In 1959, Donald Knuth wrote an assembly program named SuperSoap for the IBM 650. Here is the manual, and here is a listing of the program (in SuperSoap assembly language). Quoting from the abstract:

SuperSoap is a major revision of Case SOAP III [Knuth's modifications to SOAP II], designed to take advantage of a 650 with extra attachments. The present SuperSoap program requires index registers, core, a disk file unit, and the table-lookup-on-equal feature.

Note the bolded text. Looking at the available documentation on Bitsavers, we know that the index registers and core come with the IBM 653, and the disk file unit is presumably an IBM 355. But what is this mysterious "TLE"? Appendix I of the SuperSoap manual lists operation codes and mnemonics, assigning TLE to operation code 63. Available 650 documentation that lists instructions says that operation code 63 is unused. It does not seem to have been added when the Model 4 was released (see the last section, beginning on page 33, of this document).

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    Guess: Sometimes institutions (e.g. universities) had custom-made extensions for these early computers, and TLE may be one of them. Sometimes the custom-made extensions became mainstream. – dirkt Dec 20 '20 at 10:26
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    @dirkt That may well be the case. Apparently Knuth's installation also had an extra set of console switches accessible as location 8004 (source: Knuth's article "The IBM 650: An Appreciation from the Field"; he mentions that the feature is unique as far as he is aware). – texdr.aft Dec 20 '20 at 10:34
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    Note: The Knuth article I referred to in my previous comment is freely accessible here. – texdr.aft Dec 20 '20 at 16:03

The TLE instruction is a modification of the TLU instruction.

TLU (Table LookUp) (Opcode 84) compared a word with a series of consecutive words on the drum and finished as soon as an entry was found being equal or higher. It was meant to find a point in a sorted list.

TLE (Table Lookup Equal) (Opcode 63) is a modification of TLU stopping only when equal, which is useful to find a known entry in an unsorted list.

TLE is essentially executing TLU, but suppressing assessment on higher. It was available from IBM as 'add on' at USD 25 per month, as mentioned on page 375 of the BRL Report 1115 of 1961.

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    Wow. So it is. Thanks; I didn't know that that publication even existed. Purchasing a single new instruction is an interesting concept. You wouldn't happen to know the specifics of the "modified branch on distributor", would you? Presumably an alteration of operations codes 90..99 (I hope). – texdr.aft Dec 20 '20 at 15:43
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    Ah ja, Ed's site is grea - and so is he. Maybe just ask him. Say a hello from Hans. I do not have much knowledge about the 650. My era starts with the /360 :) Just happen to have a few books shelfed - and all these third party comparison lists are among the most useful. Selling add on instructions are a core business for IBM until today. IMHO the whole reason why the term CISC exists :)) – Raffzahn Dec 20 '20 at 15:49
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    And it's $25/mo. -- you're renting the instruction. I wonder what happens when you don't want to rent it any more. – another-dave Dec 20 '20 at 16:39
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    @another-dave No issue, then an IBM field engineer will come and disable it. – Raffzahn Dec 20 '20 at 17:04
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    @OwenReynolds Service doesn't mean they are coming once a month - especially not back then. More likely there was a FE always at site or within short distance. Nonetheless, they wouldn't act on their own, but get a note from sales what to install, activate or deactivate and come accordingly. – Raffzahn Dec 20 '20 at 22:14

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