Questions and Answers
This controller is usually located on the motherboard, or may be added with a ______ card.
PCIe
Controllers usually expose a set of control ______ to the OS to check their status and trigger operations.
registers
There are two main communication mechanisms for device ______.
controllers
Most architectures map device control registers into the physical address ______.
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Programs can then read from/write to these ports with special ______, available only in supervisor mode.
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I/O devices are physical devices that enable interactions with the ______ world
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Block devices store information that can be accessed later on, while character devices do not keep any ______ to be accessed later on.
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Examples of block devices include hard drives (HDD) and solid-state drives (SSD), while examples of character devices include ______ and keyboards.
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From an electrical engineer’s perspective, I/O devices are a set of chips and mechanical parts that perform ______.
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Devices usually have a hardware ______ that is used to interface with the rest of the computer.
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Study Notes
I/O Devices
- I/O devices are physical devices that enable interactions with the "outside" world, allowing computer systems to communicate outside the CPU-memory world.
- They can be classified as:
- Block devices that work with fixed-size blocks of information, addressable and accessible independently, used for storing information (e.g., hard drives, solid-state drives, magnetic tapes).
- Character devices that work with streams of characters, not addressable, and usually do not keep any information to be accessed later on (e.g., printers, keyboards/mice, terminals).
Device Controllers
- Devices usually have a hardware controller that interfaces with the rest of the computer, usually located on the motherboard or added with a PCIe card.
- Controllers expose a set of control registers to the OS to check their status and trigger operations.
- Controllers implement an interface specification (e.g., USB, SATA) to control devices in a standard way, detailing communication protocols between devices and the system.
- Controllers may also implement features like error checking/correction, replication, compression, encryption, wear leveling, virtual address translation, etc.
Communication With Devices
- There are two main communication mechanisms for device controllers:
- Device ports: each device control register is assigned a port number, allowing programs to read from/write to these ports with special instructions in supervisor mode.
- Memory-mapped devices: device control registers are mapped into the physical address space, protected as supervisor only, allowing the OS to use regular memory operations to interact with devices.
Bandwidths of Various Devices
- Keyboard: 10 B/s
- Mouse: 100 B/s
- Bluetooth 5 BLE: 256 KB/s
- 802.11n Wireless: 37.5 MB/s
- USB 2.0: 60 MB/s
- Gigabit Ethernet: 125 MB/s
- SATA 3 HDD: 600 MB/s
- USB 3.0: 625 MB/s
- PCIe 3.0 (single lane): 985 MB/s
- 802.11ax Wireless: 1.25 GB/s
- PCIe 5.0 nVME SSD (read): 14 GB/s
- USB 4.0: 5 GB/s
- PCIe 6.0: 126 GB/s
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Description
This chapter covers the basics of input-output devices, interrupts, and their role in operating systems and system software.
