Professional Courses
Industry-relevant training in Business, Technology, and Design to help professionals and graduates upskill for real-world careers.
Categories
Interactive Games
Fun, engaging games to boost memory, math fluency, typing speed, and English skills—perfect for learners of all ages.
Typing
Memory
Math
English Adventures
Knowledge
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Understanding Polling
Unlock Audio Lesson
Today, we're going to discuss polling and how it affects the CPU's efficiency. Can anyone tell me what polling is?
Isn't it when the CPU checks if a device is ready repeatedly?
Exactly! Polling is where the CPU continuously checks the status of an I/O device. This can lead to CPU time being wasted. Why do you think that is?
Because while it's checking, it can't do anything else?
Exactly! So, polling can lead to inefficiencies. Hence, CPUs require a better way to manage I/O devices. Let's remember: 'Poll to know, but don’t commit to slow!' That's our first memory aid today.
Programmed I/O
Unlock Audio Lesson
Now that we understand polling, let’s talk about programmed I/O. What are the steps involved in conducting programmed I/O?
First, the CPU requests an I/O operation.
That's right! Then what happens after that request?
The I/O module performs the operation and sets the status bit accordingly.
Excellent! The CPU will then check this status bit until it is ready. Let's remember the step sequence: Request - Perform - Check.
Addressing I/O Devices
Unlock Audio Lesson
Next, we need to identify how I/O devices are addressed. What is important here?
Each device must have a unique address!
Right! Each I/O device must have a unique address, similar to memory addressing. Can anyone name the two main addressing schemes?
Memory-mapped I/O and isolated I/O!
Good! Memory-mapped I/O shares address space with general memory while isolated I/O keeps them separate. Now, which one allows for more devices to be connected?
Isolated I/O would allow more devices since it has separate address space.
Correct! Just remember: 'Isolated is spacious, while mappers are closer!' That's our next memory aid.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
In this section, we explore the concept of polling, where the CPU continuously checks the status of an I/O device, leading to wasted CPU time and inefficient processing. The section also covers programmed I/O and the addressing schemes necessary for I/O operations, including memory-mapped and isolated I/O.
Detailed
Problems with Polling
Polling is a method where the CPU repeatedly checks the status of an I/O device to determine if it is ready for data transfer. This leads to significant CPU time wastage as the processor cannot conduct other tasks while waiting. In programmed I/O, the CPU initiates an I/O operation and then continuously polls a status bit to see if the device is ready. This method does not allow the CPU to perform any other operations during polling, hence it is a less efficient use of resources.
Key concepts also include the need for addressing within I/O operations. Each I/O device must have a unique address for identification, and the I/O module must issue control commands to manage these operations effectively. The two main addressing schemes discussed are: 1) Memory-Mapped I/O, where the I/O devices share the same addressing space with memory, and 2) Isolated I/O, in which separate address spaces for memory and I/O devices are used, significantly increasing potential device connections. Both methods have their applications and situations where they are more advantageous than the other. Ultimately, programmed I/O requires effective communication between CPU and I/O devices through these established commands and addressing schemes.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
CPU Polling Problem
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, basically it is a sensing of status, then using the read write command, then transferring of data; this is the way that we are going to do, but here what is the problem that we have first? CPU needs to wait and poll, it is checking it continuously. So, it cannot do any other work. So, there is a wastage of CPU time.
Detailed Explanation
Polling is a method where the CPU continuously checks the status of an I/O device to see if it is ready for the next operation. This can be problematic because while the CPU is busy checking the status of devices, it cannot perform other tasks. This results in wasted CPU cycles, which could otherwise be used to execute other instructions or processes. Essentially, the CPU is sitting idle, waiting for a device to become ready, leading to inefficiency in resource usage.
Examples & Analogies
Imagine a waiter in a restaurant who keeps checking if a customer is done with their meal instead of attending to other tables. While the waiter is fixated on one customer, other customers might need service too. This can lead to delays and dissatisfaction among the patrons.
Programmed I/O Steps
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, basically this is now programmed I/O details now you just see these are the simple steps; first one CPU requests to I/O operation that in processor we have shown it, I/O module performs operation, then by looking into the state of the devices I/O module sets the status bit, CPU checks status bits periodically, I/O module does not inform CPU directly.
Detailed Explanation
Programmed I/O involves a sequence of steps where the CPU initiates an I/O operation. First, the CPU makes a request to the I/O module to perform a certain task. The I/O module then carries out the operation and sets a status bit in its register to indicate whether the operation is complete. The CPU must periodically check this status bit to determine if it can proceed with the next task. This method lacks direct communication between the I/O module and the CPU, which can lead to delays and further inefficiencies, as the CPU must wait for the status bit updates.
Examples & Analogies
Think of this like a person waiting for their turn in line to use a public restroom. They keep checking (polling) if the restroom is available, but the staff do not announce when it becomes free. So the person must keep looking back and forth, wasting time instead of doing other things.
I/O Commands and Addressing
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
Already I have mentioned that we need some commands I/O commands. So, first the issues for that I/O command is like that how to identify the module. So that means, we have to have device address so this is the one point how we are going to give the addresses of the I/O devices.
Detailed Explanation
In order to carry out operations with I/O devices, the CPU must communicate specific commands and know the addresses of those devices. Each I/O device is assigned a unique address that the CPU uses to send commands or requests. The addressing scheme ensures that when a command is issued, it reaches the correct device. Like memory addressing, I/O addressing is crucial for effective communication between the CPU and peripherals.
Examples & Analogies
Imagine sending letters to friends. Each friend has a unique address, just like each I/O device has a unique address. If you want to send a letter only to one friend, you must make sure you write their address correctly. Otherwise, the letter might be delivered to the wrong person. This is similar to how the CPU must ensure it sends commands to the correct I/O device.
Memory-Mapped I/O vs. Isolated I/O
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, in that particular case we are having two different ways of doing it. One is your memory mapped I/O and second one is your isolated I/O.
Detailed Explanation
There are two primary methods for interfacing I/O devices with the CPU: memory-mapped I/O and isolated I/O. In memory-mapped I/O, the same address space is shared between memory and I/O devices, allowing the CPU to use the same instructions for both. This means a command for reading from memory could also read from an I/O device if the address corresponds to one. In isolated I/O, memory and I/O devices have separate address spaces, meaning distinct instructions must be used to communicate with each. This separation can allow for more devices but requires different programming approaches.
Examples & Analogies
Consider how different departments communicate within a company. In a memory-mapped approach, all departments use the same meeting room (address space) for discussions, so communication is straightforward. However, in isolated I/O, each department has its own office rooms (separate address spaces) for discussions, necessitating special permission (different instructions) to meet.
Control Signals for Isolated I/O
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
To identify whatever addresses that we have put in this particular address bus. It is an address of a memory location or it is an address of an I/O devices. So, to identify these things so, we are going to use one more control signal.
Detailed Explanation
When using isolated I/O, it is crucial to have a method for distinguishing between memory addresses and I/O addresses. This is accomplished using a control signal, typically referred to as the IO/M signal. This signal indicates whether the address on the bus refers to an I/O device or a memory location. When the signal indicates I/O, the CPU knows to treat the address as an I/O command, whereas if the signal indicates memory, the CPU will treat it accordingly. This distinction is vital for correct data handling.
Examples & Analogies
Think of a person working in a library (CPU) who needs to decide whether to shelve a book (memory) or place a magazine in a display area (I/O device). The librarian uses specific signs (control signals) to differentiate between the two tasks, so they don't mistakenly place a book in the wrong section.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Polling: The process by which a CPU maintains checks on I/O device status.
-
Addressing: The unique identifiers assigned to I/O devices for operational reference.
-
Memory-Mapped I/O: An I/O addressing scheme using shared memory addresses.
-
Isolated I/O: An I/O addressing method with distinct address spaces for devices and memory.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
When a CPU checks if a printer is ready to print, it polls the printer's status bit continuously.
-
In memory-mapped I/O, the CPU uses the same memory addresses to communicate with both RAM and I/O devices.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
-
When polling starts to loom, CPU's in a waiting room.
📖 Fascinating Stories
-
Imagine a teacher waiting by the door to check if students are ready instead of teaching the rest of the class. That's similar to how polling works.
🧠 Other Memory Gems
-
P.A.S. - Polling, Addressing, Scheme. Remember the sequence of key concepts.
🎯 Super Acronyms
P.I.O. - Polling Is Overhead. To remember that polling has drawbacks.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Polling
Definition:
A method where the CPU repeatedly checks the status of an I/O device to determine readiness for data transfer.
-
Term: Programmed I/O
Definition:
A technique where the CPU directly controls I/O operations through a program, checking for the status of devices.
-
Term: Addressing Scheme
Definition:
The method used for assigning unique identifiers (addresses) to I/O devices.
-
Term: MemoryMapped I/O
Definition:
An addressing scheme where I/O device addresses overlap with memory addresses.
-
Term: Isolated I/O
Definition:
An addressing scheme where I/O devices have separate address spaces from memory.