Path: utzoo!utgpu!attcan!uunet!husc6!ukma!uflorida!beach.cis.ufl.edu!seeger
From: seeger@beach.cis.ufl.edu (Charles Seeger)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 286-based accelerator boards -- followup
Message-ID: <16776@uflorida.cis.ufl.EDU>
Date: 27 Jul 88 16:48:30 GMT
References: <14742@shemp.CS.UCLA.EDU> <22465@amdcad.AMD.COM>
Sender: news@uflorida.cis.ufl.EDU
Reply-To: seeger@beach.cis.ufl.edu (Charles Seeger)
Organization: UF EE Department
Lines: 42

In article <22465@amdcad.AMD.COM> phil@amdcad.UUCP (Phil Ngai) writes:
>In article <14742@shemp.CS.UCLA.EDU> wales@CS.UCLA.EDU (Rich Wales) writes:
>about the choices for upgrading his turbo XT clone.
>
>I have heard that most of the disk speed up between XT and AT is due
>to faster seek times on the AT disk itself. There are those who claim
>the 16-bit bus does not make disk IO much faster, although it does
>make a difference for memory accesses. If you figure the disk can
>deliver either 5 or 10 million bits per second and the memory can
>deliver 16 or 32 million bits per second (either a byte every 500 ns
>or two bytes every 500 ns) then you wouldn't expect an 8-bit disk
>controller to be too much of a bottleneck. 

But, the speed of the controller itself is *really* important, i.e. can
it handle the full disk speed (1:1 interleave)?  For most applications,
disk transfer rate is more important than access time.  My 1:1 RLL
(7.5 Mbps) controller gives cheap speed, in my 20 MHz 386/387 2MB box
(~$3500.00).  Such controllers are too fast for 8 MHz 8 bit buses.
Afterall, the HDC can't have all the bus bandwidth.

>If you do decide to choose an AT clone motherboard, I would look for
>something that allowed you to split 1 meg on the motherboard into 640K
>for DOS and 384K for LIM expanded memory. Boards built around the new
>CHIPS NEAT chip set are in this category. 

I prefer to use that 384K to shadow the system BIOS into faster RAM.
It really speeds memory checking, BIOS video, etc.  The NEAT chips do
this.  My AMI BIOS doesn't copy my HDC BIOS into RAM (it does the main
BIOS), but my disk performance should go up a significant bit when I
write the code to do it.

>We haven't even begun to discuss the 386...

 ..., which can, with the right software, emulate LIM in extended memory.
 They are sooo nice, but if you don't need high 32 bit performance, it'll
 be interesting to see what happens with the 386SX.

 Personally, I wouldn't get a accelerator board.  You can put together
 a new turbo AT clone for ~$1500.00, and sell your old turbo XT for
 ~$400.00.  Really, not much more $.

Chuck