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MINIX

MINIX. Presented by: Clinton Morse, Joseph Paetz, Theresa Sullivan, and Angela Volk. MINIX Presentation Summary. Overview MINIX Trivia Processes Input/Output Memory Management File Systems. MINIX Overview.

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MINIX

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  1. MINIX Presented by: Clinton Morse, Joseph Paetz, Theresa Sullivan, and Angela Volk

  2. MINIX Presentation Summary • Overview • MINIX Trivia • Processes • Input/Output • Memory Management • File Systems

  3. MINIX Overview • “MINIX is a free UNIX clone that is available with all the source code. Due to its small size, microkernel-based design, and ample documentation, it is well suited to people who want to run a UNIX-like system on their personal computer and learn about how such systems work inside. It is quite feasible for a person unfamiliar with operating system internals to understand nearly the entire system with a few months of use and study. “

  4. MINIX Overview (cont.) • “MINIX has been written from scratch, and therefore does not contain any AT&T code--not in the kernel, the compiler, the utilities, or the libraries. For this reason the complete source can be made available (by FTP or via the WWW).“

  5. MINIX Trivia • Written by Andrew S. Tanenbaum in 1987 • Modeled after UNIX version 7 • 12,649 lines of code, with over 3,000 comments • Written in C

  6. Processes • Overview • Processes fall into four different “layers” • Process management • I/O tasks • Server Processes • User Processes

  7. Processes (cont.) • Internal Structure of a process • Process Control Block: • No data structure specifically called the “process control block” • The process control block is an entry in the process table

  8. Processes (cont.) • Process Management • Occurs in layer 1. • All processes are stored in a tree with the init process at the root

  9. Processes (cont.) • Inter-process Communication • Is handled by the kernel • A process sends a destination and a message to the kernel, which then copies the message to destination process • A process must be waiting for the message in order to recieve

  10. Processes (cont.) • Process Scheduling • Hybrid round-robin/priority scheduler • The system sets a time quantum for every process • There are three priority settings for every process

  11. Input/Output Overview: • Interrupt Handlers • Device Drivers • Device-Independent Software • User-Level Software • Deadlock Handling

  12. User Processes Device-independent software Device drivers Interrupt handlers Hardware I/O Request I/O Reply

  13. Input/Output (cont.) • Interrupt Handlers: • Eventually handled by coding stored in mpx88.s • Saves contents in the registers of the current process • Creates a message and calls the interrupt process • After checking for the ability to send the message, the message is sent to the accepting device

  14. File System User Process Device Driver Input/Output (cont.) • Device Drivers: Processes

  15. Input/Output (cont.) • Device-Independent Software: • Uniform interfacing for the device drivers • Device naming • Device protection • Providing a device-independent block size • Buffering • Storage allocation on block devices • Error Reporting

  16. Input/Output (cont.) • User-Level Software: • Library procedures present • Ability to make system calls • Ability for conversions/formatting of text • No spooling/daemons present in the system

  17. Input/Output (cont.) • Deadlock Handling: • No dedicated I/O devices • Deadlocks occur only with implicitly shared resources • Deadlock is ignored

  18. Memory Management • Structure • Records holes • First Fit • Reasoning • Structured for a personal computer • Able to port with other systems • Memory Layout • Not located in Kernel • Message Handling • Messaging system used to communicate between memory manager and kernel

  19. File System • Responsible for mapping logical file onto physical drive • Allocates space • Manages free space • Provides file protection • Self contained C program • Can be stored on any block device (floppy, hard drive, etc.) • Can be used as a network file server

  20. File System (Cont.) • Accepts 29 different messages • How it works • Loops, waiting for a message • Uses message type to index procedure in a table • Runs procedure • Returns a value indicating failure or success

  21. File System (Cont.) • The components (always present) • Boot block • Super-block • I-node bit map • Zone bit map • I-node • Block

  22. File System (Cont.) Super block Zone bit map Block … Boot block I-node bit map I-nodes Data

  23. File System (Cont.) • Block • Manageable pieces of a file that may or may not be contiguous • Standard size is 1K • Synonymous with zone when both are the same size (standard is 1K for block and zone)

  24. File System (Cont.) • I-node • Each I-node is associated with a single file • Contains information about the file, such as owner, file size, and date modified • Stores the first 7 disk block numbers • Stores pointers to other blocks if there are more than 7 • With 1K blocks and 16-bit addresses, can store up to 64M

  25. File System (Cont.) • I-node (cont.) • Read into I-node table when a file is opened • Only one I-node in the table, no matter how many instances of the file are open • A counter in the table is used to keep track of how many instances of the file are opened • Modifications are written to disk when the counter reaches 0

  26. File System (Cont.) • Boot block • Very first thing in file system • Read into memory when the computer is first booted • Present even if the device is not bootable

  27. File System (Cont.) • Super-block • Describes the layout and structure of the file system (number of I-nodes, max. file size, etc.) • On boot or mount, read into the super-block table • Stores information not in the super-block, such as originating device

  28. File System (Cont.) • I-node / zone bit map • Read into memory on boot or mount • When a file is deleted, pointer array is used to find I-node in bit map, and bit is set to 1 • When a file is created, searches through bit map to find a free I-node • If no free I-nodes, a value of 0 is returned (I-node 0 is never used)

  29. File System (Cont.) • Directory structure • Root directory • Paths are looked up one directory at a time • Protection • Read, write, and execute bits • Owner, owner’s group, and others

  30. MINIX: Conclusion • Multi-user, multi-tasking, single threaded • Ignores deadlock • 3 levels of I/O: interrupt handling, device drivers, device-independent software • Memory managed in a sorted list of holes • 6 parts of file system: boot block, super-block, I-node bit map, zone bit map, I-nodes, blocks

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