Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!uakari.primate.wisc.edu!sdd.hp.com!cs.utexas.edu!ut-emx!ccwf.cc.utexas.edu
From: greg@ccwf.cc.utexas.edu (Greg Harp)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: NeXT software size
Message-ID: <48816@ut-emx.uucp>
Date: 11 May 91 07:09:20 GMT
References: <48808@ut-emx.uucp> <-h6Hqu=@cs.psu.edu>
Sender: news@ut-emx.uucp
Reply-To: greg@ccwf.cc.utexas.edu (Greg Harp)
Organization: The University of Texas at Austin
Lines: 77

In article <-h6Hqu=@cs.psu.edu> melling@cs.psu.edu (Michael D Mellinger) writes:
>
>   Hmmm...  How many waits does the memory require?  I'm really amazed because
>   I've seen 80ns RAMs make a big difference in 030 boxes.  The recommended
>   ZIPs for the A3000 are 70ns, with a static column mode that makes the
>   access time much faster (45ns?) when you access the same memory column.
>   BTW, the going price for these is about $28 a module, and you need eight at
>   a time making the price $224 for four megs.  At that price I've basically
>   considered it part of the purchase price for when I buy my 3000.
>
>   Why on Earth would NeXT use such slow memory?  I'm literally shocked...
>
>There might be a wait state, but I don't know.  I haven't heard
>anything about it one way or the other.  Anyone know if a wait-state
>is required for a 25MHz 040?  The Amiga might need faster RAM because
>it has to share memory with the blitter(I'm just guessing, not an EE).
>Only the first two megs are chip RAM on the newer models, of course.

Well, the Amiga has two types of memory.  There's Chip RAM and Fast RAM.
The names practically describe what the difference is, but I'll give you
the low-down.  

Chip RAM is shared by the custom chips and the CPU.  It runs at the speed
of the custom chipset (currently 7.14Mhz in NTSC machines) and I believe
the CPU can access it every other cycle.  Because the memory has to be
shared, it is slow to access.  You don't want to run programs on an 030 box
out of Chip RAM.  

Fast RAM is memory that is only accessable by the CPU.  It runs at the
speed of the CPU (unless, of course, you are using an A2000 with an 030
card in the CPU slot and a 16-bit memory card in a Zorro II slot).  Fast
RAM is, therefore, fast.  

Also, the first two megs of the A3000 are not necessarily Chip RAM.
It's true that there is space for 2MB of Chip, but the A3000-25/50
ships with 1MB Chip/1MB Fast.  You move the meg of Fast over to the
Chip bank when you put more memory into the machine, giving you 2MB of
Chip and whatever amount of Fast you bought (up to 16MB on the
motherboard).  Also, the A3000 is not the only Amiga with separate
Chip and Fast RAM.  All Amigas are built like this.

This architecture allows the CPU and the blitter to function independantly
without affecting eachother (except for the CPU setting up the blitter
registers, of course).  This is why an Amiga using an equivalent CPU to
another machine tends to outperform it, especially where graphics and
sound are involved.

BTW, faster memory chips aren't _required_ in an Amiga.  It basically
doesn't make sense to buy slower chips, though.  The price difference is
very small nowadays.  In fact, when I bought my memory board the company
put 80ns memories in it (I'd normally put them in myself, but they had a
decent package price).  Now, a 7.14Mhz 68000 doesn't need 80ns RAM, nor do
I think it can make use of the extra speed.  They explained that they no
longer even buy slower RAMs.  They didn't charge me a higher price than
their list for 100ns chips, so I had no reason to complain.

I'm no EE, either, but I think a 25Mhz 040 using 100ns RAM would be at
least a one-wait-state configuration.

>To reduce cost is probably the reason why NeXT would add a wait state.
>Apple always seemed to have a wait-state or two in their machines too.
>I see the NeXTstation as the SE of NeXTs line.  Over the next couple
>of years it will decrease in price until it fills the void at the
>low-end.

Well, I wouldn't use Apple as an example of what's a good practice in
computer manufacturing.  Remember that A/UX is still SVr2... :)

Anyway, I don't understand what makes using slower RAMs that much cheaper.
The memories themselves woudn't be much different in price in that kind of
volume.  Is it an architecture thing?  Anyone?  Anyone?  

Greg
-- 
       Greg Harp       |"I was there to match my intellect on national TV,
                       | against a plumber and an architect, both with a PhD."
greg@ccwf.cc.utexas.edu|            -- "I Lost on Jeopardy," Weird Al Yankovic