Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!microsoft!davidds From: davidds@microsoft.UUCP (David D'SOUZA) Newsgroups: comp.windows.ms Subject: Re: Severe performance degradation with 386 enhanced mode, any tips? Message-ID: <70249@microsoft.UUCP> Date: 27 Jan 91 23:15:21 GMT References: <1991Jan16.224240.14201@news.iastate.edu> <1991Jan17.234310.6393@mintaka.lcs.mit.edu> <1991Jan20.183318.21088@vpnet.chi.il.us> Reply-To: davidds@microsoft.UUCP (David D'SOUZA) Organization: Microsoft Corp., Redmond WA Lines: 40 >In article <1991Jan17.234310.6393@mintaka.lcs.mit.edu> mikew@charm.LCS.MIT.EDU (Michael B. Williams) writes: >>A few of us out here are experiencing the same problem, but no one has >>yet suggested a solution that works. My NEC Powermate 386SX gives the >>following SI times (values are approximate): >> >>Computing Index >> From DOS (or Standard mode window): 15.2 >> From 386 mode: 4.6 Windows Enhanced mode uses 32 bit code. All memory accesses need to be 32 bits wide. On 386 machines, motherboard memory fetches can be done 32 bits at a time. Expansion memory is usually added to the mother board in which case you have 32 bit access to the new memory. Some, such as Compaq, have a dedicated memory expansion slot which also allows memory to be fetched 32 bits at a time. However, if you add more memory to your 386 using old style cards which plug into the AT style slots, you are hosed. This memory can only be accessed 16 bits at a time (the hardware does this automatically). Thus, it takes twice as long for the processor to fetch 32 bits from here. You could even incur wait states between fetches making things even slower. Real and standard mode just use 16 bit code and all memory fetches need only be 16 bits wide so you don't really notice the slow memory. Most dos apps are also 16 bit apps so once again, you don't see performance problems. When you run any 32 bit app, IF IT RESIDES IN THE SLOW MEMORY, it will also experience a slow down. Some 32 bit apps end up loading in mother board 32 bit memory and only data ends up being stored in the slower memory. So you don't notice a major slow down. Windows, due to its virtual memory, could end up in any portion of physical memory and even moves around, thus, tends to be more susceptable to slow memory problems. -Dave