From: John Ahlstrom on
Andrew Swallow wrote:
> David Kanter wrote:
> [snip]
>> A much more reasonable, and possibly true, assertion would be that the
>> advantage of RISC architectures decreased over time. However, even as
>> late as the Pentium 1, there was a huge advantage for RISC
>> architectures. With the Pentium Pro that became less clear, although
>> RISCs still ruled the roost for FP heavy applications.
> We can certainly have a nice debate as to whether anything containing
> floating point hardware is RISC.
> Andrew Swallow

> ====REPOST====
> Article 22850 of comp.arch:
> Path: mips!mash
> Subject: Nth re-posting of CISC vs RISC (or what is RISC, really)
> Message-ID: <2419(a)spim.mips.COM>
-- snip snip

> 3a) Have 1 size of instruction in an instruction stream
> 3b) And that size is 4 bytes
> 3c) Have a handful (1-4) addressing modes) (* it is VERY
> hard to count these things; will discuss later).
> 3d) Have NO indirect addressing in any form (i.e., where you need
> one memory access to get the address of another operand in memory)
> 4a) Have NO operations that combine load/store with arithmetic,
> i.e., like add from memory, or add to memory.
> (note: this means especially avoiding operations that use the
> value of a load as input to an ALU operation, especially when
> that operation can cause an exception. Loads/stores with
> address modification can often be OK as they don't have some of
> the bad effects)
> 4b) Have no more than 1 memory-addressed operand per instruction
> 5a) Do NOT support arbitrary alignment of data for loads/stores
> 5b) Use an MMU for a data address no more than once per instruction
> 6a) Have >=5 bits per integer register specifier
> 6b) Have >= 4 bits per FP register specifier

Debate over?

From: Rich Alderson on
nmm1(a) (Nick Maclaren) writes:

> The PDP-11 never made much impact as a 'general' computer, especially
> in the commercial arena, whereas the PDP-10 and PDP-20 did.

Point of order: There is no such thing in the DEC/Digital product line as a
"PDP-20". The highest number in the PDP series was the PDP-16.

Some people believe that if the PDP-10 ran Tops-10, then a machine running
Tops-20 must be a PDP-20, but the reasoning is flawed. Modulo some differences
in I/O, either operating system will run on the same hardware. I call to your
attention the bright orange box labeled "DECSYSTEM-20" on which I run Tops-10
for the PDPplanet project (

Rich Alderson | /"\ ASCII ribbon |
news(a) | \ / campaign against |
"You get what anybody gets. You get a lifetime." | x HTML mail and |
--Death, of the Endless | / \ postings |
From: Peter Flass on
Nick Maclaren wrote:
> It is a great pity that the new RISC systems (as distinct from previous
> inventions of the approach) concentrated entirely on making the hardware
> simple, often at the cost of making the software hell to get right.
> Which is one of the reasons that many aspects of modern software are
> so much worse than they were 25 years ago.

I, as a programmer, shouldn't have to worry about ordering the
instructions so as not to lose cycles (pipeline slots, whatever.)
That's what hardware/microcode is for.

From: Peter Flass on
jmfbahciv(a) wrote:
> And I'm telling you, again, that DEC did not have the infrastructure
> to handle that support. DEC's main business was not retail-ish.

Even IBM decided they didn't want to be in this business.

From: Peter Flass on
Nick Maclaren wrote:

> |> Yeah I seem to recall there being a couple of PDP11s hooked to a
> |> 370 in the early 1980s (and late 1970s) not far from you.
> Yup :-) And we weren't the only such site, because those mainframes
> were dire for single-character interactions and related communications
> work and peripheral driving.

Series-1's were also in this market. IBM sold them with an IUP as a
terminal driver. "Yale ASCII" or something like that.