Newsgroups: comp.sys.amiga.advocacy Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!psuvax1!news From: melling@cs.psu.edu (Michael D Mellinger) Subject: Re: Blitter vs. 040 (was: Computer Architecture question In-Reply-To: caw@miroc.Chi.IL.US's message of 15 May 91 00: 56:18 GMT Message-ID: Sender: news@cs.psu.edu (Usenet) Nntp-Posting-Host: sunws5.sys.cs.psu.edu Organization: Penn State Computer Science References: <3310.tnews@templar.actrix.gen.nz> Date: Wed, 15 May 1991 08:46:56 GMT Lines: 69 In article caw@miroc.Chi.IL.US (Christopher A. Wichura) writes: Talking about dense! You just don't get it, do you? Using the blitter in parallel, even if it might be a bit slower than an 040 running balls out doing all your graphical work, does not necessarily make the 040 faster. You could start the blitter on a job and then have the 030 calculate the next job while the blitter is working. When the blitter is done the next job can be started instantly. With the 040 you would finish the job and then have to prepare the next in a synchronous manner. Hmmm. 1+1 != 3. You could have the 68040 do the graphical work then do the calculations then do the graphical work all in the same time that it took the blitter to do the the graphical work and the 68030 to do the calculations. In other words, the 68040 gets more work done in the same period of time. The other thing to consider is that the Amiga is a multitasking machine. Yes, the 040 might be able to render stuff faster than the blitter (this is a point which I feel really depends on the application), it has to stop doing other things and actually do the graphics. Consider what would happen if all the screen updates on the Amiga's workbench were done by CPU and not the blitter. Say I'm running a ray tracer in the background. If I move a window, or a cli window scrolls, updating the screen is going to steal CPU time from the ray tracer. Using the blitter, the display might not be updated as fast as it possibly could, but the CPU cost to do it is near nil because the blitter is doing the grunt work and thus the ray tracer doesn't get locked out as long. So the CPU has to stop and update the screen. What's the big deal? You have 2*N mips in your machine and N of those mips are only capable of bit manipulation, while the other N mips can be used for your ray tracer. Drop an 040 in the A3000 and you now have 3*N mips for calculations and you still only have have N mips for bit manipulations. N = 68030, of course. >So, the blitter is stealing from the faster chip, the 68030? Only in CHIP memory, of which there is a relatively small amount compared to FAST memory. Outside of things that HAVE to be in CHIP, the Amiga will use FAST memory first by default. Thus, most program code is loaded into FAST memory, and any number crunching type program (such as a ray tracer or spread sheet) will have its data storage in FAST memory as well. So it doesn't matter if the blitter is stealing cycles from the CPU's access to CHIP memory. Assuming you have 1 meg. Amiga. When you exand the Amiga to 1 meg. is 512K chip RAM and 512 FAST ram? Again, this depends on the application. For general usage, I'd much rather have the blitter used as it is now. It helps the system AS A WHOLE run faster. Now, I'm no multimedia guy, but for some apps I can see you would want to run an 040 balls out for extra rendering speed. That's a choice the designed of the software will have to make. Are people still writing directly to the hardware on the Amiga? Dedicated graphics hardware is nice but if all your software depends on specific hardware then you are not going to be able to take advantage of future advances. If you think the 68040 is fast wait until MIPS/Compaq/Microsoft drop their R4000 bomb(looks like next year). It's going to be almost three times faster than the 68040. On the Amiga that's N mips dedicated to graphics and 9*N mips dedicated to calculations. -Mike