Newsgroups: comp.os.os2.misc,comp.sys.ibm.pc.hardware
From: rbroders@oracle.com (Robert Brodersen)
Subject: Re: 50DX vs 66DX2 and OS/2
Followup-To: comp.os.os2.misc,comp.sys.ibm.pc.hardware
Organization: Oracle Corporation, Belmont, CA
Date: Fri, 2 Oct 1992 02:10:58 GMT
X-Disclaimer: This message was written by an unauthenticated user
              at Oracle Corporation.  The opinions expressed are those
              of the user and not necessarily those of Oracle.


>1. A multitasking OS will have lots of memory access outside the chip
>(and probably outside the SRAM cache, as well). Thus, the 33MHz external
>speed of the 66DX2 will give slower performance than the 50. I will not
>be running real MSDOS at all, so my only criterion is where I get the
>best performance in a multitasking, OS/2 environment.

Actually, this isn't really correct.  Once you go outside the SRAM
cache, you are slowed to DRAM (50, 60, 70 or more nanoseconds) speed.
Even the laggardly 33MHZ external speed of the 66DX2 is much faster
than the fastest DRAM (30 ns << 50 ns).  I have heard of 43 ns DRAM,
but never seen a system which uses it.

>2. On the other hand, for operations that don't access main memory, the
>66 will obviously be faster, and there are sure to be plenty of these,
>as well.

Again, this is a little flawed.  For applications which use the
secondary (SRAM) cache extensively, the 50MHZ DX will have an edge.
The SRAM (typically ~15ns) can keep up with the 50MHZ (20 ns)
processor quite nicely.

>3. My dealer is charging $135 more for the 66 than the 50.

>4. There has been occasional talk of a 100DX2. If this is likely, I
>preserve an upgrade path by selecting the 50 now.

The only thing I have heard about the 100DX2 has been intel denying
that they will make one, and people claiming that it would have too
much FM radio interference if they did.

Perhaps a more likely upgrade would be the P24T.  This is supposed to
be a P5 (wish they'd hurry up with the name) with a 32 bit external
data bus (64 bit internal), and a 33 MHZ external clock (66 MHZ internal).
Some motherboards (ZEOS) have a ZIF (zero-insertion-force) CPU socket
with extra pins to support the P24T chip.  I have heard that most of
these do not support the full functionality of the chip (i.e. write-back
cache support), but I am not sure.  The P24T would probably outperform
the 100DX2 in integer instructions because of its larger on-chip
cache, wider data paths, and dual pipelines.  Floating point point
performance is supposed to be 8 times that of a comparably clocked 486.

The other concern would be moving data around at high speeds.  Where
are you moving it?  Probably to the disk controller, or to the display.
A Local Bus solution would be ideal for both of these!  However, the
VESA VL-Bus specification only supports 33 MHZ.  Again, the DX2 looks
like the best solution to your problems.  Look for a VL-Bus
motherboard with a P24T socket and you should be in good shape.
50 MHZ sounds better, but with todays DRAM technology it doesn't
really do much for you (unless you have a nice SRAM cache).

--
Thanks-           rbroders@oracle.com       -Bob Brodersen (415)-506-2189
Applications Architect, Applications Technology Group, Applications Division
                  Oracle Corporation, Redwood Shores, CA 94065
Newsgroups: comp.os.os2.misc