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A short class with Sarah and her students. The other ways are under More.
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Today we're going to discuss I/O commands. Can anyone explain why I/O commands are necessary?
I think they're needed so the CPU can communicate with other devices like printers and disks.
Exactly! Now, what would happen if the CPU didn't have a way to check if an I/O device was ready?
It would keep waiting unnecessarily and waste time.
Right! This inefficiency is why programmed I/O is so important. We will dive deeper into this shortly.
Remember, the main goal of I/O commands is to facilitate smooth communication without keeping the CPU stuck.
Now, let's break down the different types of I/O commands. Can anyone name them?
Controlling, testing, and read/write commands.
Correct! Let's discuss controlling commands first. What do they do?
They initiate actions in the I/O devices, like getting a printer to start printing.
Good! Now, could you describe what test commands do?
They check the status of the devices to see if they're ready.
Precisely! Testing ensures no conflicts occur when reading or writing data.
Now, let’s focus on addressing I/O devices. What can you tell me about the importance of addressing?
It's important so each device can be uniquely identified.
Exactly! Without unique addresses, the CPU wouldn't know which device it is communicating with.
How do we map I/O devices?
Great question! There are two main types: memory-mapped I/O and isolated I/O. Can anyone explain the difference?
In memory-mapped I/O, devices share the same address space as memory, while isolated I/O has separate spaces for memory and devices.
Correct again! This impacts the CPU's ability to access devices efficiently.
A method by which the CPU manages I/O operations by continuously checking the status of a device until it is ready for a data transfer. In this case, the CPU is actively involved in monitoring the status bit set by the I/O module, indicating readiness.
The CPU must identify the I/O module through unique addresses. Control commands are essential for initiating I/O operations, directing devices to perform tasks like reading or writing data. Commands fall into three categories: controlling, testing, and data transfer commands (read/write).
The addressing of I/O devices follows similar principles to memory addresses. Unique coding is necessary to prevent conflicts between devices and to enable the CPU to address them effectively.
There are two types of I/O mapping:
In this scheme, I/O devices share the same address space as the memory. Here, some memory addresses are reserved for I/O, allowing the CPU to use standard memory instructions for I/O operations.
This system uses a different address space for I/O devices, allowing for separate memory addressing for both memory and I/O. A control signal (IO/M̅) helps differentiate between memory and I/O addresses, enabling efficient communication.
By addressing these points, the section emphasizes the fundamental design choices in computer architecture regarding I/O management.
Polling the devices makes the CPU upset, wasting cycles it cannot forget.
In contrast, using control commands is like a teacher starting a lesson only when all students are settled.
Remember 'C-T-R' for Control commands, Test commands, and Read/Write commands to know all I/O command categories.
'MIME' for Memory and I/O Mapping Explained to help recall the two types of I/O mapping.
Term
What is programmed I/O?
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Term
What distinguishes memory-mapped I/O from isolated I/O?
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Instructions that enable the CPU to communicate with input/output devices.
A method where the CPU actively checks for device readiness to transfer data.
A scheme where the same address space is shared by both memory and I/O devices.
A system where I/O devices have a separate address space distinct from memory.
Commands that manipulate the state and operation of I/O devices.
This section explains the categories of I/O commands, highlighting the differences between programmed I/O, memory mapped I/O, and isolated I/O in data transfer.
The section details the steps involved in I/O operations, addressing the inefficiencies of polling, the roles of addressing schemes, and the distinction between different types of I/O mapping. It emphasizes the importance of control commands related to I/O operations.
In this section, we explore I/O commands' vital role in facilitating communication between the CPU and external devices. The necessity arises from the inefficiency of polling, where the CPU frequently checks the status of I/O devices, wasting time when it could be performing other tasks.
By addressing these points, the section emphasizes the fundamental design choices in computer architecture regarding I/O management.