Run-time environment

virtual machine/ 확장 머신 : 하드웨어 이름만 알고 있으면 불러서 쓸 수 있다.
멀티프로그래밍: 일정 시간: 여러개 일이 잘라서 처리 - > resource 관리해줘야 함

Machine-dependent os features

OS 특징 ( 전체적으로 resource 관리)

interrupt processing
process scheduling
i/o supervision
management of real memory
mag of virtual memory

Interrupt processing

흐름이 변화한다. 프로그램 실행하다가 중간에 interrupt 발생 → interrupt 먼저 처리해줘야 한다.
언제 발생: 아무도 모름. ( 프로그램과 인터럽 서로 관계 없다 )
- 입출력 처리 땜에 발생할 수 있다 ( 왜냐: 속도…)
- 0으로 나워서
- 각 프로세스 시간 있다.
interrupt occur → interrupt processing routine 실행

SIC/XE interrupt type

I - SVC

II- Program

III- Timer

IV- I/O

interrupt 발생 - > CPU 상태 저장해야함( interrupt work area 공간에서 )
timer interrupt 발생 → 또 timer interrupt 발생 - > 안됨.

Context switching

= saving and restoring cpu status n register

Mask

Is used to control whether interrupts are allowed

→ prevent certain intterrupts form occuring which the 1st one is being processed

to be masked

to be pending

Nested interrupt processing

I/O interrupt → status of A is saved → timer interrupt → control is transfered to timer interrupt handler → LPS instruction → return to I/O interrupt handler.

Process scheduling

management of the CPU by switching control among various competing processes

time-slice: max amount of CPU time the task is allowed to use
- running state→ ready state
dispatching = selection of a process and give it control
PSB: process status block
ETB: event status block
preemptive process scheduling: transfer control to the highest priority process

Algorithm for wait& signal

examines ESBFLAG → not occured → ESBQUEUE

I/O supervision

I/O channel: hardware to take care of transfering data and controlling I/O devices

Management of real memory

fixed partition

Using when sizes of job tend to cluster around certiain common value & job size does not change frequently
fixed size and position

variable partition

Is allocated dynamically
The OS needs to maintain a linkedlist of free memory area
first-fit allocation(first free area) or best-fit allocation(smallest area)
PMT( page map table) : mapping pages onto page frames

Management of virtual memory

virtual memory may be larger than total amount of real memory
backing store and virtual-to-real mapping are invisible to user

Virtual-to-Real mapping using a page map table

implement of the page table as array in central memory can be inefficient
using technique in conbination with high speed buffer
demand-paging sys: avoid wasted memory
threshing: collapse of service cuz high page rate
avoid by page fault rate to be much lower ( memory references)
page fault error: a page has not been loaded to real memory→ program interrupt called page fault