On Sat, 10 Mar 2018 13:16:18 -0600, Michael J. Mahon wrote:

> Scott Lurndal  wrote:
>> Jack Fearnley  writes:
>>> On Fri, 09 Mar 2018 18:29:25 +0000, Scott Lurndal wrote:
>>>
>>>> Dennis Lee Bieber  writes:
>>>>> On Fri, 09 Mar 2018 17:16:19 +0100, David Brown
>>>>> 
>>>>> declaimed the following:
>>>>
>>>>> 
>>>>>
>>>>> There is always the convention used by Xerox Sigma Fortran-IV.
>>>>> Non-recursive, non-stack...
>>>>>
>>>>> Arguments were passed by putting them immediately after the CALL
>>>>> (branch and link opcode, and referenced by return address (saved in
>>>>> a register; I think 15 was the standard) + index.
>>>>
>>>> This was very common in the 1970s.   The PDP-8 had similar parameter
>>>> passing as did the Burroughs B2500 and descendents until the early
>>>> 80's when a re-entrant call (Virtual Enter (VEN)) was added to the
>>>> architecture.
>>>>
>>>> Unix system calls (UnixV6 on the PDP-11) embedded the system call
>>>> arguments in the instruction stream following the system call
>>>> instruction.
>>>>
>>>> The B2500 system call instruction (BCT) had the following general
>>>> form:
>>>>
>>>> BCT NNNN           # NNNN selects the system call BUN +Skip # Branch
>>>> Unconditional to after the parameters ACON label         # first
>>>> parameter (address constant)
>>>> DATA 2 UN 01       # second parameter, two digit numeric, value 01
>>>> .Skip
>>>>
>>>> The operating system would bump the return address by the size of the
>>>> branch instruction (8 or 10 digits) to get the parameters.
>>>
>>> Even further back. This was the standard method in the IBM1401 which I
>>> was programming in 1960.
>>
>> The B2500 dates back to 1965, and it did have a 1401 compability mode
>> :-)
>>
>>
> Not a compatibility mode, but a software emulator (which was little used
> by 1967).

From what I've been told about the B2xxx and B3xxx mainframes by people
who were developers on them they went a lot further than that -
effectively providing a set of VMs for running applications in, e.g.
Fortran programs ran in a stack-based environment with word addressed
memory while COBOL programs ran in a (possibly) stack-free environment
with byte-addressed memory. So, if they used VMs that way internally, it
would seem natural if they had a 1401 VM (ant several others for other
architecture

Me? I've never even set eyes on a Burroughs B-series mainframe. The
nearest I came to that sort of experience was using a 2966 that ran two
very different architectures simultaneously: George 3 and its applications
in a single VM [word addressed RAM using 24 bit words, 6 bit ISO
character codes, no stack]  and VME/B and its applications in a set of VMs
[byte addressed RAM, EBCDIC character codes and a stack-based
architecture] and two operator's consoles - one for G3 and a second for
VME/B


--
Martin    | martin at
Gregorie  | gregorie dot org

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