Newsgroups: bit.listserv.win3-l
Date:         Wed, 8 Apr 1992 19:12:00 EDT
From:         ERIC WEBB <EWZ@NCCIBM1.BITNET>
Subject:      Re: DX Doublers

> In light of the new "power" in 3.1 and the forthcoming NT, I see a lot of adds
> in the Shopper about DX doubler chips.  On closer inspection of the ad (cf
> Gateway 2000's latest ad, the 50Mhz DX2 80846 is a 25Mhz 80846 running at
> 25Mhz externally and 50Mhz internally. I am sure that there is a reasonable
> explanation of the meaning of the speeds but what does it mean in English?

Tom,
  I believe the "clock-doubled", or DX2, chips have advantages on which
we can all agree; no water for flames required. Benchmark ratios among the
DX and DX2 chips vary. However, the DX2 is generally a bigger bang for
the buck. Gateway suggests its 50 mhz DX2 provides 35% more performance
than its similarly configured 33 mhz DX system, yet costs only $200 more.
If true, that is rather a good deal.

  One caveat: you may want to buy the 33 mhz system and wait for the
upcoming 33/66 "OverDrive" chip. This may be an even better bargain in
the long run because you can only install an "OverDrive" chip which runs
externally at the same rate as your system's external clock. Thus, you
won't be able to install a 33/66 mhz chip on a system with a 25 mhz
external clock. Some machines have all the external clock components on
a single card (e.g. PS/2 95), which can be swapped for any other CPU
card that the vendor offers. These upgrades can be quite expensive.

  I have found it difficult to locate direct comparison figures between
DX and DX2 chips with identical internal speeds. However, using some
assumptions, we can work out some numbers. Don't hold me to them; consider
the calculations a mental exercise ( is that waffling, or what ?)

  Most vendors advertise 50 mhz DX2 systems as 30-35% faster than a simularly
configured 33 mhz DX system. This may be optimistic, but lets use 30%
for arguments sake.  In order to compare the 50 mhz DX and 50 mhz DX2,
we must compute the EFFECTIVE mhz of the DX2.  Let x equal the effective
mhz:

   1. (x-33/33)*100 = 30
   2. (x-33/33) = 0.30
   3.  x-33 = 0.30*33
   4.  x-33 = 9.9
   5.  x = 9.9+33
   6.  x = 42.9 mhz

  The 50 mhz DX2 runs at an effective rate of 42.9 mhz. Now it is a simple
matter to compare the 50 mhz DX2 with the 50 mhz DX. Let p equal the
percentage additional effective mhz which the DX provides over the DX2:

   1. p=(50-42.9/42.9)*100
   2. p=(7.1/42.9)*100
   3. p=17%

  Gateway advertizes the 50 mhz DX2 system for $3195. Multipling the cost
by 1.17 yields $3738. I'm not sure where you could get a 50 mhz DX system
configured like the Gateway for $3700 (certainly not with good quality
components). Perhaps another list member knows of such a deal?

  As you would expect, running Windows on a faster CPU can speed up
Windows and application performance provided the CPU is the immediate
bottleneck. Often, using a faster CPU results in the video system becoming
the immediate bottleneck. Of course, we know to use graphics coprocessors
or accelerators to solve this problem.

  My advice is to upgrade  the video system with a good accelerator or
coprocessor as the first hardware step in improving Windows performance.
This should help you minimize cost when upgrading to a faster CPU.

Regards,
Eric Webb
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