Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!batcomputer!cornell!rochester!rutgers!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: My A3000/25/50 seems a bit slow... Why?
Message-ID: <21451@cbmvax.commodore.com>
Date: 9 May 91 19:07:08 GMT
References: <1991May8.022802.19449@coplex.uucp> <8934@ucdavis.ucdavis.edu> <1991May9.085003.20421@cs.umu.se>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 40

In article <1991May9.085003.20421@cs.umu.se> dvljrt@cs.umu.se (Joakim Rosqvist) writes:
>In article <8934@ucdavis.ucdavis.edu> zerkle@iris.ucdavis.edu (Dan Zerkle) writes:
>>In article <1991May8.022802.19449@coplex.uucp> dean@coplex.uucp (Dean Brooks) writes:

>>>  I just bought my Amiga 3000 25MHZ 50MB, and everything seems to be working
>>>great.  The only thing is that I was expecting many program to be BLAZINGly
>>>fast.  It seems to be a bit on the slow side, especially for a 25MHZ version.

>>How much memory do you presently have in it?  If you have just the 2
>>megabytes that came with it, that's the reason.  

>Is this because CHIP-ram is busy with other things than running programs
>or is the CHIP ram clocked at 3.58 Mhz even on a 3000??

Both, actually.  Chip RAM on an A3000 runs the same type of cycle as on an
A2000, this enforced synchronous memory cycle controlled by Agnus.  The memory
is 32 bits wide, so it's effectively twice as fast as on an A2000, but still
slow.  It might help to look at numbers.  While the custom chips can Chip RAM
every 280ns, the CPU only gets every other cycle, at best, so its cycle time
to Chip RAM is 560ns.  On a 25MHz A3000, the same 32 bit access runs in 200ns.
With static column DRAMs and burst, that's reduced to an effective 110ns
per longword.  So that makes Fast RAM somewhere between 3x and 5x faster than
Chip RAM, even when Chip RAM isn't loaded down with lots of video fetch,
blitter, or copper activity.  And Fast RAM, of course, never gets loaded down.
So, basically, you want Fast RAM in your A3000 for anything that doesn't
absolutely have to live in Chip RAM.

This is really the same on practically every computer, they just don't make
their "Chip RAM" flexible enough to contain anything but a video display.  You
wouldn't, for example, run programs out of the display buffer in a VGA card
on a PC Clone.  This will always be the case on Amigas.  Even with faster
systems way in the future, Chip RAM will always be optimized for the needs of
the video chips, while the Fast RAM will always be optimized for the needs of
the processor bus (CPU, FPU, DMA for SCSI, whatever else lives here).


-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
      "That's me in the corner, that's me in the spotlight" -R.E.M.