Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!ncar!midway!clout!chinet!miroc!caw From: caw@miroc.Chi.IL.US (Christopher A. Wichura) Newsgroups: comp.sys.amiga.advocacy Subject: Re: Blitter vs. 040 (was: Computer Architecture question Message-ID: Date: 15 May 91 00:56:18 GMT References: <3310.tnews@templar.actrix.gen.nz> Lines: 58 In article melling@cs.psu.edu (Michael D Mellinger) writes: > >In article mykes@amiga0.SF-Bay.ORG (Mike Schwartz) writes: > >> Again, if you use the 040 to do graphics instead of a blitter, you lose the ability >> to do things in PARALLEL with the CPU. The 040 has a limited number of Cycles (yes >> gobs of them), and using them for rendering ovbiously gives you less of them for >> doing what work your applications do (or your multitasking OS...). > >What am I missing here? You have 15 mips in 1 second or you get 12 >mips the 030 + blitter. Does it really matter if they are running in >parallel as long as the bus isn't limiting you? 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. 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 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. >It will probably have a dozen more before the Amiga dies. In the mean >time, the blitter is on its way to becoming the bottleneck in the >system, if it already hasn't. 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. -=> CAW Christopher A. Wichura Multitasking. Just DO it. caw@miroc.chi.il.us (my amiga) ...the Amiga way... u12401@uicvm.uic.edu (school account)