Stýrikerfi Cheat Sheet

Instru­ction cycle is fetch, decode, execute
Cache er small, very fast memory on processor for recently used memory content for quick access
Memory Hierarchy. Fast, small, expensive on top, slow, large, cheap on bottom

Objectives of OS: Conven­iance, effici­ency, evolution
Multip­rog­ram­ming: Processes use the same Processor
Batch proces­sing: One program executed before the next one is started
Processes: A program in execution
Resource manage­ment: Fairness, Differ­ential respon­siv­eness, effiency

Instru­ction trace : Sequence of instru­ctions executed for a process
Process states : ready, running, block, suspend.
Process control block: Contains inform­ation for OS to control processes
PCB Stack = Identi­fic­ation, State, priority, pc, memory pointers, context data, io status, accounting inform­ation.
Kernel mode has access to all, user should be restricted to protect the os.

Process can have one or more threads. Threads are execution units within processes while processes are binaries. Process has one process control block while threads gets it's own space on the stack and control block. Threads share the state and resources of that process

Single buffer - process writes to buffer than has to wait for I/O to write and reverse. Double buffer - Process can write to one buffer and read another, don't have to wait. Circular buffer uses more than 2 buffers.
Blocking i/o - process continues in non blocking, os takes over if it is blocking

Race condition : "­los­er" makes the last change, affects all.
Mutual exclusion: only one process can access code or data.
Produc­er/­Con­sumer
Producer puts data in buffer, consumer takes data from buffer.
If there is no data consumer sleeps and producer wakes him when he adds data.
If buffer is full, producer sleeps and consumer wakes him when he takes data.
Reader­/Writer problem
The conditions that must be satisfied are as follows
1.Any number of readers may simult­ane­ously read the file
2.Only one writer at a time may write to the file, no reader may read it
Monitors must be invoked with a call to a monitor procedure. uses wait and signal, if no process is waiting the signal is lost.
Message passing: direct and indirect.

Transl­ation lookaside buffer: checks the TLB table and if it's a hit it gets the frame number immedi­ately and can add the offset and find the data it needs else it has to look up the address in the page table.

Page replac­ement: FIFO, LRU, Optimal, Clock.