There are many things being different between 16 bit asm programming and 32 bit asm programming.
* The introduction of 32 bit segment registers. (EAX, EBX, etc)
* A program written in native 32 bit Windows format is created in what is called FLAT memory model which has a single segment that contains both code and data. The programs must be run on a 386 or higher processor.
* Differing from earlier 16 bit code that used combined segment and offset addressing with a 64k segment limit, FLAT memory model works only in offsets and has a range of 4 gigabytes. This makes assembler easier to write and the code is generally a lot faster.
* All segment registers are automatically set to the same value with this memory model and this means that segment / offset addressing must NOT be used in 32 bit programs that run in 32 bit Windows.
* For programmers who have written code in DOS, a 32 bit Windows PE executable file is similar in some respects to a dos COM file, they have a single segment that can contain both code and data and they both work directly in offsets, neither use Segment / Offset addressing. The defaults in flat-model programs are NEAR code addressing and NEAR data addressing within the range of 4 gigabytes.
* The addition of FS and GS segment registers in 32 bit mode. The FS and GS segment registers are not normally used in application programs but are used in some instances by the operating system.
* 32 bit mode has introduced the concept of priority which helps for memory organization and isolation.
