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: mykes@amiga0.SF-Bay.ORG's message of 14 May 91 00: 18:48 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: Tue, 14 May 1991 06:22:07 GMT Lines: 46 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? The custom chips in the Amiga can and often do cause the CPU to wait when it accessis CHIP RAM. If the blitter is running in NASTY mode, for example, it will steal every possible cycle from the CPU (on the CHIP BUS only). If you are using some of the higher resolution graphics modes (like 640x400x16 colors), the display hardware steals 100% of the CPU (and blitter) cycles except for horizontal and vertical retrace. The Amiga workbench is 640x200/400 x 2 planes, because it steals no cycles in this mode. So, the blitter is stealing from the faster chip, the 68030? Your question about graphics modes shows that you haven't learned much at all about the Amiga (RTFM, please). To get 640x400x4096 colors, you can use a single bitplane of 32,000 bytes, but your graphics mode is seriously limited (you have to do EVERYTHING with the copper). In HAM mode, you can't go 680 horizontal, but you can open 10 (96K each) 4096 (6 plane) 320x400 screens in 1Meg of CHIP RAM. The Amiga does support overscan, so you can get hirhger resolutions (I'm using 704x484). Yeah, the Amiga has a dozen different graphics modes. That's nice. 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. The Amiga 500 doesn't even ship with 1Meg of RAM (the 500P does), and it is fully able to run the entire Amiga OS (multitasking and all), and virtually all applications for the Amiga (except the very few that require 1+ memory). Yes, so what! Are we bragging about how few paper clips we wasted? Memory is cheap. We just bought 16MB of memory for $650 for our NeXT. Functionality is more important. On the NeXT we have an OS that supports 24 bit color, has memory protection, virtual memory, and does much more. -Mike