Re: ancient OS history, ARM is sort of channeling the IBM 360

According to Lawrence D'Oliveiro  <ldo@nz.invalid>:

possible to request “locate mode”, ...
* It only works for reads, not for writes

>
It works fine for writes on IBM systems. PL/I even has a LOCATE
statement to get a buffer to write into.

>
I found this manual
<http://bitsavers.trailing-edge.com/pdf/ibm/360/tss/GC28-2045-1_Time_Sharing_System_PLI_Language_Reference_Manual.pdf>.
On page 96, it says
>
   The LOCATE Statement
   --------------------
...

So it has its own limitations on applicability. For example, it only
seems to work for writes, not reads.

Well, yeah. Keep reading and on page 97 you'll find the SET option
which is how a you get the pointer for a locate mode READ. It was more
common when defining based data to say in the declaration what the
default pointer to the data was, so if you said to READ or LOCATE the
item, it'd automatically set the pointer.

That TSS manual is rather estoteric since hardly anyone ever used TSS
and even those of use who did, didn't write much PL/I.

Here's the regular PL/I manual which explains locate mode for
reading and writing on page 168.

https://bitsavers.org/pdf/ibm/360/pli/C28-8201-1_PLIrefMan_Jan69.pdf