Is program in 8086 are relocatable?

Answer 1

Some are and some are not.

A model of a relacatable program is the DOS .COM file. As a disk file, this program is a binary image of what is loaded in memory. The segment registers are loaded by the operating system, and often were unchanged by the program during operation. It is possible, however, to request more memory from the operating system (or assume the memory is there) and use it, changing the segment registers as required.

The non-relocatable program is the .EXE file. In it, segment overrides are not filled in, and must be inserted by the operating system when the program is loaded. Such a file will run anywhere in memory that the operating system puts it, but it must be loaded by the operating system, and the image in memory is not the same as what is on disk.

Answer 2

Intel 8086/8088 program are sometimes relocatable or, more precisely, position independent, if they do not attempt to manipulate the segment registers. In this case, the OS can load the program anywhere in available memory on a 16 byte boundary, set the segment registers accordingly, and the program will run correctly. In this mode, however, the program only has access to four 64KB segments of memory.

It is also possible to be position independent and have access to more memory of the program takes the approach of biasing all segment manipulations to the initial values present at program startup.

Note that this discussion does not take into account the possibility that the load module format is, in itself, relocatable, requiring relocation by the loader. That is a third possibility.