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A short class with Sarah and her students. The other ways are under More.
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Let's start with programmed I/O. This involves the CPU requesting I/O operations and then checking the device's status repeatedly. Why do you think this might be inefficient?
Because the CPU is just waiting and can't do anything else!
Exactly! We call this 'polling.' The CPU wastes time waiting for a device to be ready for data transfer. Instead, what could be done to avoid this?
Maybe using interrupts so the device can notify the CPU?
That's a valid point! Polling leads to inefficiency while interrupts can signal the CPU when a device is ready, reducing wasted cycles.
To remember polling, think of it as the CPU doing repetitive check-ups—like waiting for your turn at a busy restaurant!
Now that we understand programmed I/O, let's talk about how we address devices. Why is it important to have unique addresses for each I/O device?
So that the CPU can communicate with the right device when performing operations!
Correct! Each device needs a unique identifier, similar to an address in real life. Can anyone tell me what kind of commands we might use for I/O operations?
We have to issue control commands and maybe read/write commands!
Exactly! Control commands initiate operations, while read/write commands handle the data transfer. Remember, these commands fall into categories: Control, Test, and Read/Write.
To recall the command types, think of ‘CTR’—Control, Test, and Read/Write—like a triplet team handling all I/O tasks!
Now, let’s differentiate between memory-mapped I/O and isolated I/O. Who can explain the difference?
In memory-mapped I/O, the same address space is shared between memory and I/O devices.
Correct! And what about isolated I/O?
In isolated I/O, the memory space and I/O space are different.
Exactly! In isolated I/O, there’s a separate control signal to identify if we're dealing with memory or I/O. Remember, isolated I/O can handle more devices due to its dedicated addressing—think of it as having separate highways for traffic.
Let’s put our knowledge to the test! Imagine you need to send a document to a printer using I/O commands. What steps would you take?
First, I would check if the printer is ready using the status command.
Great start! What’s next?
Then, I would send the data using the OUT command to the printer address.
Awesome! And after sending, how would you confirm successful transmission?
I would read the status again to ensure the print job is completed.
Perfect! This sequence demonstrates the full cycle of programmed I/O in action—keep this flow in mind as it can help you remember the process!
The section introduces programmed I/O, where the CPU requests I/O operations, and the I/O module checks device status. It emphasizes that I/O modules do not interrupt the CPU directly; instead, the CPU polls the device to check if it is ready for data transfer.
To facilitate I/O operations, certain commands must be issued to manage devices, including reading and writing data. Specifically, it outlines the need for addressing schemes to identify devices uniquely, which are delivered as a binary stream (0s and 1s). Control commands are also necessary to initiate operations on devices like printers and hard disks. The control commands can be categorized into three groups: Control, Test, and Read/Write.
The two addressing schemes discussed are:
Where I/O devices share the same address space as memory. This method allows for direct memory instructions to perform I/O operations.
In this scheme, separate address spaces exist for memory and I/O devices. The CPU uses control signals to determine whether the address is for memory or an I/O device, allowing for additional I/O devices to be connected.
The section concludes by explaining that the addressing scheme and commands are essential for operational efficiency in handling I/O operations.
Polling is like watching the clock, waiting for your turn to talk!
Imagine a librarian who must continuously check if a book is returned (polling) rather than being notified when it’s ready. That librarian would miss out on organizing the library while she waits!
Recall the command types as CTR: Control, Test, Read/Write.
Remember the addressing types with IM for Isolated Memory and MM for Memory-Mapped.
Term
What is Polling in I/O operations?
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Term
Explain Memory-Mapped I/O.
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Term
Control Commands in I/O.
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A method where the CPU continuously checks the status of an I/O device until it's ready for data transfer.
The repeated checking of a device's status by the CPU.
Instructions issued to manage the operation of I/O devices.
An addressing scheme where I/O devices share the same address space as the system memory.
An addressing method where memory and I/O devices have separate address spaces.
This section discusses the mechanisms and commands used for Input/Output (I/O) operations in computer processing, focusing on programmed I/O and different addressing schemes.
The section covers the basics of programmed I/O, where the CPU continuously polls device status. It explains the need for unique device addresses, the types of I/O commands, and distinguishes between memory-mapped I/O and isolated I/O. The importance of proper I/O addressing and control commands is also discussed.
This section provides insights into the special commands used for Input/Output (I/O) operations within computer systems. Initially, it discusses the challenges faced by CPUs when executing I/O operations, particularly the problem of polling. Polling requires the CPU to wait and check device readiness repeatedly, which can waste CPU cycles.
The section introduces programmed I/O, where the CPU requests I/O operations, and the I/O module checks device status. It emphasizes that I/O modules do not interrupt the CPU directly; instead, the CPU polls the device to check if it is ready for data transfer.
To facilitate I/O operations, certain commands must be issued to manage devices, including reading and writing data. Specifically, it outlines the need for addressing schemes to identify devices uniquely, which are delivered as a binary stream (0s and 1s). Control commands are also necessary to initiate operations on devices like printers and hard disks. The control commands can be categorized into three groups: Control, Test, and Read/Write.
The two addressing schemes discussed are:
The section concludes by explaining that the addressing scheme and commands are essential for operational efficiency in handling I/O operations.