Operating Systems
COMP 3430 Guderian
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I/O devices
What kinds of I/O devices are currently attached to your system? State whether this device is ¡°internal¡± or ¡°external¡±.
Pseudo devices
Pseudo devices
¡°Fake¡± devices.
Pseudo devices
¡°Fake¡± devices.
Entries in the device tree, no real device behind them.
Pseudo devices
¡°Fake¡± devices.
Entries in the device tree, no real device behind them.
What is it instead of an actual device?
Pseudo devices
¡°Fake¡± devices.
Entries in the device tree, no real device behind them.
What is it instead of an actual device?
Examples: /dev/zero, /dev/null, /dev/random
Block devices
Block devices
Entries in device tree backed by a real device.
Block devices
Entries in device tree backed by a real device. Reading and writing by blocks (more later).
Block devices
Entries in device tree backed by a real device. Reading and writing by blocks (more later).
Atomic units > 1 byte.
Block devices
Entries in device tree backed by a real device. Reading and writing by blocks (more later).
Atomic units > 1 byte. Random access.
Block devices
Entries in device tree backed by a real device. Reading and writing by blocks (more later).
Atomic units > 1 byte.
Random access.
Examples: /dev/sda, dev/nvme0n1
Just a taste of block
More next week, and assignment 4…
Character devices
Character devices
Entries in device tree backed by a real device.
Character devices
Entries in device tree backed by a real device. Reading and writing by characters.
Character devices
Entries in device tree backed by a real device. Reading and writing by characters.
Usually 1 byte at a time.
Character devices
Entries in device tree backed by a real device. Reading and writing by characters.
Usually 1 byte at a time. Sequential streaming access.
Character devices
Entries in device tree backed by a real device. Reading and writing by characters.
Usually 1 byte at a time.
Sequential streaming access.
Examples: /dev/random, /dev/snd/*, /dev/input/mouse0
Reading and writing
Reading and writing
Devices that are read/write.
Reading and writing
Devices that are read/write. Devices that are read-only.
Reading and writing
Devices that are read/write. Devices that are read-only. Devices that are write-only.
Organizing devices
Group the devices we listed into:
Organizing devices
Group the devices we listed into: Pseudo, character, block
Organizing devices
Group the devices we listed into:
Pseudo, character, block Read/write, read-only, write-only.
Talking to devices
We can read one byte at a time … there¡¯s got to be a better way …
Talking to devices
We can read one byte at a time … there¡¯s got to be a better way … That¡¯s what a driver is
Software communicates with hardware with hardware support.
Software communicates with hardware with hardware support.
Operating systems hide device details from software.
Software communicates with hardware with hardware support.
Operating systems hide device details from software.
Abstraction over devices.
Software communicates with hardware with hardware support.
Operating systems hide device details from software.
Abstraction over devices. Device drivers!
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