Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: Opinions and Cold Hard Facts Requested Message-ID: <20457@cbmvax.commodore.com> Date: 8 Apr 91 19:07:27 GMT References: Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 97 In article erk@americ.UUCP (Erick Parsons) writes: > o In order to fully utilize the potential of a 68030 accelarator... > one needs at least 256K of 32 Bit Static ram on board Probably much more memory than that. With 256K of RAM, you might get a bit of extra performance by putting the KickStart code into it. Bit in general, if you don't have 32 bit RAM for programs to run in, you're not going to get much speedup, except in programs specifically coded for a 68882 FPU. > o 32 bit microprocessors are kludgy on 16 bit busses like that > of the A500. Well, "less than optimal" is a better way of looking at it. All Motorola 32 bit CPUs are optimized for 32 bit buses, and actually run a little worse than the 16 bit CPUs on 16 bit buses. In both the 68020 and 68030, for example, the CPU prefetches 32 bits of instruction memory at a time. This is no loss and often a win on a 32 bit bus, but can be a loss on a 16 bit bus, since a 32 bit read always takes two memory cycles, and there's no guarantee the second word will actually be used. On-chip caches can more than make up for these inefficiencies, but out of 16 bit RAM, you can't get much beyond a 20% or so speedup in typical 68030 operations (benchmarks show a little more speedup) with both caches on. > ? What is in fact the minimum amount of 32 bit wide ram necessary > to make the 68030 a blazingly fast, efficient accelarator ? That depends on how much memory you normally use. If 1MB on an A500 is plenty, you can probably get by with 1MB of 32 bit RAM and see most of the potential acceleration you can get. I'm never happy with less than 4MB, which is for CAD, DTP, and programming use. Folks doing 3-D rendering need as much as they can get. > Is static ram preferable to Dynamic Ram ? In an ideal world, yes. Problem is, static takes up more room than dynamic and it's much more expensive. You're much better off with a meg or two of DRAM than 256K-512K of SRAM. > ? Is my 16 bit ram going to slow things down? I have a sizable > investment in ram to date (5 megs) Slow down relative to what? A 32 bit CPU will be running slower from 16 bit RAM than it would 32 bit RAM. However, if you're out of 32 bit RAM, it's better to have that 16 bit RAM available than nothing at all. Any good accelerator setup will organize system memory lists so that the 32 bit RAM is used before the 16 bit RAM. > ? Do these accelarators use the same simm memory expansion modules > that other expansion boards use ? i.e. 1M x 8, and is the fact that > it is 80ns access time a detriment to burst mode caching ? Some use SIMM, others don't. Some support burst, others don't. Systems that support burst generally require 4MB chunks of 32 bit RAM, non-burst systems may allow 1MB or 2MB upgrade increments. The A3000 actually supports 1MB upgrades and burst, up to 4MB, or 4MB upgrades and burst, up to 16MB. But it uses custom logic not generally available on accelerator add-ins. > ? Will I realize any significant increases in speed in general with > Caching disabled on a 33 MHZ '030' / 68882 / 512K 32Bit Static Ram ? > ? " Caching enabled ? You don't want caching disabled with that little bit of Fast RAM. Make sure that the 68030 hardware allows caching of non-Chip 16 bit Fast RAM, or you'll not see much speedup in that system. > o A math co-processor will speedup dramatically CAD, 3D-rendering > programs and Spreadsheets that are floating point intensive. To some extent. Anything that uses the ieee math libraries will get an automatic speedup with an FPU present. Real floating point intensive programs, like renderers and the occasional CAD program, will come in versions with FPU code in-line, rather than via function calls, which can speed things up 25x or more, depending on the floating point component of the problem. > ? Will the addition of a 68882 co-pro. do anything for such things > as flight simulators and or simulations. Most games don't use floating point, but rather fast fixed point, if integers won't do. Any games that do use floating point probably use the Motorola FFP libraries, which don't get any FPU acceleration. However, since the FFP routines are in ROM, you can speed them up 2x-4x with by putting the ROM code into 32 bit RAM (via SetCPU or one of these CSA-type hardware hacks). > o There seem to be two versions (if not more) of '030's floating > around these days. There is the MMU and non MMU. Nope, there's only one 68030, it has an MMU. The only 68020 board out for Amigas with an MMU, to my knowledge, is the C= A2620. >Erick Parsons, Sacramento erick@sactoh0.sac.ca.us <-- Right off the freeway -- -- 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.