Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!rosie!next.com
From: John_Graves@next.com (John Graves)
Newsgroups: comp.sys.next
Subject: Re: How much will parity slow down my NeXT?
Keywords: parity, DRAM, next
Message-ID: <1000@rosie.NeXT.COM>
Date: 20 Jun 91 00:07:30 GMT
References: <1991Jun15.145757.16931@wam.umd.edu>
Sender: news@NeXT.COM
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Nntp-Posting-Host: graves.next.com

For NeXTcubes and NeXTstations, enabling parity memory will add one clock cycle  
to the access time to each 32 bit word for both reads and writes initiated by  
either the processor or the DMA.

For NeXTstation Color, enabling parity memory will add one clock cycle to the  
access time to each 32 bit word for reads initiated by the processor.  Parity  
memory does not effect the performance of processor writes or DMA operations.

Parity applies only to DRAM (main memory), not to VRAM (video memory).  Parity  
does not effect anything which fits in the processor's cache (like small  
benchmarks).  Parity can only be used if all banks of DRAM contain parity SIMMs  
and parity is enabled in the bootROM (v63 or later).

What does this jargon mean?  You'll feel some performance degradation when  
using parity memory on NeXTcubes and monochrome NeXTstations, with a less  
noticeable effect on NeXTstation Color machines.

-

John Graves               NeXT Computer, Inc.
Hardware Engineer         900 Chesapeake Drive
John_Graves@next.com      Redwood City, CA   94063