Operating System Structures Vivek Pai Princeton University COS318 Lec 2 1 Gedankenexperiment What does this program do static void Loop void static char startAddr char local printf diff is d n startAddr local startAddr local Loop int main int argc char argv Loop COS318 Lec 2 2 Mechanics Have you Subscribed to pu cs 318 Sent me mail with your details Hey it was an assignment after all Sent me a picture of yourself COS318 Lec 2 3 More Mechanics Syllabus is now complete along with goals for each lecture Preparatory readings are listed External readings are not yet included Projects are being finalized Regular lab not yet operational How do we want to handle quizzes Scheduled or random COS318 Lec 2 4 Reading Assignment Sections 1 0 1 3 inclusive Keep up with what s on home page I ll try to remember to remind you COS318 Lec 2 5 A Typical Computer from a Hardware Point of View CPU Memory CPU Chipset I O bus Network COS318 Lec 2 6 A Typical Computer System CPU CPU Memory Programs and data Operating System Software OS Apps Data Network COS318 Lec 2 7 Typical Unix OS Structure Application Libraries User space level Kernel space level Portable OS Layer Machine dependent layer COS318 Lec 2 8 Typical Unix OS Structure Application Written by programmer Compiled by programmer Uses function calls Libraries Portable OS Layer Machine dependent layer COS318 Lec 2 9 Typical Unix OS Structure Application Written by elves Provided pre compiled Defined in headers Input to linker compiler Invoked like functions May be resolved when program is loaded Libraries Portable OS Layer Machine dependent layer COS318 Lec 2 10 Typical Unix OS Structure Application Libraries Portable OS Layer Machine dependent layer COS318 Lec 2 Guts of system calls All high level code 11 Typical Unix OS Structure Application Libraries Portable OS Layer Machine dependent layer COS318 Lec 2 Bootstrap System initialization Interrupt and exception I O device driver Memory management Kernel user mode switching Processor management 12 Another Look Unix Onion Applications User and Kernel boundary OS Service Device Hardware Driver COS318 Lec 2 13 What s An Application Four parts segments Code Text instructions Data initialized global variables Stack Heap What s a stack and heap COS318 Lec 2 14 OS Service Examples Examples that are not provided at user level System calls file open close read and write Control the CPU so that users won t stuck by running while 1 Protection Keep user programs from crashing OS Keep user programs from crashing each other Examples that can be provided at user level Read time of the day Protected user level stuff COS318 Lec 2 15 Processor Management Goals Overlap between I O and computation Time sharing Multiple CPU allocations CPU I O CPU CPU CPU I O Issues CPU Do not waste CPU I O resources Synchronization and mutual CPU CPU exclusion CPU Fairness and deadlock free COS318 Lec 2 16 Memory Management Goals Support programs to run Allocation and management Transfers from and to secondary storage Issues Efficiency convenience Fairness Protection COS318 Lec 2 Register L2 10x Memory 200x Disk 10Mx Tape 100Mx 17 x86 Architecture Registers 31 15 87 0 AL BL CL DL AH BH CH DH BP SI DI SP 16 bit 32 bit AX BX CX DX EAX EBX ECX EDX EBP ESI EDI ESP 15 0 CS DS SS ES FS GS Segment registers General purpose registers EFLAGS register EIP Instruction Pointer register COS318 Lec 2 18 x86 Memory 232 1 31 24 23 16 15 87 0 Byte 7 Byte 6 Byte 5 Byte 4 Byte 3 Byte 2 Byte 1 Byte 0 0 Byte order is little endian COS318 Lec 2 19 I O Device Management Goals Interactions between devices and applications Ability to plug in new devices Issues Efficiency Fairness Protection and sharing User 1 User n Library support Driver Driver I O device I O device COS318 Lec 2 20 Window Systems All in the kernel Windows Pros efficient Cons difficult to develop new services All at user level Pros easy to develop new apps Cons protection Split between user and kernel Unix Kernel display driver and mouse driver User the rest COS318 Lec 2 21 File System A typical file system Open a file with authentication Read write data in files Close a file Can the services be moved to user level User 1 User n File system services File COS318 Lec 2 File 22 Bootstrapping Power up a computer Processor reset Set to known state Jump to ROM code Load in the boot loader from stable storage Jump to the boot loader Load the rest of the operating system Initialize and run Boot loader COS318 Lec 2 Boot loader OS sector 1 OS sector 2 OS sector n 23 System Boot Maps to FFFFFFF0h 232 16 Power on processor waits until Power Good Signal Processor jumps on a PC Intel Inside to address FFFF0h 1M 1 048 576 220 FFFFFh 1 FFFFFh FFFF0h 16 is the end of the first 1MB of system memory The original PC using Intel 8088 had 20 address lines FFFFFFF0h is a JMP instruction to the ROM BIOS startup program COS318 Lec 2 24 ROM BIOS startup program 1 POST Power On Self Test If pass then AX 0 DH 5 586 Pentium Stop booting if fatal errors and report Look for video card and execute built in ROM BIOS code normally at C000h Look for other devices ROM BIOS code IDE ATA disk ROM BIOS at C8000h 819 200d Display startup screen BIOS information SCSI disks must often provide their own BIOS Execute more tests memory system inventory COS318 Lec 2 25 ROM BIOS startup program 2 Look for logical devices Label them Serial ports COM 1 2 3 4 Parallel ports LPT 1 2 3 Assign each an I O address and IRQ Detect and configure PnP devices Display configuration information on screen COS318 Lec 2 26 ROM BIOS startup program 3 Search for a drive to BOOT from Floppy or Hard disk Boot at cylinder 0 head 0 sector 1 Load code in boot sector Execute boot loader Boot loader loads program to be booted If no OS Non system disk or disk error Replace and press any key when ready Transfer control to loaded program Is it okay to boot at first sector on the floppy or disk COS318 Lec 2 27 Ways to Develop An Operating System A hardware simulator A virtual machine A good kernel debugger When OS crashes always goes to the debugger Debugging over the network COS318 Lec 2 28