🚀 go-pugleaf

mcc@wlv.imsd.contel.com (Merton Campbell Crockett) writes:

>This will seem like a terribly naive question to many of you--it does to
>me; however, I would like to understand the difference between extended and
>expanded memory.

>I'm sure part of my problem in understanding the documentation provided with
>my 80286 (home) and 80486 (office) systems is my background.  I am and have
>been a systems programmer on NCR Century series, DECSystem 10, PDP11 series,
>and VAX series computers.  And, with the exception of NCR all have memory
>management hardware managed by the various operating systems that I've used.

>In this environment, programs can be loaded anywhere in physical memory but
>from the program's perspective it's address space always begins at location
>0 in its logical address space.  (For the nit pickers, thats not entirely
>correct but will suffice for this discussion.)  In writing device drivers,
>I simply remap the buffers involved into the device drivers address space
>and either use programmed I/O to transfer the data or set the devices hard-
>ware registers to access the physical memory associated with the logical
>memory address of the buffer for a DMA operation.

>Now, I have this 80486 system with 4 Mbytes of memory.  I have MS-DOS 4.01
>as an operating system but it only seems to know how to deal with the first
>640 Kbytes of memory and the "device" address space between 640K and 1M bytes.
>To support the various devices and a 210 Mbyte disk, MS-DOS seems to load
>a significant number of system programs in memory significantly reducing
>the 640Kbytes it knows about--to the extent I have programs complaining about
>insufficient space to perform some of their operations.

>Now with the memory management logic in the 80486 chip it seems that there
>should be no problem loading these extensions to the operating system into
>the memory above 1 Mbyte and have them execute from there.  Or for that,
>load a program anywhere that it will fit and let it execute from there.

>Now, given the above do I want extended or expanded memory?  One memory schema
>allows me to map memory in 64Kbyte windows but doesn't really allow me to
>execute code from that segment--or do I have that wrong?  Some application
>software contains logic to utilize memory above 1 Mbyte--do I have to check
>out each program and compute how much space it will utilize to install the
>memory management software?

>I'm sooooo confused!

It *is* confusing.  I've explained the whole schpiel a million times to
my co-workers, without ever really feeling that any of it took.

Just get QEMM and let it do the dirty work...