🚀 go-pugleaf

> Heh... I was talking to one of the Livingston techs last week and got a laugh
> out of the 'why' we should use a modemless PM3 for a router instead of an IRX:
> 
> "The IRX has a 386/33.... the PM3 has a 486/66!"
> 
> And here I look at our Cisco with a 150Mhz RISC chip, special ram for IO
> controllers, etc.
[edited]

The instruction set, type of perpherials, I/O bus, RAM bus, etc all
affects performance.  A 1,000Mhz processor using 8 bit ISA bus devices
is probably going to be noticably slower then a 486 using PCI bus devices.

I don't know the RISC set in the Cisco, but say it has to move large
blocks of data around in RAM.   RISC chips tend not to have a move
character instruction for moving block of data so the RISC might have
something like the following (example does not necessarily reflect the
actual Cisco RISC or the Intel 486):

setup for move (1 to 10 instructions maybe)
load word
store word
increment counter
check counter to continue loop
cleanup after loop (0 to 10 instructions maybe)

a CISC processor like the 486 (I don't know 486 machine code) might have
a move character instruction so you have:

setup for move (1 to 5 instructions)
move block of data (1 instruction)

so the 486 may be able to move 512 bytes with 2-4 instructions while the
RISC processor may take around 500 instructions (assuming a 4 byte word).

-- 
Richard Shetron  multics@wizvax.net multics@acm.rpi.edu
                 What is the Meaning of Life?
There is no meaning,
It's just a consequence of complex carbon based chemistry; don't worry about it
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