dirk@altger.UUCP (dirk) (12/28/88)
I've been reading this newsgroup for a while now but I never saw the following question: Where did the 384K go ? If you install 2MB on a Compaq 386 you'll get 640K conventional memory and 1024K extended memory == 1664K. When booting 386/ix it reports 1703936 Bytes of real memory. So, where are they ? Some people told me that these 384K are called shadow RAM and placed just behind the 384K conventional memory gap from 0xa0000 - 0xfffff. Others told me that this memory is mirrored anywhere far away in extended memory. On a Chips+Tech chipset I saw an option to enable shadow memory by 16K page increments. So, where does the memory live, I think it can not be a problem to enable it and use it with 386/ix by patching the memory scan function (scanmem) in os.o. Probably it is just one more gap to cover. cu, dirk :-)
dave@pmafire.UUCP (Dave Remien) (01/01/89)
In article <1263@altger.UUCP> dirk@altger.UUCP (dirk) writes: >I've been reading this newsgroup for a while now but I never saw the =>following question: => => Where did the 384K go ? => =>If you install 2MB on a Compaq 386 you'll get 640K conventional memory =>and 1024K extended memory == 1664K. When booting 386/ix it reports =>1703936 Bytes of real memory. So, where are they ? Two of the three '386 machines I work on (Bell Tech and Mylex) have the 3.375 megs of memory above 640K start at 0x100000 (1 meg), and continue to 0x440000 (4.375 megs). The other, a FORTRON, loses the 384K because it can't remap the memory to start at 1 meg. It's actually not available, because that area is mapped by hardware to ROM and video RAM :-(. => =>So, where does the memory live, I think it can not be a problem to =>enable it and use it with 386/ix by patching the memory scan =>function (scanmem) in os.o. Probably it is just one more gap to cover. Just make sure that accessing that area doesn't get you into ROM or video. Availability seems to depend on how they set up the (hardware) address decoding. => =>cu, =>dirk :-) -- Dave Remien - WINCO Computer Engineering Group (only somewhat confused, now) Work - 208-526-3523 Home - 208-524-1906 UUCP Path: ...!bigtex!pmafire!dave
chasm@killer.DALLAS.TX.US (Charles Marslett) (01/03/89)
In article <1263@altger.UUCP>, dirk@altger.UUCP (dirk) writes: > I've been reading this newsgroup for a while now but I never saw the > following question: > > Where did the 384K go ? > > If you install 2MB on a Compaq 386 you'll get 640K conventional memory > and 1024K extended memory == 1664K. When booting 386/ix it reports > 1703936 Bytes of real memory. So, where are they ? The 384K of RAM that disappeared seems to be lurking at 0xE00000 (if I remem- ber correctly) as normal RAM. It can also be enabled with some granularity (16K or perhaps 64K) in the 0x00A000-0x00FFFF range. If you do not find it at 0xE00000-0xE5FFFF, let me know and I will fish out the utility I wrote to scan protected memory for such lumps of RAM. > cu, > dirk :-) =========================================================================== Charles Marslett STB Systems, Inc. <== Apply all standard disclaimers Wordmark Systems <== No disclaimers required -- that's just me chasm@killer.dallas.tx.us
james@bigtex.cactus.org (James Van Artsdalen) (01/03/89)
In <1263@altger.UUCP>, dirk@altger.UUCP (dirk) wrote: > Where did the 384K go ? > If you install 2MB on a Compaq 386 you'll get 640K conventional memory > and 1024K extended memory == 1664K. When booting 386/ix it reports > 1703936 Bytes of real memory. So, where are they ? Not all motherboard hardware supports mapping the "missing" 384K into the extended memory space. Some can map that 384K to the 1meg mark, but only if there is no other memory at the 1meg address. It's just a fact of life: too many chipset designers have a Mess-DOS mindset. I should point out that shadow RAM *is* a tremendous win under DOS... > [...] On a Chips+Tech chipset I saw an option to enable shadow > memory by 16K page increments. 386/ix is probably only using the 0-640K and > 1meg memory. A clever trick would be to enable all of the shadow memory possible in read/write mode and use it too, meaning you'd lose only the memory used by the video display and any memory mapped devices. -- James R. Van Artsdalen james@bigtex.cactus.org "Live Free or Die" DCC Corporation 9505 Arboretum Blvd Austin TX 78759 512-338-8789