Advanced Operating Systems - Spring 2009 Lecture 18 – March 25, 2009 Dan C. Marinescu Office: HEC 439 B. Office hours: M, Wd 3 – 4:30 PM. TA: Chen Yu Office: HEC 354. Office hours: M, Wd 1.00 – 3:00 PM. 1

Last, Current, Next Lecture Last time: Page replacement algorithms Today I/O subsystem Next time: File Systems 2

I/O Systems I/O Hardware Application I/O Interface Kernel I/O Subsystem Transforming I/O Requests to Hardware Operations Streams Performance

I/O Hardware Variety of I/O devices: storage networking graphics video scanners, phones,… Attributes of I/O devices Character-stream or block Sequential or random-access Sharable or dedicated Speed of operation Read-write, read only, or write only

I/O devices Connected using Controller (host adapter) Buses Ports I/O operations occur as result of privileged I/O instructions Devices have addresses, used by I/O instructions Memory-mapped I/O 5

Alphabet soup; busses and interface standards PCI (Peripheral Component Interconnect)  computer bus integrated circuit fitted on the fitted onto the motherboard itself, called a planar device expansion card that fits into a socket e.g., network, sound, and TV tuner cards, modems, extra ports such as USB or serial, and disk controllers. PCI video cards are available for supporting extra monitors and upgrading PCs that do not have any AGP or PCI express slots. AGP (Accelerated/Advanced Graphics Port  high-speed point-to-point channel for attaching graphics cards primarily for 3D graphics. AGP is being progressively phased out in favor of PCI Express. ATA (AT Attachment ) and ATAPI (AT Attachment Packet Interface)  interface standards for the connection of storage devices such as hard disk, solid-state drives, and CD-ROM drives. 6

More alphabet soup SCSI (Small Computer System Interface)  set of standards for physically connecting and transferring data between computers and peripheral devices such as hard disks and tape drives; it can connect a wide range of other devices, including scanners and CD drives. The SCSI standards define commands, protocols, and electrical and optical interfaces. USB (Universal Serial Bus)  serial bus standard; replaces many serial and parallel ports allows hot swapping; provides power to low-consumption devices, eliminating the need for an external power supply; allows many devices e.g., mice, keyboards, joysticks, scanners, digital cameras, PDAs, flash drives, external hard disks, to be used without requiring manufacturer -specific drivers to be installed,. 7

More alphabet soup IDE (Integrated Drive Electronics)  interface standard for connecting storage devices e.g., such as hard disks, solid-state drives, CD ROM drives; not just to the connector and interface definition, but also the drive controller is integrated into the drive, as opposed to a separate controller on or connected to the motherboard. The integrated controller presented the drive to the host computer as an array of 512-byte blocks with a relatively simple command interface. This relieved the software in the host computer of the chores of stepping the disk head arm, moving the head arm in and out, and so on. ISA (Industry Standard Architecture)  bus standard developed at IBM for the PC. In 1987, IBM replaced it with MCA (Micro Channel Architecture) in an effort to regain control of the PC architecture and the PC market. InfiniBand  point-to-point bidirectional serial link for connection of processors with high speed peripherals such as disks. 8

VIA (Virtual Interface Architecture) An abstract model of a user-level zero-copy network. created by Microsoft, Intel, and Compaq, the original VIA sought to standardize the interface for high-performance network technologies known as System Area Networks (SANs) the basis for InfiniBand. Networks are a shared resource. In traditional networks such as Ethernet, the network is protected by the kernel, which presents a tremendous performance bottleneck when latency is an issue. 9

Typical PC Bus Structure

Device I/O Port Locations on PCs (partial)

Polling versus Interrupts Polling  periodically checking the status of an I/O device Interrupt  deliver data or status information when status information immediately States of device ready busy error Alternatives Busy-wait cycle to wait for I/O from device Use interrupts

Interrupts: used for I/O and for exceptions CPU Interrupt-request line  triggered by I/O device Interrupt handler receives interrupts To mask an interrupt  ignore or delay some interrupts Interrupt vector to dispatch interrupt to correct handler Based on priority Some non-maskable