640K Base Memory

[Quaggoth]

Do PC's still operate off 640K base memory?? I would imagine if they do there would be no such thing as the "No Memory" beep code... anyway, Thanks in advance.

 

[kingbob]

I'm not sure but I think they do because I always see something about base memory when I boot up.

 

[Whitedog]

In a sense, yes... but once windows is stated, it does it's own thing with memory.

 

[alkemyst]

yeah old DOS items still keep us from instant on machines and alot of good stuff.

Bill Gates made it 640K because 666K would have been too obvious. 🙂

 

[CTho9305]

Originally posted by: Quaggoth
Do PC's still operate off 640K base memory?? I would imagine if they do there would be no such thing as the "No Memory" beep code... anyway, Thanks in advance.

that 640k is not on teh board. it is part of your ram. On really old machines (like a 486), you might have 4 MB ram, 640k of which DOS called "base memory".

 

[CQuinn]

The "No Memory" beep code... is there for when the board or CPU does not properly detect available RAM.
That can happen when your DIMMs are not seated properly, or if the module has failed.

All x86 compatible CPUs (AFAIK) still have the 640K Base (Acutally 1Meg Base) because they all start in
"real" mode, which is a limited running mode based on the legacy of the old 8086 CPUs. In real mode,
the CPU gives the first 640K of system memory to the OS and programs, and reserves another 384K for
itself. As old operating system became better, they could take advantage of parts of that reserved space;
called the High-memory area (HMA). There were ways to use more memory, but they usually involved
tricking the CPU into swapping sections of higher memory in and out of the HMA.

After the 80386 was introduced(1), CPUs could switch to "protected" mode, which gave them the ability
to directly address memory above the first Megabyte of RAM.

(1) Technically the 80286 could switch into protected mode, but it was not designed to switch back out
to real mode when it needed to.