1.1. Computer Organization and Architecture: A Pedagogical Aspect

In this lecture we begin our discussion with the module Memory System. The first unit of this module deals with the Basics of Memory and Cache.

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After learning this unit you should be able to illustrate the principle characteristics of a memory system. You should be able to analyze the module a memory module to indicate the size of the address bus, the data bus and also the memory organization basically. You should be able to describe the hierarchical organization of memory composed of registers, cache, main memory, magnetic disks, magnetic tapes etcetera.

This chunk introduces the concept of memory systems in computers. It outlines that the lecture will focus on memory systems and cache, which are critical to understand computer architecture. Key learning outcomes include understanding memory organization and being able to identify different types of memory, such as registers and various storage devices.

Think of a computer's memory system like a library. Just like a library has different sections, books, and storage methods, a computer's memory organizes data in various structures like registers (similar to books in a reading room), cache (like quick references), and disks (like storerooms).

Memory is broadly classified into two categories: Inboard memory and Outboard memory. Also, we also have offline storage which are basically bulk storage devices. So, what is inboard memory? Inboard memory are those memory units which are directly plugged into the motherboard of the computer. So, we have processor registers, cache memory, main memory; those are within on the motherboard of the computer itself, either on the processor or on the motherboard. Output memory on the other hand like magnetic disks or hard disks, optical disks etcetera are outboard memory, are not on the motherboard, are not plugged on the motherboard on the of the computer.

This chunk explains the classification of memory into inboard and outboard types. Inboard memory refers to memory components like registers and cache that are directly integrated into the computer motherboard. Outboard memory refers to storage devices that are not directly on the motherboard, such as hard disks and USB drives. Understanding this distinction is crucial as it affects how data is accessed and processed in computers.

Imagine a kitchen where inboard memory is like your pantry filled with essentials for cooking (processor registers and cache), while outboard memory is like a storage shed outside the kitchen holding bulk supplies (hard drives and USBs). The pantry allows for quick access and use, while the shed has more space but requires extra steps to access.

Now we will go on through a few basic definitions and terminologies which characterize memory. The first of them is capacity of a memory module. The capacity of a memory module is characterized in terms of the number of distinctly addressable memory locations and also the size of each of those locations. So, typically of the typically the size of a memory location is 1 byte for byte addressable memory. Although, there could be something called word addressable memory where I can address in higher more than a word, more than a byte; meaning that suppose if a word consists of 4 bytes, it and if it is word addressable I won’t be able to address and find out each byte within a word. But I will be able to access the byte the words themselves.

This chunk focuses on the definitions of memory capacity and addressing. Memory capacity refers to how much data the memory can hold, typically measured by the number of addressable locations and the size of each location. In byte-addressable memory, each memory location equals one byte. In contrast, word-addressable memory can group bytes, i.e., if a word consists of 4 bytes, you can only reference the word as a whole rather than its individual bytes.

Consider a bookshelf where each book represents a memory location. If each book contains one page (1 byte), it's straightforward to access each page. But if a book represents a set of 4 pages (word) and you can only borrow an entire book, you can’t just grab a single page from it without borrowing the whole book.

Memory data access methods. So, we have different types of memories and in these different types of memories there are various access methods. For example, we have sequential access memories in which data are stored as units called records and data are referenced in terms of its current location. So, there is a read-write head which is which is typically on the last location from which data was read or written to.

The second access type is direct access type of memories, hard disks that is magnetic disks are direct access types of memories. Each individual block has a unique address, access is by jumping to the vicinity of the block and then by doing a sequential search.

In this chunk, various methods for accessing memory are explained. Sequential access memory requires reading through data linearly until the desired information is found. This can be slow, as seen in magnetic tapes. In contrast, direct access memory, like hard disks, allows for quicker access since each block has a unique address, enabling more efficient locating of data. This difference is important for understanding how different types of memories perform.

Think about how you search for a book in a library. Sequential access is like looking at each shelf one by one, while direct access is like knowing the specific section and aisle (address) where the book is located, allowing you to go straight to it rather than checking each book individually.

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