New answers tagged intel
1
Memory may not have been quite so much of an issue as people were
making it out to be. Keep in mind that the base version of the
Altair 8800 (kit price $439) shipped with a "1024 word" (by which they
mean byte) memory board populated with only 256 bytes of RAM. If you
were willing to work with less, and in particular design your computer
to use RAM more ...
1
"Flat model" is simply unsegmented linear address space (3.2.1).
https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3a-part-1-manual.pdf
This is processor's definition of flat model. And OS defines flat memory model, "tiny" memory model, as well.
(in my own experience, I never felt flatness in "...
0
I've not heard the phrase "real mode flat model", but it may be referring to the fact that real mode allows a memory manager to manage memory as a linear sequence of 65,536 16-byte paragraphs (of which 40,960 would be within the first 640K). A memory manager which rounds all allocations to multiples of 16 bytes can avoid the need for any kind of 32-bit ...
0
There's one other legacy mode. On a 286, Windows 3.1 (possibly Windows 3.0), has a 286 protected mode, where GlobalAlloc() and GlobalLock() are used to allocate and lock a large amount of memory returning a far pointer where the upper half is a selector value. This allocates and locks a set of 64KB blocks of memory, and incrementing a selector (segment ...
5
1) All software sees the full 20bit address space, since there is no distinction between kernel and user land.
2) Flat mode is simply all segment descriptors set to maximum length and base offset 0. This is not feasible in 16 bit protected mode (80286), but most 80386 operating systems will use this mode in protected mode. There are other alternatives ...
25
I’m assuming you’re asking about x86 processors, not the older 8-bit CPUs.
Real mode is always segmented, and everything (CPU, operating system, programs, even peripherals on the CPU bus) has access to all the system’s address space up to just over 1 MiB (1 MiB strictly before the 286). You can write programs without paying attention to segments, and you’ll ...
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