What is Computer Architecture?

Computer architecture is the design and organization of a computer’s core components and systems, defining how it processes instructions and manages data.

About x86 Toolchain

The following concept of a toolchain is applicable to the C and C++ programming languages:

• The primary function of a toolchain is to convert a program from a human-readable format into a machine-readable binary format.
• The toolchain concept is applicable to every programming language.
• All the tools in the toolchain are used in a chained format, where the output of one tool serves as the input to the next tool.
• The output of the final tool in the chain is the executable file.
• Once we obtain the executable file, we can load it into the microprocessor for execution.
• The following points about the toolchain are common to both C and C++ programming.
• Both of these languages are high-level, native programming languages.
• A native programming language interacts directly with the microprocessor.

Step 1

• Write the program using an editor.
• Save the file with the extension .c.
• Name the file, for example, hello.c.

Step 2

• Pass the file to the compiler.
• In this context, the compiler internally includes the preprocessor, compiler, and assembler.
• The output of the compiler is an .obj file in binary format.
• The .obj file is divided into three sections:
  1. Text – Contains the compiled instructions of the program in binary format.
  2. Data – Contains memory for global variables used in the program.
  3. Symbol Table – A table containing information about the symbols (variables) used in the program.

Step 3

• Pass the .obj file to the linker.
• The linker links our .obj file with other dependent .obj files.
• The linker creates an .exe file, which is the executable file.

Step 4

• The executable file created by the linker is stored on the hard disk.
• To execute the file, it must be loaded into RAM.
• The loader is responsible for loading the executable file into RAM.

Step 5

• The primary header is added to the .exe file.
• The primary header contains information about the executable file.

Step 6

• When the loader loads the file into RAM, it is considered a process.
• The process loaded into RAM is divided into three parts: Text, Data, and Stack.
  • Stack: Contains information about the functions written in the program.

Step 7

• The process is now loaded into RAM and divided into Text, Data, and Stack sections.
• RAM is not responsible for executing the process; the process is passed to the microprocessor.

Step 8

• The microprocessor has limited memory compared to RAM, so direct loading of text, data, and stack is not practical. Therefore, each section is divided into multiple segments.
  • The Text segment is copied into CS (Code Segment).
  • The Data segment is copied into DS (Data Segment).
  • The Stack segment is copied into SS (Stack Segment).
  • If these segments are full, the ES (Extra Segment) is used.
  • If the ES is also full, FS and GS are used (FS and GS do not have specific full forms).

Step 9

• Data from the segments is copied into the instruction queue.
• The instruction queue fetches one instruction at a time and forwards it for execution.
• The IP (Instruction Pointer) fetches one instruction at a time.

Step 10

• The instruction is forwarded to the ALU (Arithmetic Logic Unit) if it relates to an arithmetic operation; otherwise, it is forwarded to the CU (Control Unit).
• The FLAGS register indicates the internal status of the microprocessor.

Step 11

• The instruction is stored in the CPU registers.
• There are multiple CPU registers, each serving a specific purpose:
  1. AH, AL – Arithmetic / Accumulator Register
  2. BH, BL – Base Register
  3. CH, CL – Count Register
  4. DH, DL – Data Register
  5. SP – Stack Pointer
  6. BP – Base Pointer
  7. SI – Source Index
  8. DI – Destination Index
• The instruction is executed within these CPU registers.

Step 12

• The output of the instruction is forwarded to the operating system via the IDB (Internal Data Bus).
• The operating system displays the result on the screen.

Important Abbreviations and Full Forms

.obj – Object Code

.exe – Executable

PH – Primary Header

RAM – Random Access Memory

BIU – Bus Interface Unit

ECU – Execution Control Unit

IP – Instruction Pointer

RCU – Register Control Unit

EU – Execution Unit

BCU – Bus Control Unit

FSB – Front Side Bus