the MASM reference manual assumes that you are familiar with assembly language
the purpose of the manual is to provide syntax reference, not to teach assembly language
Is there something - even in principle - that starts something that END ends? If, then what?
yes - the program source text
text that appears after the END directive is ignored by the assembler
the END directive has an optional argument that is required for programs, but not for modules
that argument allows the programmer to specify the program entry point
SEGMENT: Does that define physical or logical segment? Looks like physical, because it doesn't take any indications of which kind of segment?
i guess i would say that a segment is a logical reference to a physical memory region
as far as the assembler is concerned, it's logical (assembly-time)
when the program is executed, the operating system maps it to a physical/virtual area of memory (run-time)
16-bit DOS programs ran on systems with 1 MB addressable memory
a segment was actually a physical region in memory
32-bit/64-bit windows programs run on systems that address much more memory
segments are mapped to virtual pages or groups of pages of memory
simply put, the assembler uses segments to handle various memory attributes,
and as a reference for generating numeric addresses
The type (program/data/BSS) seems to be defined only by its use - that is: which segment register is set to point to it?
that's a fair observation under 16-bit DOS
although, to assemble executable instructions, it must be a CODE type segment
under 32-bit windows, segments map to sections of memory that have specific security attributes
various sections may allow or dis-allow reads, writes, or code execution
and - different privilege levels may have different access rights
for example, user-mode programs have ring-3 access (refer to the intel manuals)
.CODE and .DATA are logical segment start markers?
.CONST, .DATA, .DATA?, .CODE, and .STACK are aliases or shortcuts, intended to save typing
in "old style" syntax, segments are "opened" with a SEGMENT directive and "closed" with an ENDS directive
the programmer may provide name, type, combine, class, and a couple other attributes to a segment
segments may not be nested
masm provides shortcuts to open a limited set of standardized program segments
when the shortcuts are used, opening one segment automatically closes any previously opened segment
The linker may consolidate them to the same (unseen, internal) segments depending on the type?
as mentioned, segments have a "combine" attribute that tells the linker how they may be combined
furthermore, segments may be assigned to "groups"
in which case, the programmer may reference a group of segments and the linker will make them contiguous
The next .data continues where the last .data left off?
yes
What it is that ASSUME DS:@data does (in the assembler's point of view)?
the ASSUME directive has many uses, actually
but, when used for segment registers, it tells the assembler which program segment is pointed to by a specific register
a programmer may load a value into a segment register by use of a few different instructions
in some cases, it may be loaded from a variable
the assember cannot know what the value is at assemble-time
the specific directive "ASSUME DS:@data" is used to tell the assembler that the DS register points to DGROUP
DGROUP is a group that includes constant, initialized data, and uninitialized code sections
at least, that's the behaviour in the most commonly used memory models
for 32-bit code - all segments are in the same 4 GB addressable space (flat model)
but, in 16-bit DOS world, there are numerous models - the most common are TINY and SMALL
you can look at the reference material (or google) for descriptions of MEDIUM, COMPACT, LARGE, HUGE models
What is procedure block (from the assembler's point of view)? What are they used for?
simple answer, PROC = subroutine :P
it's an individual block of code
not all PROC's are subroutines, because the main program code may be assembled as a PROC
I guess when the command prompt starts the program, the CS is set to the program's code segment, but what's in the other segment registers?
.EXE program headers have values that tell the operating system how to assign initial values to most segment registers (code, data, stack)
operation varies between DOS and windows
under win32, you can pretty much ignore segment registers
a "flat" memory model is used, and all segments essentially point to the same 4 GB of memory
16-bit .COM programs have all code, data, and stack within a single 64 KB segment (CS = DS = ES = SS)
although, you are allowed to access memory outside that segment at run-time
