OS Lecture 04 - Storage Structure

Storage Structure in Operating Systems | RAM, Firmware, Memory Hierarchy & Secondary Storage In this lecture, Prof. Mostafa Elhosseini, Professor of Smart Systems Engineering, explains the Storage Structure of a computer system and how data and instructions move through the different levels of memory and storage. The lecture begins with main memory (RAM)—why it is called random access, why it is volatile, and why every running program must first be loaded into memory before the CPU can execute it. It also distinguishes between DRAM, used for main memory, and SRAM, commonly used for cache. OS Lecture 03 - Storage Structu… OS Lecture 03 - Storage Structu… You will also learn how the computer starts from power-on through the bootstrap process, including POST, the bootloader, loading the operating system into RAM, and the role of firmware, ROM, EEPROM, and flash memory. OS Lecture 03 - Storage Structu… OS Lecture 03 - Storage Structu… The lecture then introduces the basic units of storage—bit, byte, and word—and explains how memory is organized as an array of addressed bytes. The roles of load and store operations are discussed to show how data moves between main memory and CPU registers. OS Lecture 03 - Storage Structu… OS Lecture 03 - Storage Structu… The Von Neumann architecture is presented to explain how instructions and data share the same memory path, why this can create a bottleneck, and how the CPU repeatedly performs the Fetch → Decode → Execute cycle. Important CPU registers such as PC, IR, AC, MAR, MBR, general-purpose registers, and FLAGS are also introduced. OS Lecture 03 - Storage Structu… OS Lecture 03 - Storage Structu… The lecture also discusses the IAS computer structure, showing how the ALU, program control unit, registers, memory, and I/O path are connected, before moving to secondary storage and explaining why RAM alone cannot hold all programs and data permanently. OS Lecture 03 - Storage Structu… OS Lecture 03 - Storage Structu… Finally, the lecture presents the memory/storage hierarchy, from the fastest and smallest storage closest to the CPU down to larger and slower nonvolatile storage: Registers → Cache → Main Memory → Secondary Storage → Tertiary Storage The central idea is the trade-off among speed, capacity, cost, and volatility. OS Lecture 03 - Storage Structu… OS Lecture 03 - Storage Structu… Topics covered: RAM and random access, DRAM vs. SRAM, volatile vs. nonvolatile memory, bootstrap program, firmware and EEPROM, bit/byte/word, storage units, memory addressing, load/store operations, Von Neumann architecture, Fetch–Decode–Execute cycle, CPU registers, IAS computer structure, secondary storage, HDD/SSD, tertiary storage, and the memory hierarchy. By the end of the lecture, students should have a clear mental model of where programs and data live, how the CPU accesses them, and why computer systems use several levels of storage instead of relying on one type of memory alone.