Computer Architecture is the fifth chapter that has been added in the syllabus of Computer Science ICS-I (Intermediate Part-1). Today, Computer Science is widely used in almost 99% of the organizations and its importance cannot be neglected today. After the introduction of Computers, the business world changed forever. Almost 99% of the businesses today use Information Technology to ensure their departments run smoothly. Information Technology is widely used today in the core departments of all the organizations like Human Resources (HR) / Personnel, Finance, Budget and Security. In this chapter the student will learn about the Block diagram of computer (CPU, RAM, ROM, input/output, data bus, address bus, control bus and ports), Introduction to ALU, CU, main memory (RAM, ROM), input/output unit, bases and Registers, Program counter (PC), memory address register (MAR), memory buffer register (MBR), instruction register (IR), stack, accumulator, data register, data address register (DAR), Computer Operations i.e. Simple Machine Instructions format, instruction codes and Processing Machine Instructions (fetch-decode-execute), to understand the functionality of different types of software and Operating environment.