1. CGS 3763 Operating Systems Concepts Spring 2013
Dan C. Marinescu
Office: HEC 304
Office hours: M-Wd 11: :30 AM

2. Lecture 5 – Wednesday, January 16, 2013
Last time:
Operating Systems:
State and events; Event-driven-software
Discussion of problems from the textbook
Today:
The kernel of an OS
Protection – user and kernel mode execution
OS services
Next time
System calls
Kernel data structures
Reading assignments:
Chapter 2 of the text book
The computer architecture material
12/7/2018

3. The main functions of a computer
Transform in formation  the interpreter
Store information  memory hierarchy
Communicate  communication links
12/7/2018

4. The basic operation of an interpreter
12/7/2018

5. Privileged and non-privileged instructions
To manage the resources of a system the kernel has to operate with a higher level of privileges.
Two modes of operation
Kernel mode
User mode
Two types of instructions:
Privileged instructions  can only be executed in kernel mode
Non-privileged instructions  can be executed in kernel and in user mode
System calls
Allow a user to communicate with the kernel and request operations that can only be carried out by the kernel.
12/7/2018

6. Tight coupling between interpreter and storage
We need a memory enforcement mechanism; to prevent a thread running the code of one module from overwriting the data of another module.
Address space  the range of memory addresses a thread is allowed to access.
Close relationship between a thread and an address space.
Lecture 15

7. Virtualization of storage - Virtual memory
Address space  the storage a thread is allowed to access.
Virtual address space – an address space of a standard size regardless of the amount of physical memory.
The physical memory may be too small to fit an application; otherwise each application would need to manage its own memory.
The size of the address space is a function of the number of bits in an address. For example, 32 bits addresses allow an address space of (4 Gbytes), 64 bit addresses allow 264
Virtual Memory - a scheme to allow each thread to access only its own virtual address space (collection of virtual addresses).
Lecture 15

8. Memory map of a process
Lecture 15

9. Questions What do we mean by a memory hierarchy?
Why do we need a hierarchy of memory?
What is virtualization?
What is virtual memory?
What is an interrupt?
What types of interrupts can you identify?
12/7/2018

10. Kernel functions Program execution: Interrupt handling:
Error handling:
Job sequencing:
Input/Output operations:
File system manipulation:
Scheduling:
Resource Allocation:
Accounting of computer resources:
Protection:
12/7/2018