PDP-11 or PIC?

gareth

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Jun 21, 2012, 1:37:30 PM6/21/12

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Going back to my copy of the 1970 PDP-11 handbook, it appears to have
been available in two versions, the 11/20 with 4K words (8K bytes) of
memory,
and the 11/10 with 128 words of R/W memory and 1K words of some
form of ROM.

256 bytes of RAM and 2K bytes of ROM?

Well exceeded by most of the PICs of today!

Walter Banks

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Jun 21, 2012, 2:37:09 PM6/21/12

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The initial PDP-11 changed its name to PDP 11/20 as other models
came into being. My lab had PDP-11 serial number 185 and another
in the low 200's Both did not have the /20 later by serial number 400
or so they were called PDP-11/20

The PDP11 could treat any location as data or program store.
PIC's by and large are data store poor and data access on a
PIC is expensive in cycles and code compared to the PDP11.

w..

Joe Pfeiffer

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Jun 21, 2012, 2:58:03 PM6/21/12

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True, but the intent is to implement lookup tables in code. My
experience is that surprisingly little RAM is needed for the sorts of
projects I undertake.

Rod Speed

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Jun 21, 2012, 3:00:40 PM6/21/12

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gareth <no....@thank.you.invalid> wrote

> Going back to my copy of the 1970 PDP-11 handbook, it appears
> to have been available in two versions, the 11/20 with 4K words
> (8K bytes) of memory, and the 11/10 with 128 words of R/W
> memory and 1K words of some form of ROM.

That rom was a full unibus card with diodes you
clipped with sidecutters with mine of that vintage.

> 256 bytes of RAM and 2K bytes of ROM?

> Well exceeded by most of the PICs of today!

But you cant program it with sidecutters.

gareth

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Jun 22, 2012, 4:07:03 AM6/22/12

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"Rod Speed" <rod.sp...@gmail.com> wrote in message
news:a4h9bj...@mid.individual.net...
> gareth <no....@thank.you.invalid> wrote

>> 256 bytes of RAM and 2K bytes of ROM?
>> Well exceeded by most of the PICs of today!
>
> But you cant program it with sidecutters.

The "Halt Forever" pseudo instruction?

gareth

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Jun 22, 2012, 4:10:50 AM6/22/12

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"Walter Banks" <wal...@bytecraft.com> wrote in message
news:4FE369D5...@bytecraft.com...

But in terms of anything you might wish to do, then the functional
capability and
speed of operationod the PICs exceed that of the early PDP-11. ISTR that the
longest
instruction time (save that of RESET which was 50mSecs) took 17.6 uSecs,
which
correct me if I am wrong, was something like BICB @(r0)+, @(R1)+

Rod Speed

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Jun 22, 2012, 5:37:39 AM6/22/12

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gareth <no....@thank.you.invalid> wrote
> Rod Speed <rod.sp...@gmail.com> wrote

>> gareth <no....@thank.you.invalid> wrote

>>> 256 bytes of RAM and 2K bytes of ROM?
>>> Well exceeded by most of the PICs of today!

>> But you cant program it with sidecutters.

> The "Halt Forever" pseudo instruction?

Nope, you could program those that way to do
anything you could put in thru the front panel.

Walter Banks

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Jun 22, 2012, 7:08:04 AM6/22/12

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I understand where you are coming from. It probably would be important
to define which PIC you are referring. Most of the PIC's in use today are a
small RISC with 8 bit data and 12 to 16 bit instruction paths. The recent
PIC 24 and PIC 32 are entirely different processors

In raw computing power the PIC and an early PDP-11 are in the same ball
park. The PDP-11 was a slower 16 bit computer and teh PIC uses 8 bit
data paths. The PDP-11 is at a disadvantage when it is used to impliment
applications well suited for a PIC. There are applications in real time that
the PDP-11 could and was used that it would seriously out perform a PIC
and it might be questionable if a PIC could be used.

The PDP-11 was a well implemented 16 bit processor well suited to control
numerical control machines, an application that most of the PICs until
PIC24 and PIC32 became available would find difficult.

w..

gareth

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Jun 22, 2012, 7:25:46 AM6/22/12

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"Rod Speed" <rod.sp...@gmail.com> wrote in message

news:a4iso1...@mid.individual.net...

I think you may have missed the intended jest.
(Sidecutters to remove the chip from the board)

gareth

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Jun 22, 2012, 7:26:59 AM6/22/12

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"Walter Banks" <wal...@bytecraft.com> wrote in message

news:4FE45214...@bytecraft.com...

> The PDP-11 was a well implemented 16 bit processor well suited to control
> numerical control machines, an application that most of the PICs until
> PIC24 and PIC32 became available would find difficult.

But not in the original configuration which was the subject of this
discussion

Rod Speed

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Jun 22, 2012, 3:32:12 PM6/22/12

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gareth <no....@thank.you.invalid> wrote
> Rod Speed <rod.sp...@gmail.com> wrote
>> gareth <no....@thank.you.invalid> wrote
>>> Rod Speed <rod.sp...@gmail.com> wrote
>>>> gareth <no....@thank.you.invalid> wrote

>>>>> 256 bytes of RAM and 2K bytes of ROM?
>>>>> Well exceeded by most of the PICs of today!

>>>> But you cant program it with sidecutters.

>>> The "Halt Forever" pseudo instruction?

>> Nope, you could program those that way to do
>> anything you could put in thru the front panel.
>
> I think you may have missed the intended jest.

Nope. I can nit pick even jokes.

> (Sidecutters to remove the chip from the board)

Yeah, that was obvious.

Walter Banks

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Jun 22, 2012, 4:20:06 PM6/22/12

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I was talking about the original configuration. The combination of 16 bit
word with good 8 bit support and a well implemented instruction set made
the original PDP-11 a significant computer for a wide range of applications.

I mentioned the numerical control application because it was an
application that I was familiar with. The PIC could implement small
control and data handling applications. The PDP-11 had paper tape
readers and at the time a TTY console making it flexible for many
applications the PIC's for the most part until very recently could not
easily do.

I know both processors well. I ran a lab in the 70's that eventually had
11 PDP-11's in it including 2 of the original PDP-11's. In the 90's I
wrote a C compiler that targeted code for the 12,14,16 bit Microchip
PIC cores and worked on the instruction set design for the extended
14 bit core and wrote a compiler for it 2 or 3 years ago.

Walter..

gareth

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Jun 22, 2012, 4:55:40 PM6/22/12

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"Walter Banks" <wal...@bytecraft.com> wrote in message

news:4FE4D376...@bytecraft.com...

> I mentioned the numerical control application because it was an
> application that I was familiar with. The PIC could implement small
> control and data handling applications. The PDP-11 had paper tape
> readers and at the time a TTY console making it flexible for many
> applications the PIC's for the most part until very recently could not
> easily do.

The PDP-11 with added I/O beats the PIC without any I/O?

Yeah, right.