if you hadn't already known this about the PDP-8

From: Chris Kennedy <chris_at_mainecoon.com>
Date: Thu Dec 13 11:46:16 2001

Gunther Schadow wrote:

> I found this really interesting: The PDP-8 has no concept of a
> stack. It does have sub-routines though.

This is pretty characteristic of machines of the time. The Nova
didn't grow a stack until the mid-70's, although the call linkage
was somewhat different with the return address being hammered into
AC3 rather than written to memory (although the interrupt return
address did get written to location zero).

> This is hillarious! Wasn't the notion of a stack arond already
> before 1965?

Of course. In machines frequently an order of magnitude
(if not even more) greater in cost.

> The coolest thing is that inspite of this "unique" way of handling
> subroutines, the PDP-8 had a timesharing system TSS-8.

The lack of hardware support for a stack abstraction hardly precludes
the construction of shared or reentrant code. So you have to
manipulate the stack yourself rather than the hardware doing it
for you. Big deal; for many people the options in the late 1960s
were to do that or not have a machine at all. The big problem
is doing useful things in the absence of a memory mapping and
protection unit of some sort (the Nova grew one early on, but
I'm too ignorant of the PDP-8 family to know if such an option ever

Chris Kennedy
PGP fingerprint: 4E99 10B6 7253 B048 6685  6CBC 55E1 20A3 108D AB97
Received on Thu Dec 13 2001 - 11:46:16 GMT

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