Talk:IBM 1401

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Introduction from RTC
Edward G. Nilges 3-25-2005 spinoza1111@yahoo.com: I have added information to this excellent article on 1401 software, notable installations, and in summary as to its human impact based on sources and personal experience. Let me know what you think, oh Collective.


 * Keep right on going with anything you have. Please register a user name, so we can get to know you. -- RTC 00:23, 25 Mar 2005 (UTC)

I have registered with spinoza1111 and all contributions should appear under this userid.

IBM 1401: fixed I/O memory
From memory (of IBM UK Education Dept, 1961 - 64) the reason op codes 1 - 7 incl. did not need an address was that cards were always read into memory locations 1-80 and were punched from locations 101 - 180, and the line printer printed from locations 201 - 332 (printer line width was fixed at 132 characters). This led to the most noisy instruction being the single op code 7   which read a card, punched a card and printed a line.

I also remember the difference between group marks and word marks, but not how they were coded. A word mark identified the op code. A group mark might have been relevant only with tape I/O, but my memory is not clear on this. Was the character size increased by 1 bit to incorporate the word mark?

Van.snyder (talk) 01:07, 3 April 2011 (UTC) Word mark is an extra bit in each character. Group mark is BA8421. Group mark with word mark stops transmission, either on tape or any other I/O that's not unit record (cards or printer). On the 1440, even unit-record I/O is character serial, so GMWM stops all I/O transfers.

I also have a good memory of SPS, the assembler programming language, and recall writing the manual on the "Sterling Hardware Feature", almost universally installed in the UK, This used the Move Characters and Edit instruction, which was incorporated into the design to allow users of non-decimal currencies and weights and measures to write commercial programmes simply.

David Collins

dscollins@dsl.pipex.com

In the early 1970s, Computer Technology Inc. had a data center in Arlington, TX, that included several large System/360 computers, along with a S/360 Model 30 connected to one of the large machines through a channel as a peripheral device, solely to use its 1401 Emulator. Tom O'Brien

Software
paragraph: "Major software on the 1401 included a simple assembler called the Symbolic Programming System (SPS) and a more advanced form of assembler, Autocoder. The only high-level language in common use was the RPG (Report Program Generator) language, a declarative language primarily for specifying accounting reports still in use on IBM's midrange AS/400."

Actually, a language called FARGO (Fourteen-o-one Automatic Report Generation Operation) was the predecessor of RPG. --YORD-the-unknown 15:50, 19 July 2006 (UTC)

The 1.4K, 2K, and 4K machines could not compile programs ...
The 1.4K, 2K, and 4K machines could not compile programs, and had to be supplied with programs compiled on a more expensive machine. Assuming that "compile" as used here includes "assemble", I deleted this text and added some storage requiremnents to the later text about software. 69.106.254.246 17:42, 17 September 2006 (UTC)


 * Good, I always felt that needed clarification. However I didn't have any details myself. -- RTC 20:16, 17 September 2006 (UTC)

Thanks for cleaning up the wording; knew that I hadn't done the complete job; my style seems to be collect first, polish later. The details are all from online manuals via one of the external links, not the kind of stuff I would trust memory for. btw, I seem to see your tracks wherever I go. 69.106.254.246 23:07, 17 September 2006 (UTC)

The CADET Name

Internally, the 1401 mainframe was unusual, because it did not use adders -- principally because BCD adder circuits are more complex than binary adders. The 1401 therefore performed addition (and other arithmetic operations) by Table Lookup. In other words, to add (say) 7 and 9, the machine went to a table and looked up the intersection of 7 and 9, finding the answer 16, and brought that back to the data being processed. And so, for larger numbers, where elements were added, e.g., 14 + 32 was processed by looking up the sum of 4 + 2, then the sum of 1 + 3 (multiplying the answer by 10), then adding the results. Seems cumbersome, but less so than a full BCD adder.

For marketing purposes, the 1401 System was called the CADET. Because of the unusual arithmetic processing design, the machine was known among IBM engineers on the project as Can't Add, Doesn't Even Try.

The 1401 was never known as "CADET." That was the 1620, which never had arithmetic circuits. Arithmetic was done by table lookup. We used this to write programs that worked in octal instead of decimal, for telemetry processing. Van.snyder (talk) 01:03, 3 April 2011 (UTC)

1402 Reliability Check

The 1402 Card Reader-Punch was innovative in that it read card holes optically, not by brushes as in earlier card readers. In previous machines, a row of 80 brushes was provided, one brush per column. Punched cards would pass under the brushes, so when there was an open hole the brush tip would make contact with the underlying metal surface, completing a circuit and creating an electrical pulse. Because the pulse timing corresponded with the position of the on-the-fly card, the row was identified in the corresponding column. This system worked fairly well with low-speed card movement, but at higher speeds the brushes sometimes would not make contact; and in any case, the signals were not "clean", i.e., staticky. (By the way, that is why IBM cards had rectangular holes, rather than round holes which were of course easier to make.)

Optical hole readers allowed an order of magnitude (or more) greater speed in reading cards. This was very important, as reading data (or instructions) from cards was the limiting factor in how fast the machines could process data. Reading cards electronically, rather than electrically, helped move data input speeds closer to the processing speeds of the machine's electronics. That is why 1401 systems were often used as the data I/O interfaces for larger systems, such as the 700 and 7000 series machines.

The optical system featured a row of 80 photocells, positioned below an illuminating light, with the card passing between them. When the card had a hole, the photocell would be energized, and the signal would indicate that the card was puinched in that position. However, there was great concern that if one of the photocells (or the illuminating light above them) would fail, then the data input would be erroneous -- and possibly many cards, perhaps thousands, would be read incorrectly.

I was the engineer who designed circuitry such that all 80 photocells were checked before the card arrived at the read station (all ON), then checked again between the card edge and the first row (all OFF), then checked again between each row (all OFF), then checked after the final row (all OFF), then checked again after the trailing edge of the card passed (all ON) but before arrival of the subsequent card.

With this system, any photocell (or light source) which failed would be detected immediately. The machine would be brought to an immediate stop, so that the failure could be repaired and the operation re-started with the card in process when the failure occurred. In this manner, the reader could be operated as fast as the cards could be pushed through, without encountering problems of vibration, tearing, folding, etc.

On The Topic of Punched Cards

One might wonder why IBM punch cards were made in the size that was chosen. Certainly they could have been much smaller, still with plenty of space for 80 columns and 14 rows. In fact, competitors did utilize much smaller cards in their equipment.

IBM chose its card size to be identical with the size of US currency, in the 1920s and earlier, prior to its being changed during the Great Depression. That was so customers could store their punched cards in the drawers of cash registers, and other containers for currency. Thus small merchants could record their sales, inventory, and payroll data on cards, store them in available compartments, and not risk having the cards slide around into a jumbled mass or even perhaps slide our of sequence. This actually was a big selling point for the IBM sales force.

Because of these oversized cards, IBM became the largest purchaser of the particular cardboard stock, which was used by all manufacturers who made punched-card equipment. Wehn the US Government changed the size of currency, IBM retained the original card size because there was so much equipment in existence using the original card size. Changing card size would have meant either replacing all of the equipment in being (much of which was being rented to customers by IBM), or else requiring customers to have two sizes of data processing equipment. So the original card size persists to the present day -- though of course, punched cards are little used presently for data storage.

The use of punched cards became so vast, that the sale of (blank) cards became one of IBM's main revenue sources, and one of its most profitable businesses.

Comments from Kent L. Aldershof; Aldershof-MSII@Prodigy.net —Preceding unsigned comment added by 70.111.225.17 (talk) 20:32, 27 November 2010 (UTC)


 * Thanks for the interesting comments. What competitor had smaller cards? Remington Rand had more data (90 characters) on its cards, but they were the same size. I suspect the card size was appropriate in the electromechanical era, the rectangular holes produced nice clean pulses to relays when brushes made contact through them as the cards passed through the read station. Making all the mechanical equipment much smaller was probably not feasible in the 1920s and 30s. IBM introduced a much smaller format with the System/3, but that was late in the game and didn't last long. Also, I heard the CADET story about the IBM 1620, which used a lookup table for addition. The 1401 did have an add instruction, op code A.--agr (talk) 20:46, 28 November 2010 (UTC)

1402 LOAD button
I like completeness and left to myself, will add all kinds of stuff. But I think details of the 1402 LOAD button do not belong in the article. Memory, Addressing, Instructions are necessary to understand the 1401. The function of the LOAD button is a operational nit. Can we delete it?

I'd also delete the existing text about errors, just more operational nits. 69.106.254.246 07:56, 18 September 2006 (UTC)


 * I think bootstrapping is an interesting and usually quirky aspect of any computer. So I think the details of the LOAD button and typical first-few-instructions discussion should stay. Jeh (talk) 10:50, 3 July 2012 (UTC)

Character and Op codes table is wrong
The BCD column includes "C", for check bit I assume, but the checkbit also includes any wordmark and so cannot be determined just from the 6 bit character.69.106.254.246 08:14, 18 September 2006 (UTC)


 * You are correct. Nevertheless, that's what's in the IBM manuals. Jeh (talk) 14:33, 17 March 2010 (UTC)

Announced as marginal...
Announced as marginal, and for the simple accounting of midrange companies and as a sort of slave print server to the IBM 7090, the 1401 (like many other platforms before it and since) attracted its own hard core of devoted followers, who could see that although marketed as limited in function, the 1401 was in logical terms a real computer, whose secrets could be unlocked by people sufficiently patient to understand its arcane addressing scheme, and to devise ways around its limitations.

I was there, programming 1401's for the US Army, IBM, ... from 1959 to about 1967 and disagree with almost everything in that sentence. So I am a "hard core ... devoted follower", but am I wrong? Did IBM really sell 20,000 marginal machines? 69.106.254.246 06:01, 18 September 2006 (UTC)

Found IBM announcemet day material. Inserted some text from that and deleted the "marginal" paragraph as unsupported!69.106.254.246 20:16, 18 September 2006 (UTC)

An optional "Advanced Programming Option" allowed for additional flags for 3 bytes within the first 100.
I used to program the 1401 - lots - and I have no idea what that sentence means.69.106.254.246 05:41, 18 September 2006 (UTC)

Funny - I was just going to say the same thing! It may have something to do with the optional index registers... I suggest we delete this sentence unless someone clarifies it.Jpaulm (talk) 14:22, 3 November 2008 (UTC)


 * Deleted. Only took 18 months. :) The index register scheme is covered in the next graf. Jeh (talk) 18:24, 18 May 2010 (UTC)

Deleted "...1969 ... Red concertgoers"
"An IBM 1401 installation located on Michigan Avenue and Congress Parkway was attacked in 1969 by Red concertgoers to a Sly and the Family Stone concert but the crowd did little damage.-ref-Chicago Tribune, 2 August 1970, Page A1-/ref-"

As best I can find the concert was July 27, 1970 (not 1969 - note the Tribune 1970 date) and the concertgoers were disappointed at the no-show Sly & Family. If they were "Red" (with a capital "R"!) it would have been because of summer weather in Chicago. Too many mistakes, too little contribution - deleted. 69.106.237.145 (talk) 08:32, 19 April 2011 (UTC)

Link to Bit slicing deleted
I deleted it because I don't think it applies. A bit-slice microprocessor, as the term is normally used, is a complete MPU and can be used as such in its own native bit width; or it can be combined with others to implement wider MPUs. The fact that IBM implemented one bit of, say, a BCD adder on a card and then used multiple cards to handle the entire BCD digit isn't really the same thing. Those cards were never intended to be used independently, nor could you have combined eight of them instead of four to implement a wider-bit-width adder. Anyway, a tremendous number of discrete transistor machines, to say nothing of tube machines, did something similar with a card or module implementing some basic function for a single bit. If this means the 1401 is a bit-sliced implementation, then so are they all, and the term loses most of its meaning. I'll leave the references to the 1401 on the Bit slicing page alone pending consensus here. Jeh (talk) 18:33, 29 April 2011 (UTC)


 * I'll "consent" either way, it's out of my field -- just so that both articles agree. (it's nice to know someone is reading this) 69.106.237.145 (talk) 21:48, 29 April 2011 (UTC)

1401 memory
There is reference in the article to the hardware of the logic circuitry but none to the hardware of the memory. I was a programmer fifty years ago and not an engineer but on the odd occasion when the back was off the machine I'd have a look at the chunks of electronics. The memory comprised copper cores (very small and torus shaped) - I kept a few in my desk drawer - I wish I still had them! Anyway the cores were arranged in arrays and had three wires at right angles passing through each. Quite how they worked I don't know, but clearly the wires had to do with setting the bits on or off and detecting whether they were on or off. And of course that is why main memory of a computer was called core storage. It was the standard of the day and I'm not suggesting that the 1401 was special, or even the first, but I think some reference to the memory hardware is called for. I have inadequate knowledge, reference works and literary skill to write it. Tom1942 19:26, 2 July 2012 (UTC)


 * They're ferrite, not copper... though they may have been copper-colored (more likely rust-colored). How core memory works is well described in the Magnetic-core memory article. Jeh (talk) 20:36, 2 July 2012 (UTC)

Agreed, I don't know why I said copper, which doesn't, of course, have the necessary magnetic properties to do the job. However my primary and quite simple point is that there should be spme reference in this article to the hardware of the 1401's main memory. I'd expect it to be quite brief but to contain references to other articles eg as mentioned by Jeh for those who want to pursue it. Tom1942 — Preceding unsigned comment added by Tom Beaton (talk • contribs) 14:57, 11 July 2012 (UTC)


 * Well, I added a sentence, with a beg for more info (how many bits per plane, size of the cores, cycle time, was it three- or four-wire?, etc.) in the edit summary. To do more we'd need a reference. Maybe one of the people working on the 1401 restoration project at the Computer Museum in the SF Bay area can point to the right IBM manual. It might even have been scanned and placed online... I feel this machine does deserve significant coverage here, as IBM sold or leased a great many of them and afaik they were the last widely used decimal-based computer. Jeh (talk) 22:02, 15 July 2012 (UTC)


 * I found some references and added some details. Might be able to find more, but this is a good start. Jeh (talk) 23:44, 15 July 2012 (UTC)

More on the C bit
This text is necessary  Note: If Word mark bit is set, then the C bit will be opposite of shown.

This text is useless:


 * Of course, the C bit was determined and checked automatically by the machine - normally it was of no concern to the programmers. The only way the C bit could be entered was by manually using the switches on the Auxiliary Console. A programmer might use these switches to make quick patches while debugging.

1) Programmers never entered a C-bit, they entered all the bits of a memory location; the C-bit is not deserving of special mention in that context. 2) That an auxiliary (maintenance) console allowed making changes to memory locations is true of most, if not all, large  (as opposed to personal) computers, is not special to the 1401, and contributes nothing to the reader's understanding of the 1401.99.65.176.161 (talk) 21:30, 7 December 2013 (UTC)


 * Maybe it's useless to you; I don't think you're entitled to make that evaluation on behalf of all readers.


 * It is true that programmers never enter (or read) the C bit. However, all references I'm aware of for the 1401, including IBM's manuals (of which I still have two), describe memory locations as having eight bits: C, B, A, 8, 4, 2, 1, and M. We describe the word mark bit's role as a field delimiter. I feel the explanation of the C bit is similarly necessary to make clear that only six bits are really available for data storage, especially given that the character code table (again, from the references) includes the C bits. Also, parity bits don't exist in most modern computers below the server class, and so many readers may not be familiar with them. Even other computers of the same or slightly later era (such as System/360) did not discuss the parity check bit so prominently.


 * Regarding the auxiliary console, it is true that such consoles were common to computers of that era, but that does not mean it should not be described in this article. I would agree that this discussion of the C bit may be the wrong place for it. But it is to me quite interesting that the aux. console switches permit writing memory with an incorrect parity bit! It is true that that information is "useless", to the vast majority of readers, in that they'll never encounter a 1401, let alone have a reason to use the aux console. That doesn't mean it isn't interesting. If anything it demonstrates the low level nature of the operations possible via the aux console. And in that way it does contribute to the reader's understanding. Jeh (talk) 21:59, 7 December 2013 (UTC)

IBM 1401 motivation
The stable version of the lede said


 * "it was aimed at replacing electromechanical unit record equipment for processing data stored on punched cards."

With this edit, IP 99.65.176.161 removed the word "electromechanical", with edit comment


 * delete "electromechanical". 1401 was aimed at 407 and the electronic 604 - see Bashe IBM's Early Computers ch.12

This is a mysterious statement as the 407 and all other unit record equipment (card sorters, collators, reproducing punches, etc.) except the 604 were electromechanical. The 604 included a large electronic component, but it was sold as the "604 Calculating Punch", with that enclosure attached to a modified 519. Thus the 604 gave you a "high speed" arithmetic unit that could be used as an add-on accessory to other unit record (or "tabulating card" or simply "tabulating") equipment. This did not in any way make the tab card equipment not electromechanical. Nor was a 604 (or equivalent) a required component of such a shop; a lot of them got along without one.

So, I restored the word "electromechanical".

99. responded with this edit, changing the wording to


 * its development had begun in 1954 as IBM's response to the Bull Gamma 3 electronic calculator. ref: Bashe (1986) p.461.

Sorry, but Bashe (Bashe, Johnson, Palmer, and Pugh: IBM's Early Computers, 1986, MIT Press) does not say anything like that. It would be charity to even call this a misinterpretation of the book. The only way to support such a conclusion would be to notice the mention of the Bull Gamma 3 (and IBM's initial reaction) on page 461, notice that the 1401 development is described  later in the chapter... and ignore most of the material in between.

If you actually read that material, the picture is very different. First, yes, it is indeed noted that the Bull Gamma 3 presented competition to the IBM 604 (a "calculating punch", a device used in a unit record shop where more-complicated math was required). As described on page 462-463, IBM's response to that competition was the "MAC program," and on page 464, it is noted that "of the machines considered part of the MAC series, only the 608 calculator was produced." (i.e. no computers.) The next shipping product mentioned (page 465) was the IBM 7070 Data Processing System, which "bore little resemblance to the planned 750" (which was part of the MAC series) and furthermore "failed to leave a lasting imprint on the product line."

Thus the MAC projects that were IBM's direct response to the Bull Gamma 3 did not culminate in the 1401, but rather in a dead end.

Then we have the top of page 469, which cites IBM's Francis Underwood: "What was wanted ... was a machine capable of replacing three 407's at... rental of $2500 per month, including card reader, punch, printer, and processor." (Note, no mention of replacing a 604!) This introduces the section describing the 1401 development.

There is also the quote at the beginning of the history section here, from the IBM 1401 product announcement:


 * "The all-transistorized IBM 1401 Data Processing System places the features found in electronic data processing systems at the disposal of smaller businesses, previously limited to the use of conventional punched card equipment."

These quotes sound exactly like "replacing unit-record equipment" to me, and not at all like "response to the Bull Gamma 3 electronic calculator."

I would also add the observation that if you're just competing with a faster, cheaper competitor to the 604, you don't need tape drives or an RPG compiler ("developed by IBM in 1959 as ... a tool to replicate punched card processing on the IBM 1401"). RPG was specifically designed to make it easy to take accounting processes that had been implemented on unit record equipment and re-implement them in code. Sure, if a 604 had been part of your setup RPG could handle that part of the workflow too... but I will note again that 1401's replaced a lot of unit record equipment collections that did not include a 604... so the claim that the 1401 was developed in response to a 604 competitor is very specious. The claim that it was developed to replace unit-record equipment, on the other hand, is well supported. Jeh (talk) 08:37, 26 June 2014 (UTC)


 * I tend to agree. The 604 was introduced in 1948, eleven years before the 1401. An enormous amount happened in this 11 years. IBM went through generations of computers, the one-offs, like the Mark I and NORC, the Williams tube 701, the core memory FSQ-7, the 704/709 series, the 702/705, the relatively high volume 650. If there is any substance to the Bull Gamma 3 story, it may belong in the history section, but not the lede. I'm also inclined to put back the modifier table. It provides some texture about how the machine evolved.--agr (talk) 01:50, 27 June 2014 (UTC)


 * I can't find any support at all for the notion that the 1401 was a response to the Bull Gamma 3. It's just a coincidence of timing. Re the modifier table, I also agree regarding "texture" (good word for it). It's not as if the table is particularly large compared to the character set/opcode table. Jeh (talk) 05:34, 27 June 2014 (UTC)


 * The IP has not responded in about 36 hours, so... ✅

Bytes?
Thanks, you are probably right? Technically I was too? Or at least going by sources (that I didn't add, sorry..). Yes, didn't find "The 1401 was equipped with up to 4K 8-bit characters of core memory" in a IBM reference (and maybe that source is just wrong). Looking more closely I see "The 1401 was a decimal (not binary) computer, with variable-length words composed of 8-bit bytes containing 6-bit BCD (binary coded decimal) characters (plus parity and wordmark bits)". I'm not even sure what they mean by "wordmark".. but if parity was for hardware reliability then yes, maybe not fair to count as "8-bit" (7-bit?) similar to that we do not count ECC bits.

Byte doesn't strictly have to mean 8-bit.. :) Thought of using "kwords" but this machine is variable word sized.. not familiar with it or what that would mean then..

This is kind of important as I had just done this and I'm just curious.. It was our first computer (and the first in the country) and I could ask some old colleges but they probably didn't know the computer at this low level (and it would be OR..). Parity is at least also a "software concept", not sure you could hack the machine to work as (an unreliable?) 8-bit one? Maybe I could rely on to know..? comp.arch (talk) 17:09, 29 January 2015 (UTC)


 * I have one of the IBM programming manuals for the 1401. It too says eight bits per position: "The capacity .. is 1400, 2000, ... or 16000 alphanumeric characters of 8-bit core storage...". However it is incorrect to call them bytes, because the 8 bits are not equivalent to the 8 bits we have in a modern byte machine.


 * The "word mark" bit is a delimiter for the variable-length fields. You could think of it as being a little like a tab stop on a typewriter. A character position with bits 2 and 4 set represents a "6" numerically (and textually too, no need to convert from text to numeric data or back on this machine!) whether the word mark bit is set or not. The word mark is set in the character position that held the most significant digit of a multi-digit number. Word mark bits also marked the "left position" (lowest address) of a text field for Move and similar instructions.


 * No, it would not be possible to use the parity bit for arbitrary data (any more than you can store 9 bits x 256M of arbitrary data in a 256Mx72 ECC DIMM). If the 1401 ever reads a character with an invalid parity bit, it halts with an error indication. Come to think of it, the 1401 makes it pretty damn difficult to access even the data bits of those characters: There are no bitwise instructions (not, and, or, shift, etc.). For digits you could do integer arithmetic on them and tease out the bits. But it's not clear to me what would happen if you tried to do that to, say, the letter "A".


 * So... we have six-bit characters. (Note that there are 64 entries in the character code chart, and these represent every possible combination of the six data bits.) Associated with each character is a word mark bit and a parity bit. It is true that there are eight bits per character position but the extra two bits are not ordinary data bits.


 * It is true that "byte" has been used here and there to mean other than 8 bits. However I think that only a small fraction of readers will not immediately assume that "byte" means "8 bits". So if we call them "bytes" then we're going to have to explain that no, they're not really "eight-bit bytes" in this machine. That explanation will have to be in a few different places, because many readers don't read articles linearly. And even then, many readers will ignore the explanation and get the wrong message. By calling them "characters", we immediately alert the reader that this is something different. We also follow the terminology that's in IBM's own documentation for the machine.


 * I feel strongly that similar considerations should apply to articles on other machines that didn't use 8-bit bytes. For example, the CDC 36- and 60-bit machines were sold in terms of a number of words (e.g. "32K 36-bit words"). These machines commonly used 6-bit characters (although various libraries supported the use of larger character sets). Now, we could do the arithmetic and say that in "32K 36-bit words" there are actually 288 Kbytes (8-bit bytes) of memory, but that's misleading, because the machine doesn't have any opcodes to access 8-bit portions of a word. And we shouldn't call them "6-bit bytes" because it would violate the "principle of least astonishment". "Characters" is what those machines' makers generally called 6-bit things, and we should too. Jeh (talk) 18:28, 29 January 2015 (UTC)

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Videos proposition

 * The IBM 1401 compiles and runs FORTRAN II YouTube February 2, 2018 — Preceding unsigned comment added by 89.25.210.104 (talk) 00:31, 16 February 2018 (UTC)

Info box
The info box needs to be for a computer, not just the CPU. Bubba73 You talkin' to me? 18:30, 18 July 2019 (UTC)
 * There is Template:Infobox computer hardware, but it's not ideal. Maybe we need an info box for historic computers.--agr (talk) 18:53, 18 July 2019 (UTC)