Wednesday, June 07, 2006 “Unix is user friendly … it’s just picky about it’s friends”. - Anonymous

§Course URL §Folder on indus \\indus\Common\cs381m05 §Read course policies on the website! CS 381 : Operating Systems

Some design issues I/O Space §Special IN/OUT instructions (use of assembly code) §Calling procedure adds overhead to I/O Memory mapped Con: l Uses up some memory space l Caching of device registers should not be done! l Multiple buses Pro l No extra protection needed to keep user processes from doing I/O

Unix §Initial project turned into multimillion dollar industry involving universities, government organizations, multinational corporations. §Late 1980s … l AT&T (System V) and UC, Berkeley, (BSD) incompatible versions l IEEE standard for UNIX POSIX (defines minimal system call interface)

Unix §A multi-user, time-sharing operating system. §It can have many users logged into a system simultaneously, each running many programs.

Unix §Command based interface §Al most all UNIX systems support a windowing system as well l X-Windows l Developed at MIT

§Linux l Underlying structure common to UNIX §Versions subsequent to MS-DOS included many advanced features taken from UNIX. §Our discussion shall apply to different versions/clones of UNIX like BSD, System V, Linux etc. (Sun Solaris has its own variant of UNIX).

Linux Linux availability across a wide spectrum of platforms Distributions implemented on 64-bit architecture processors. §Large enterprise servers §Medium sized and small servers, workstations §Desktops §Laptops §Small intelligent devices.

l IBM Linux-based wrist watch.

Mainframe Operating Systems §Major organizations §Huge I/O capacity §Batch l Processes not requiring user interaction (payroll processing, sales reporting …) §Transaction Processing l Small requests e.g. bank system, airline systems §Time Sharing l large number of remote users Example: OS/390

Server Operating Systems §Major organizations §High end web-servers, commerce sites, file service etc. §UNIX, Windows Server, LINUX

Speechome Project, MIT l Massive petabyte (one million gigabyte) disk storage system at the Media Lab at MIT

§Multiprocessor Operating Systems §Real Time Operating Systems §Embedded Operating Systems l Simple OS: One program, one user, one machine l Examples: embedded controllers such as nintendo, cars, elevators, cellphones …

§Programmed I/O l User program makes a system call l That is translated into a procedure call for the relevant device driver l Device driver starts I/O and keeps polling the device to see if it is done (device busy status check). l When device is done it puts the data where needed. l OS returns control to user program Ways to do I/O Disadvantage?

Programmed I/O Con: §Busy waiting l Tying up CPU until I/O is done l Busy waiting is inefficient Ways to do I/O

Programmed I/O Con: Busy waiting l Tying up CPU until I/O is done l Busy waiting is inefficient Pro: §Easy to implement l Embedded systems Ways to do I/O

Interrupt Driven I/O §Driver starts the device and asks it to give it an interrupt when it is done. Ways to do I/O

Interrupt Driven I/O For example: Read from Disk Interrupt signal causes the CPU to stop what it is doing and use the interrupt number to start a interrupt service handler When the handler is done control is returned to previously running user program Information of interrupted program is saved before hand.

Direct Memory Access (DMA) Ways to do I/O

§BIOS (Basic Input Output System) is a program that resides on the motherboard. §Can read from keyboard, write to disk, write to screen etc. BIOS

§Checks how much memory is installed, keyboard etc installed or not. §Scans buses and detects devices. §Determines boot device from the list stored in CMOS memory. BIOS

§First sector from boot device is read into memory and executed. l This gives information about which partition is active. l From there a boot loader is read which loads the OS §The OS queries the BIOS to get configuration information and checks if each device has a device driver l One all device drivers founds loads them in kernel starts login program. BIOS

§First sector from boot device is read into memory and executed. l This gives information about which partition is active. l From there a boot loader is read which loads the OS §The OS queries the BIOS to get configuration information and checks if each device has a device driver l One all device drivers founds loads them in kernel starts login program. BIOS

Memory On chip cache Optical disks, EEPROM, flash RAM