From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <44553B66.5010604@lanl.gov>
Date: Sun, 30 Apr 2006 16:34:14 -0600
From: Ronald G Minnich <rminnich@lanl.gov>
User-Agent: Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929)
MIME-Version: 1.0
To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu>
Subject: Re: [9fans] nvidia scrolling performance
References: <04c347e8d648750d2e5c10d133a878b9@quintile.net>
In-Reply-To: <04c347e8d648750d2e5c10d133a878b9@quintile.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Topicbox-Message-UUID: 4b66063c-ead1-11e9-9d60-3106f5b1d025

Steve Simon wrote:

> I may be talking rubbish but I understood this is a fundamental
> problem with reading VGA memory over the PCI bus. VGA cards are
> designed for fast writes and not fast reads.

depends.

on pci and AGP it's an issue.
AGP has the assymetric bandwidth built in.

on PCI express, it's supposed to get much better.


> I do hear that some cards are appearing with dual PCIX which will allow
> symetric access speeds to the frame buffer.
>

Note that PCIX is not pci express (PCIe or PCI-e or PCI-E). It's so
confusing. PCIX is PCI-X which is an old, slow bus.

ron