Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!milton!sumax!thebes!amc-gw!jwbirdsa From: jwbirdsa@amc.com (James Birdsall) Newsgroups: comp.sys.ibm.pc Subject: Re: Command.com in ramdisk Message-ID: <1991Apr24.220908.17757@amc.com> Date: 24 Apr 91 22:09:08 GMT References: <1991Apr12.192526.23566@rodan.acs.syr.edu> <34067@ccicpg.UUCP> Reply-To: jwbirdsa@europa.amc.com (James Birdsall) Organization: Applied Microsystems, Redmond, WA Lines: 37 In article <34067@ccicpg.UUCP> mhr@ccicpg.UUCP (MHR {who?}) writes: >Whoa, hold on a moment there. > >The upper 384k of the first megabyte of memory on a PC _is_ EMS memory. >Why would anyone want to go out and get an EMS emulator whic requires >XMS (extended memory spec) memory when they already have the EMS they >need? Hold on yourself. The parts of this which aren't incorrect are meaningless. There are two 384K's wandering around. The high 384K of the first megabyte of address _space_ is used for video RAM, system ROM, the EMS page frame, etc. But if the motherboard uses 1M chips, there's an "extra" 384K of physical memory which can't just be dumped directly into the address space, the way the low 640K can. So, what happens to this extra 384K? Depending on the motherboard, it may be: 1) inaccessible 2) used to shadow ROMs 3) mapped just above the 1M line as extended memory 4) mapped elsewhere above 1M as extended memory 5) turned into expanded memory (EMS) via hardware on the motherboard 6) used for proprietary ramdisks, disk caches, etc. For example, the Compaq 306/20e does a combination of 2 and 4: it uses some of the memory to shadow the system and video ROMs, and maps the rest just below the 16M line as extended memory. It sounds like the original questioner has a motherboard that does at least 3 or 4 -- uses the memory to provide extended memory -- and is looking for something useful to do with it. -- James W. Birdsall WORK: jwbirdsa@amc.com {uunet,uw-coco}!amc-gw!jwbirdsa HOME: {uunet,uw-coco}!amc-gw!picarefy!jwbirdsa OTHER: 71261.1731@compuserve.com ================== Kitten: a small homicidal muffin on legs. ================== =========== "For it is the doom of men that they forget." -- Merlin ===========