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From: eric@caip.RUTGERS.EDU (Eric Lavitsky)
Newsgroups: net.micro.amiga
Subject: Re: Amiga's listening to you.
Message-ID: <192@caip.RUTGERS.EDU>
Date: Wed, 23-Oct-85 22:59:50 EDT
Article-I.D.: caip.192
Posted: Wed Oct 23 22:59:50 1985
Date-Received: Sat, 26-Oct-85 05:03:45 EDT
References: <132@amiga.amiga.UUCP> <819@utai.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 43

> From: wjr@utai.UUCP (William Rucklidge)
> Newsgroups: net.micro.amiga
> Subject: Re: Amiga's listening to you.
> Message-ID: <819@utai.UUCP>
> Date: 22 Oct 85 18:36:34 GMT

> Hum... this raises some questions. From the block diagram I saw in BYTE,
> it seems that the Amiga has a layered bus structure. Does anyone know if
> this is in fact the case? This would mean that the processor would only
> be slowed down/locked out when it was trying to access the lower 512K
> bank, and could run at full speed if it was using other memory, regardless
> of what display mode was active or what the blitter was doing... if you
> had an external RAM expansion you would be able to run the processor at
> full speed almost all the time, since your programs would be in non-
> contended memory.
> 
> This would be a lovely thing to have... full processor speed and lots
> of bit planes and blitter action.
> 
> -- 

You are correct. The lower 512K of the address space is known as 'chip' 
memory. The 3 custom VLSI's can only see this memory. All memory added
above an beyond this is called 'fast' memory, because the 68000 can
access this memory at full speed without worrying about contention from
other devices. In fact, if you look at the board design, it strongly
reflects this feature of the architecture. Any memory added on the 
side expansion port is linked directly to the 68000, but not the VLSI's
like the internal 512K is. 

 Applications that sit in fast memory should really scream, even when
a lot of graphics is going on. Hopefully, Commodore will announce their
expansion box soon so we can fully take advantage of the Amiga's address
space. The T-Card may be nice, but if I expand, I want to be able to 
go all the way...

Eric
-- 

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