🚀 go-pugleaf

From article <5221@ur-cc.UUCP>, by carlo@merlin.cvs.rochester.edu (Carlo Tiana):
> In article <1990Feb10.233412.15585@mathrt0.math.chalmers.se> d6maca@dtek.chalmers.se (Martin Carlberg) writes:
>>...
>>The article says that the 68040 is 25% faster than the 80486 at the same
>>clockspeed.
>>...
> 
> 
> While on the subject of "cross-sultural" comparisons (and with the caveat
> that I know just about nil about the internals of anything more complicated
> than a ball bearing): why is it that people are always quoting the number
> of wait states in 80xxx chips and never for 68xxx chips? This probably a
> silly thing to do, but how does my IIci rate compared to a say, an 80386
> machine runnng at 25Mhz with n wait states?

  Good question. Answer: because noone else sells Macs, so you can basically
have five machines to compare (Plus, SE, II__, IIx + IIcx + SE/30, and the IIci)
so who cares about wait states. Here's the low down...

Mac       Number of                  Ram speed for x wait states
Model     Wait States   CPU Speed    0   1   2   3
-------   -----------   ---------    --- --- --- ---
Plus      0                7.8MHz    130 260 390 520
SE        0                7.8        "   "   "   "
Portable  0               15.6        60 120 180 240
II__      1               15.6        "   "   "   "
IIx/cx*   1               15.6        "   "   "   "
IIci      2               25.0        40  80 120 160
????      ?               33.0        30  60  90 120
Mr RISC   0               50.0        20  40  60  80

* includes SE/30

Note: The second column is the result of what Apple gave us. The last columns
are what speed of RAM would be necessary to build a machine at speed X with
the given wait states. 

+ The IIci has a slot for a "cache card" which is basically memory fast enough
  to operate at 0 wait states, which allows the CPU to run more efficiently.
+ The Portable is unique in that all of its RAM is of the static variety (SRAM
  as opposed to normal dynamic RAMs, aka DRAM) so it operates at no wait states.
+ The problem with these fancy new RISC machines is that they operate at such
  high clock rates, the design of a cache system to keep them feed is one of
  the hardest (if not THE hardest) parts to getting the things to exploit the
  full capabilities of the CPU. When a RISC machine doesn't get memory when it
  wants it, it has to hold up an entire pipeline of instructions to do it, and
  consequently clobbers effective performance.


> 
> On a similar note (equally naive question): why does a 25 Mhz 68030 in my
> above-mentioned ci feel like it is nowhere near as fast as the 25Mhz 68030
> in the news server that allows me to post these silly questions? I
> certainly would not want other people logged into my Mac reading news while
> I was typing away at a Word document, because performance would just die
> (it's bad enough as it is -- though I guess I am spoiled).
> 
  Most likely because your news server doesn't happen to be supporting a
graphical interface between the CPU and yourself. A IIci is very much the
number cruncher of a computer. The reason why it doesn't always "feel" that way
is because doing something as simple as writing a line of text on the screen
involves manipulating about 500 bytes of data for 80 columns on a monochrome
screen. (That ignores the effort to do all the stuff like finding the font in
memory, finding the each character in the font as you draw each character, etc.)
 A text based system, on the other hand, manipulates 80 bytes of data to achieve
the same effect! (Side note: PC type people have bitched at software companies
about communication programs that are SLOWER, but are they're just ignorant of 
the extra overhead involved in drawing text as graphics under PM. :-) The
responsiveness of a the classic Mac in this light is nothing short of
incredible. Kudos to the original hackers at Apple! Now, when you do the same
thing with a color/greyscale monitor set to, say, 4 bits, you have to at least
four times the work, plus the OS on the Mac may have to convert a 1 bit deep
font to 4 bits, which takes time... So, THAT's why that darn news server feels
like greased lightning. I must admit, playing with the latest PCs in text mode
feels good, but you switch them to Windows, and it's like a Plus, but uglier.

Robert Minich
Oklahoma State University
minich@a.cs.okstate.edu

This school is too worried about other things to worry about little ole me, so
I can say what I want. It's that First Ammendment I keep trying to convince
that I try to convince the existence of to these guys here of that will get 
ME into trouble.