Path: utzoo!attcan!ncrcan!ziebmef!stephen From: stephen@ziebmef.uucp (Stephen M. Dunn) Newsgroups: comp.sys.ibm.pc Subject: Re: Extended Memory Summary: Extended/Expanded difference etc. Message-ID: <1989May22.164426.20279@ziebmef.uucp> Date: 22 May 89 20:44:25 GMT References: <1939@ucsfcca.ucsf.edu> <1319@westmark.UUCP> <18358@cup.portal.com> <13828@watdragon.waterloo.edu> Reply-To: stephen@ziebmef.UUCP (Stephen M. Dunn) Organization: Ziebmef Public Access Unix, Toronto, Ontario Lines: 47 In article <13828@watdragon.waterloo.edu> trgauchat@rose.waterloo.edu (Terry Gauchat) writes: $And what is the real difference between extended, expanded, LIM, etc. memory: $what programs can and can't use which... Expanded memory (LIM) is extra memory that is bank-switched in 16K chunks into a 64K area of the memory address space. You can therefore access 4 pages at a time. This can be done, with the appropriate hardware, on a PC/XT/AT or 386 machine. Extended memory is accessible only to 286 or better machines in protected mode. It is the memory that appears above the 1Mb barrier of the 8086/88. What programs can use which? Very few programs use extended memory; the reason is that a program has to be written specifically for a 286 or better machine to be able to use it, and a lot of programs are written for the lowest common denominator - the old 8088. As for expanded memory, many programs will use this. You'll have to check each one and see. $Also, particularly: What type, and how much, RAM can an AT in protected mode $use? What type? Well, I guess you could use expanded memory if you wanted to, but I think you're thinking of extended memory, as noted above. How much? I'm not certain of this, but I believe 286 protected-mode addresses are 24 bits wide, which would give you 16 Mb of accessible memory. $What's the difference between on board memory and bus (or other not on board $memory?) -- (ie: what specification, speed, max size, etc.) Some motherboards allow for on-board memory expansion (especially the newer boards). These ones will allow you to populate them with fast chips if you like. Off-board memory may or may not be as fast. If it's in an expansion slot with a full-size data bus (16 bits on a 286/386SX, 32 bits on a 386) you can probably get it to work at whatever speed you want. If it's not in a full-size slot, you're obviously going to suffer some kind of speed penalty (just like the 8088 does in comparison to the 8086). Most AT-clone boards these days seem to allow either 1 Mb or 4 Mb on-board, and usually allow you to use this as either extended or expanded memory (my Suntac board allows for 512K/640K/1M/2M/4M with memory in excess of 640K as either type of memory). Some AT boards allow even more memory. As for 386 boards, they usually allow lots of memory space on-board. -- ------------------------------------------------------------------------------- ! Stephen M. Dunn stephen@ziebmef.UUCP ! DISCLAIMER: Who'd ever ! ! Take off to the Great White North eh, ya hosehead ! claim such dumb ideas? ! -------------------------------------------------------------------------------