| DDC
| read in progress
|-
| align="center" | 8
| 1009
| end of file
|-
| &nbsp;
| 1285
| end of file
|-
| &nbsp;
| 1412
| document-spacing-check indicator on
|-
| &nbsp;
| 1418
| ready to read
|-
| &nbsp;
| 1419
| auto-select
|-
| &nbsp;
| 1428
| ready to read
|-
| &nbsp;
| 1448
| carriage channel 12
|-
| &nbsp;
| DDC
| system A stopped
|-
| align="center" | 9
| 1403
| carriage tape channel 9
|-
| align="center" | 0
| 1404
| validity error
|-
| align="center" | ' or @
| 1403
| carriage tape channel 12
|-
| align="center" | >
| 1448
| end of block
|-
| align="center" | /
| 1401
| unequal compare
|-
| align="center" | S
| 1401
| equal compare
|-
| align="center" | T
| 1401
| low compare
|-
| align="center" | U
| 1401
| high compare
|-
| align="center" | V
| 1301
| disk error
|-
| &nbsp;
| 1311
| disk error
|-
| &nbsp;
| 1405
| read or write parity check or read back check error
|-
| align="center" | W
| 1301
| wrong-length record
|-
| &nbsp;
| 1311
| wrong-length record
|-
| &nbsp;
| 1405
| wrong-length record
|-
| align="center" | X
| 1301
| unequal address compare
|-
| &nbsp;
| 1311
| unequal address compare
|-
| &nbsp;
| 1405
| unequal address compare
|-
| align="center" | Y
| 1301
| any disk-unit error condition
|-
| &nbsp;
| 1311
| any disk-unit error condition
|-
| &nbsp;
| 1405
| any disk-unit error condition
|-
| align="center" | Z
| 1401
| arithmetic overflow
|-
| align="center" | ‡
| 1403
| printer error (record mark)
|-
| align="center" | ( or %
| 1401
| process check with process check switch off
|-
| &nbsp;
| 1440
| I/O check stop switch off
|-
| align="center" | \
| 1301
| access busy
|-
| &nbsp;
| 1311
| access busy
|-
| align="center" | J
| 1419
| I/O channel-busy indicator
|-
| &nbsp;
| TAU
| tape busy
|-
| &nbsp;
| SIO
| serial input-output busy
|-
| align="center" | K
| TAU
| end of reel (writing) or tape mark (reading)
|-
| align="center" | L
| TAU
| tape error
|-
| align="center" | N
| 1301
| access inoperable
|-
| &nbsp;
| 1311
| access inoperable
|-
| &nbsp;
| 1405
| access inoperable
|-
| align="center" | P
| 1403
| printer busy
|-
| align="center" | Q
| 1407
| inquiry request
|-
| align="center" | R
| 1403
| carriage busy
|-
| align="center" | !
| 1402
| punch error
|-
| align="center" | *
| 1407
| inquiry clear
|-
| align="center" | + or &
| 1442
| last card (Reader unit 2)
|-
| align="center" | A
| 1402
| last card if SS A is on
|-
| align="center" | B
| 1401
| SS B
|-
| &nbsp;
| 7340
| hypertape attention response
|-
| align="center" | C
| 1401
| SS C
|-
| align="center" | D
| 1401
| SS D
|-
| align="center" | E
| 1401
| SS E
|-
| &nbsp;
| 7340
| hypertape end response
|-
| align="center" | F
| 1401
| SS F
|-
| align="center" | G
| 1401
| SS G
|-
| align="center" | H
| 1402
| reader busy
|-
| align="center" | I
| 1402
| punch busy
|-
| align="center" | ?
| 1402
| reader error
|-
| align="center" | <
| 1448
| early warning
|-
|}

{{Col-break}}

===Modifiers for Select Stacker (K) instruction===
The Select Stacker (K) instruction sent commands to various devices. It was named for its relevance to the 1402 reader/punch.

{| class="wikitable"
|-
! [[Binary-coded decimal#IBM and BCD|BCD]] Character
! Unit
! Meaning
|-
| align="center" | Blank
| 1401
| set program activity recording at BBB only if A is, dd
|-
| align="center" | 1
| 1402
| select last card read to stacker 1 if within 10 ms
|-
| align="center" | 2
| 1402
| select last card read to stacker 8/2 if within 10 ms
|-
| align="center" | 4
| 1402
| select previous card punched to stacker 4
|-
| align="center" | 8
| 1402
| select previous card punched to stacker 8/2
|-
| align="center" | = or #
| 1444
| select previous card punched to stacker 2
|-
| align="center" | L
| 1009
| operate in load mode
|-
| align="center" | $
| 1402
| overlap on
|-
| align="center" | A
| 1009
| suppress 3-second alarm
|-
| align="center" | C
| DDC
| read request
|-
| align="center" | D
| 1009
| set direction to receive
|-
| &nbsp;
| DDC
| write request
|-
| align="center" | E
| 1009
| set direction to transmit
|-
| &nbsp;
| DDC
| reset
|-
| align="center" | F
| 1009
| send EOF
|-
| align="center" | .
| 1402
| overlap off
|-
| align="center" | )
| 1402
| reset overlap
|-
|}
{{col-end}}

{{hidden end}}

==1401 culture==
<!-- {{Original research|section|date=April 2009}}   Deleted texts without citations 2013.12 -->

<!-- == Art inspired by the 1401 ==  art qualifies as culture, does not need a separate heading -->
In October 2006, [[Iceland]]ic avant-garde musician [[Jóhann Jóhannsson]] released the album ''[[IBM 1401, A User's Manual]]'' through music publisher [[4AD]].<!--Host is up but this page is down: <ref>{{cite web |title= Jóhann Jóhannsson profile |work= 4AD web site |url= http://www.4ad.com/johannjohannsson/profile |title=ibm 1401, a user´s manual |access-date= June 2, 2010 }}</ref>--><ref>{{cite web |url=http://www.ernaomarsdottir.com/index.php?/othershows/ibm-1401-a-users-manual/ |title=IBM 1401, A User's Manual-Live in Italy |access-date=January 29, 2015}}</ref> The concept is based upon work done in 1964 by his father, Jóhann Gunnarsson, chief maintenance engineer of one of the country's first computers, and [[Elias Davidsson|Elías Daviðsson]],<ref name="Elias">{{cite web |url=http://www.ausersmanual.org/credits/ |title=Jóhann Jóhannsson: IBM 1401, A User's Manual |work=work's web site |access-date=January 29, 2015 |archive-url=https://web.archive.org/web/20150211064627/http://www.ausersmanual.org/credits/ |archive-date=February 11, 2015 |url-status=dead }}</ref> one of the first programmers in the country. The album was originally written for a string quartet, organ and electronics and to accompany a dance piece by long-standing collaborator friend, Erna Ómarsdóttir. For the album recording, Jóhann has rewritten it for a sixty-piece string orchestra, adding a new final movement and incorporating electronics and vintage reel-to-reel recordings of a singing 1401 found in his father's attic.<ref name="Elias"/>

More well-known are various demo programs to play music on transistor radios placed on the CPU<ref>{{cite web | title = 1401-music-Movie | website=[[YouTube]] | date=December 18, 2008 | url = https://www.youtube.com/watch?v=myt6DApmiv0 }}</ref> and computer "art", mostly [[kitsch]]y pictures printed using Xs and 0s on chain printers.<ref>{{Cite web |last= Gansing |first= Kristoffer |title= Working Paper version - Humans Thinking Like Machines - Incidental Media Art in the Swedish Welfare State |publisher= University of Malmö, School of Arts & Communication |year= 2007 |url= http://dspace.mah.se:8080/bitstream/handle/2043/7221/gansing_replace.pdf?sequence=1 |access-date= 29 November 2017 |archive-date= March 23, 2012 |archive-url= https://web.archive.org/web/20120323154737/http://dspace.mah.se:8080/bitstream/handle/2043/7221/gansing_replace.pdf?sequence=1 |url-status= dead }}  A full version to be published in ''Place Studies in Art, Media, Science and Technology'', VDG Weimar 2009</ref>
Other programs would generate music by having the printer print particular groups/sequences of characters using the impact of the printer hammers to generate tones.

An IBM 1401 was the first computer introduced in [[Nepal]] for the census purpose in 1971. It took about one year to take the census of the country. At that time the population of Nepal was about 10,000,000.

==Truck-based portable version==
A truck-based IBM 1401 configured in 1960 for military use was designated a ''portable'' computer, and nicknamed a DataMobile.<ref>[https://web.archive.org/web/20120403025431/http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/mainframe/impacts/ IBM 1401: The Mainframe] --Cultural impacts</ref><ref>[https://web.archive.org/web/20120403020416/http://www-03.ibm.com/ibm/history/ibm100/us/en/icons/mainframe/ IBM 1401: The Mainframe]-- Overview</ref><ref>[http://www.columbia.edu/cu/computinghistory/1401.html Columbia University Computing History]--The IBM 1401</ref>

==See also==
* [[IBM 1400 series]]
* [[Honeywell 200]]
* [[Bull Gamma 10]]

==Notes==
{{Notelist}}

==References==
{{Reflist}}

==Videos==
* [https://www.youtube.com/watch?v=FVsX7aHNENo ''IBM 1401 System - 50th Anniversary in the Computer History Museum''] YouTube November 19, 2009
* [https://www.youtube.com/watch?v=xUQnVt5qS-Y ''IBM 1401 French Presentation with English Subtitles''] YouTube April 20, 2014
* [https://www.youtube.com/watch?v=SOe6MHYtc3g&t=8s ''IBM 1401 for the Roper Corporation''] YouTube May 14, 2015
* [https://www.youtube.com/watch?v=uFQ3sajIdaM ''The IBM 1401 compiles and runs FORTRAN II''] YouTube February 2, 2018

==Further reading==
* {{cite book |title=IBM's Early Computers |last=Bashe |first=Charles J. |author2=Johnson, Lyle R |author3=Palmer, John H. |author4=Pugh, Emerson W. |year=1986 |publisher=MIT |isbn=0-262-02225-7 |pages=[https://archive.org/details/ibmsearlycompute00bash/page/717 717] |url-access=registration |url=https://archive.org/details/ibmsearlycompute00bash/page/717 }} Chapter 12 ''Broadening the Base'' pages 465–494, a history of IBM's 1401 and 1403 development
* {{cite book   |publisher=IBM 
   |title=IBM 1401 System Summary  |id=A24-1401-1  |date=April 1966
   |url=http://bitsavers.trailing-edge.com/pdf/ibm/1401/A24-1401-1_1401_System_Summary_Sep64.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://bitsavers.trailing-edge.com/pdf/ibm/1401/A24-1401-1_1401_System_Summary_Sep64.pdf |archive-date=2022-10-10 |url-status=live
   }} ''Brief descriptions of the machine features, components, configurations, and special features''
* {{cite book   |publisher=IBM 
   |title=IBM 1401 Data Processing System: Reference Manual   |id=A24-1403-5   |date=April 1962
   |url=http://bitsavers.org/pdf/ibm/140x/A24-1403-5_1401_Reference_Apr62.pdf
   |url-status=dead
   |archive-url=https://web.archive.org/web/20100809033646/http://www.bitsavers.org/pdf/ibm/140x/A24-1403-5_1401_Reference_Apr62.pdf
   |archive-date=August 9, 2010   |df=mdy-all}}

==External links==
* [http://www.bitsavers.org/pdf/ibm/1401/ 1401 documents on bitsavers.org]
* {{cite video
 |date=November 16, 2009   
 |title=A Century of Smart: The IBM 1401 (1959)
 |url=https://www.youtube.com/watch?v=hQcaYvbwLPo
 | archive-url=https://web.archive.org/web/20110309142628/http://www.youtube.com/watch?v=hQcaYvbwLPo| archive-date=2011-03-09 | url-status=dead|publisher=IBM Social Media   |access-date=November 17, 2009}} Video captures thoughts and reflections of some of the original 1401 team members from a reunion held in Endicott, NY in 2009. Includes footage from 1401 marketing films.
* [http://ibm-1401.info/Movies-n-Sounds.html 1401 videos and sounds]
* [http://www.multicians.org/thvv/1401s.html 1401s I have Known], [[Tom Van Vleck]]
* {{cite journal
 |journal      = IBM Systems Journal
 |volume       = 4
 |issue        = 1
 |year         = 1965
 |pages        = 73–80
 |author       = L. H. Haines
 |title        = Serial compilation and the 1401 FORTRAN compiler
 |url          = http://domino.research.ibm.com/tchjr/journalindex.nsf/495f80c9d0f539778525681e00724804/cde711e5ad6786e485256bfa00685a03?OpenDocument
 |doi          = 10.1147/sj.41.0073
 |access-date  = September 30, 2008
 |archive-date = February 14, 2012
 |archive-url  = https://web.archive.org/web/20120214031508/http://domino.research.ibm.com/tchjr/journalindex.nsf/495f80c9d0f539778525681e00724804/cde711e5ad6786e485256bfa00685a03?OpenDocument
 |url-status   = dead
|url-access= subscription
 }} This article was reprinted, edited, in both editions of {{cite book | first = John A. N. | last = Lee | title = Anatomy of a Compiler | publisher = Van Nostrand Reinhold | date = 1967 |edition= 1st and 1974 2nd}}
* Music inspired by the 1401: Johann Johannsson's "IBM 1401: A User's Manual" - [http://www.4ad.com/releases/385 CD] / [http://www.4ad.com/releases/862 LP]
* [http://files.righto.com/sms/ADB.html a double width SMS card used in the 1401] used germanium alloy transistors
* {{cite web |first=Ken |last=Shirriff |title=Booting the IBM 1401: How a 1959 punch-card computer loads a program |url=http://www.righto.com/2021/02/an-ibm-1401-mainframe-computer-at.html |date=February 2021}}
* {{cite web |first=Ken |last=Shirriff |title=Germanium transistors: logic circuits in the IBM 1401 computer |date=March 2021 |url=http://www.righto.com/2021/03/germanium-transistors-logic-circuits-in.html}}
* Jaeger, Jay (GitHub) [https://github.com/cube1us/IBM1410FPGA IBM1410FPGA (VHDL)] [https://github.com/cube1us/IBM1410Console IBM1410Console (C#)]

{{IBM midrange computers}}
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{{DEFAULTSORT:Ibm 1401}}
[[Category:IBM 1400 series|1401]]
[[Category:Computer-related introductions in 1959]]
[[Category:Magnetic-core memory computers]]
[[Category:Variable word length computers]]
[[Category:Decimal computers]]