Newsgroups: comp.sys.ibm.pc.hardware Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!snorkelwacker.mit.edu!ira.uka.de!fauern!NewsServ!!roell From: roell@informatik.tu-muenchen.de (Thomas Roell) Subject: Re: Mentor & Trident VGA cards - which one is the best ? In-Reply-To: roell@informatik.tu-muenchen.de's message of Wed, 10 Apr 1991 10: 09:31 GMT Message-ID: <1991Apr11.095521.26017@Informatik.TU-Muenchen.DE> Sender: news@Informatik.TU-Muenchen.DE Organization: Inst. fuer Informatik, Technische Univ. Muenchen, Germany References: <1991Apr3.071713.6290@fel.tno.nl> <3725@d75.UUCP> <1991Apr6.192215.29729@leland.Stanford.EDU> <1991Apr9.004129.20991@odin.corp.sgi.com> <1991Apr10.100931.27295@Informatik.TU-Muenchen.DE> Date: Thu, 11 Apr 1991 09:55:21 GMT Lines: 46 >Yes but the problem is ONLY with scrolling. Perhaps with some chaching tricks >the overhead could be reduced. For example with the ET4000 you have one >read operation followed by one write operation. This means the processor has >to wait for getting videomemory access. The ET4000 reads one line (32 bits) >at once and buffers it. But cause of the following write this buffer is once >again flushed. But the write will be buffered in a write-buffer internally. >If the TVGA8900 has the same architecture the sequenece of reads and writes >will make full use of such internal buffers. And if you read only small blocks >of data that fit into one line of the 386 cache there might be an additional >improvement. Concluding I assume that the overhead of the TVGA8900 of the >ET4000 in scrolling would be about 40 to 60%. All other operations shounld >have the same speed. Ok, I think this was a little bit to abstract, so lets fill in some numbers. Assume we do a simple bitblit, only 32bit words, all correctly aligned, no shift necessary. Under this assumptions a ET4000 makes about 1.7 MBytes/sec. This was measured on a 33MHz 386. Thus one movsl I used for blitting too about 78 cpu cycles. Thus the raw VGA accesses took about 74 cycles. Now to the TVGA8900. I assume that a read and a following write are as fast as for the ET4000, 74 cycles. But here we have first to buffer the stuff: 74 VGA read/write 4 movsl for buffering 5 storing the buffered data into memory 4 movsl for bltting from memroy into VGAs. 0 reading data from cache -- 87 cycles This means that the TVGA8900 is at least 12% slower. At an average I assume about 20% slower performance than the ET4000 is they have the same memory troughput. But if you really need speed, forget about VGA. Buy a 8514. Benchmarks: VGA 640x480x256 6600 xstones ET4000 VGA 1024x768x256 4800 xstones 8514 1024x768x256 26300 xstones WD9510 - Thomas -- _______________________________________________________________________________ E-Mail (domain): roell@lan.informatik.tu-muenchen.de UUCP (if above fails): roell@tumult.{uucp | informatik.tu-muenchen.de} famous last words: "diskspace - the final frontier..."