Commodore PC Ms-Dos 3.2 User's Manual page 275

Unk: A Unker 203
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How Link Works
Link creates an executable file by concatenating a program's code
and data segments according to the instructions in the original
source files. These concatenated segments form an executable
image that is copied directly into memory when you run the pro
gram. The order and manner in which the linker copies segments
to the executable file defines the order and manner in which it
loads the segments into memory.
You can tell the linker how to link a program's segments by using
a SEGMENT directive to supply segment attributes, or by using
the GROUP directive to form segment groups. These directives
define group associations, classes, and align and combine types
that define the order and relative starting addresses of all seg
ments in a program. This information works in addition to any
information you supply through command line options.
The following sections explain the process that link uses to con
catenate segments and resolve references to items in memory.
Alignment of Segments
The linker uses a segment's align type to set the starting address
for the segment. The align types are byte, word, para, and page.
These types correspond to starting addresses at byte, word, para
graph, and page boundaries, representing addresses that are multi
ples of 1, 2, 16, and 256, respectively. The default align type is
para.
When the linker encounters a segment, it checks the align type
before copying the segment to the executable file. If the align
type is word, para, or page, the linker checks the executable
image to see if the last byte copied ends at an appropriate boun
dary. If it doesn't, link pads the image with extra null bytes.
Frame Number
The linker computes a starting address for each segment in a pro
gram. The starting address is based on a segment's align type and
on the size of the segments already copied to the executable file.
The address consists of an offset and a canonical frame number,
which specifies the address of the first paragraph in memory that
contains one or more bytes of the segment. A frame number is
always a multiple of 16 (a paragraph address), and the oflfeet is the
number of bytes from the start of the paragraph to the first byte
in the segment. For byte and word align types, the offset may be
nonzero, but the oflfeet is always zero for para and page align
types.
How link aligns
segments
Segment starting
addresses