Subj : Hercules - Mainframes Emulator
To   : Miken
From : tenser
Date : Mon Apr 24 2017 21:53:00

On 04/24/17, Miken said the following...
 
 Mi> Please correct me if I'm wrong... but PDP is programmed by switches. That
 Mi> means there is not any possibility to type in any semantically more
 Mi> complex sentences. It's not that I wouldn't be able to comprehend in a
 Mi> bunch of time on how to handle it. But it's too far away from my
 Mi> understanding of the World. And I'm sorry for it. My nature is more
 Mi> language orientated than mathematical. I'm trying to "talk" to machines.
 Mi> And it's not really a natural thing to talk in ASM. Whatever I hope I
 Mi> didn't insult You or so.

Wow, there's a lot of misinformation floating around here.

PDP-series machines were produced by Digital Equipment Corporation (and its
successors).

The PDP line of processors was actually a family of machines. The PDP-6 and
PDP-10 were mainframe-class machines; the -11 was a minicomputer, and the -8
and -7 were often used in industrial control applications. Most of the PDP
family machines were word-oriented; the -11 was byte-oriented (that is, bytes
could be individually addressed by the CPU, as opposed to whole words of
memory with special instructions to manipulate bytes inside of the word). The
PDP-1 was the first in the line and was arguably NOT mainframe-class. The -6
and -10 used a 36-bit word (chosen to be competitive against mechanical
calculators of the era, which had 9 significant digits: 36-bits are
sufficient to store 9 4-bit BCD digits). The -11 had a 16-bit word; the -7
had an 18-bit word and the -8 had a 12-bit word.

The PDP-7 is perhaps most notable for being the machine that Ken Thompson
originally wrote Unix on (after Bell Labs pulled out of the Multics project
that targeted the 36-bit GE-645 machine - another word-oriented
mainframe-class machine).

The most famous of the PDP series of computers were undoubtedly the -10, on
which much of the early ARPANet and Internet work was done, and the -11, on
which much of the early Unix work was done. Ken and Dennis Ritchie moved Unix
to the PDP-11 fairly quickly. While some of the very early PDP machines did
have front-panel switches, most often one interacted with them via terminals
connected to serial ports. The VAX series of computers were introduced as a
successor to the PDP-11 and used a 32-bit word and 32-bit virtual address
space. They ultimately took over much of Digital's 36-bit business as well.

Hercules is a mainframe emulator, where it is understood that "mainframe"
means "IBM mainframe". It implements the z/Architecture instruction set and
emulators for many mainframe peripherals. z/Architecture is the successor to
the S/390 instruction set, which succeeded the S/370, which succeeded the
S/360 which succeeded a number of early IBM machines such as the 7094, which
was a 36-bit word-oriented machine. System/360, introduced in the 1960s, was
byte-oriented with 32-bit registers and, I think, a 20- or 24- bit address
space (I could be wrong). 370 was a 32-bit machine; z/Arch is a full 64-bit
machine. When most people refer to "mainframes" they mean IBM and compatible
mainframes using one of these instruction sets; most of IBM's traditional
competitors in the space are gone. The only remaining competing architecture
seems to be Unisys 1100-series machines, which are themselves successors of
CDC machines. IBM also had a number of mid-range system options, including
System/36 et al and AS/400, but these are not instruction-set compatible with
their mainframe systems. Note that most mainframes also support terminal
access; one can even run Unix on some of them. VM/370 -> VM/CMS -> VM/ESA ->
z/VM is probably the most familiar environment for mainframe access for most
modern users; the other popular options were the timesharing option for the
batch MVS operating system (MVS/TSO succeeding, if I recall, TSS/360). Modern
mainframes often run Linux under z/VM.

Anyway, the point is that DEC, IBM, Unisys/CDC and GE/Honeywell/Bull
mainframes are all distinct systems and most are accessed interactively.

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