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WHAT IS AN OPERATING SYSTEM? 1.2 HISTORY OF OPERATING SYSTEMS 1.3 THE OPERATING SYSTEM ZOO 1.4 COMPUTER HARDWARE REVIEW 1.5 OPERATING SYSTEM CONCEPTS 1.6 SYSTEM CALLS 1.7 OPERATING SYSTEM STRUCTURE 1.8 RESEARCH ON OPERATING SYSTEMS 1.9 OUTLINE OF THE REST OF THIS BOOK 1.10 METRIC UNITS 1.11 SUMMARY
12 OPERATING SYSTEM DESIGN 12.1 THE NATURE OF THE DESIGN PROBLEM 12.2 INTERFACE DESIGN 12.3 IMPLEMENTATION 12.4 PERFORMANCE 12.5 PROJECT MANAGEMENT 12.6 TRENDS IN OPERATING SYSTEM DESIGN 12.7 SUMMARY main( ) main( ) {{ int ; mess t msg; init( ); init( ); do something( ); while (get message(&msg)) { read( ); switch (msg.type) { do something else( ); case 1: ; write( ); case 2: ; keep going( ); case 3: ; exit(0); } }} } (a) (b) Fig. 12-1. (a) Algorithmic code. (b) Event-driven code. Interrupt handling, context switching, MMU Hide the low-level hardware Virtual memory Threads, thread scheduling, thread synchronization 1 2 3 4 5 Driver 1 Driver n File system 1 File system m 6 System call handler 7 Layer Driver 2 Fig. 12-2. One possible design for a modern layered operating sys- tem. Chap-12 Chap-11 Chap-10 External name: /usr/ast/books/mos2/Chap-12 Directory: /usr/ast/books/mos2 I-node table 1 2 3 4 5 6 7 2 38 114 Internal name: 2 Fig. 12-3. Directories are used to map external names onto internal names. found = 0; for (p = &proc table[0]; p < &proc table[PROC TABLE SIZE]; p++) { if (p->proc pid == pid) { found = 1; break; } } Fig. 12-4. Code for searching the process table for a given PID. #include "config.h" #include "config.h" init( ) #if (WORD LENGTH == 32) { typedef int Register; #if (CPU == PENTIUM) #endif / * Pentium initialization here. * / #endif #if (WORD LENGTH == 64) typedef long Register; #if (CPU == ULTRASPARC) #endif / * UltraSPARC initialization here. * / #endif Register R0, R1, R2, R3; (a) (b) } Fig. 12-5. (a) CPU-dependent conditional compilation. (b) Word- length dependent conditional compilation. #define BYTE SIZE 8 /* A byte contains 8 bits */ int bit count(int byte) {/ * Count the bits in a byte. * / int i, count = 0; for (i = 0; i < BYTE SIZE; i++) / * loop over the bits in a byte * / if ((byte >> i) & 1) count++; / * if this bit is a 1, add to count * / return(count); / * return sum * / } (a) / * Macro to add up the bits in a byte and return the sum. * / #define bit count(b) (b&1) + ((b>>1)&1) + ((b>>2)&1) + ((b>>3)&1) + \ ((b>>4)&1) + ((b>>5)&1) + ((b>>6)&1) + ((b>>7)&1) (b) / * Macro to look up the bit count in a table. * / char bits[256] = {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3, 3, }; #define bit count(b) (int) bits[b] (c) Fig. 12-6. (a) A procedure for counting bits in a byte. (b) A macro to count the bits. 3,8,13 3,8,13 3,8,13 3,8,13 26,4,9 90,2,6 4,19,20 4,6,9 4,6,9 10,30,8 5,8,1 22,2,0 10,11,5 4,2,17 88,4,3 66,4,43 7 7 77 26 34 4 5 10 0 89211 11 10 1 6 7 8 5 0 9 2 3 4 8 Bits 24 Bits 24 Bits (b) (c) (a) 22,2,0 26,4,9 5,8,1 10,30,8 4,6,9 4,19,20 90,2,6 66,4,43 88,4,3 4,2,17 10,11,5 3,8,13 Fig. 12-7. (a) Part of an uncompressed image with 24 bits per pixel. (b) The same part compressed with GIF, with 8 bits per pixel. (c) The color palette. Path I-node number /usr 6 /usr/ast 26 /usr/ast/mbox 60 /usr/ast/books 92 /usr/bal 45 /usr/bal/paper.ps 85 Fig. 12-8. Part of the i-node cache for Fig. 6-39. Title Duties Chief programmer Performs the architectural design and writes the code Copilot Helps the chief programmer and serves as a sounding board Administrator Manages the people, budget, space, equipment, reporting, etc. Editor Edits the documentation, which must be written by the chief programmer Secretaries The administrator and editor each need a secretary Program clerk Maintains the code and documentation archives Toolsmith Provides any tools the chief programmer needs Tester Tests the chief programmer’s code Language lawyer Part timer who can advise the chief programmer on the language Fig. 12-9. Mills’ proposal for populating a 10-person chief programmer team. [...]...Main program Plan Code Test modules Test system Dummy procedure 1 Dummy procedure 2 Dummy procedure 3 Deploy (a) (b) Fig 12- 10 (a) Traditional software design progresses in stages (b) Alternative design produces a working system (that does nothing) starting on day 1 . the documentation, which must be written by the chief programmer Secretaries The administrator and editor each need a secretary Program clerk Maintains the code and documentation archives Toolsmith. programmer Performs the architectural design and writes the code Copilot Helps the chief programmer and serves as a sounding board Administrator Manages the people, budget, space, equipment, reporting,. sys- tem. Chap-12 Chap-11 Chap-10 External name: /usr/ast/books/mos2/Chap-12 Directory: /usr/ast/books/mos2 I-node table 1 2 3 4 5 6 7 2 38 114 Internal name: 2 Fig. 12-3. Directories are used to map