1. Computer Organization Review and OS Introduction CS550 Operating Systems

2. Last Time What is the OS? A Resource Manager! Expected knowledge – Computer Organization – Data Structures – Basic algorithms like searching and sorting Learning about UNIX/Linux command line and text editor

3. Review of Comp. Org. A computer system consists of hardware and software It performs input, processing, and output HW consists of: CPU Main memory (RAM) Mass (secondary) storage (HDD, USB, etc.) --> provides permanence I/O (Screen, keyboard, communication) System bus (interconnect)

4. Computer Components +------------+ +------------+ | Processors | | Memory | +------------+ +------------+ ^ ^ | | --------+-----------------------+--------------------+--------------- ^ ^ ^ | | | +------------++------------++------------+ | HDD || Comm. ports|| I/O | +------------++------------++------------+

5. Interrupts Interrupts - mechanisms by which a HW component sends a signal to a CPU to stop normal execution of a program so the CPU may handle that components needs. User program +------------+ | main() | | A = 4 | | B = f(A) |-----------+ | print(B) |<------+ | +------------+ | | | | +------------+ | | | funct f(X) | | | | Y = X+1 |-------|---+ | return Y |-------+ +------------+

6. Interrupts Synchronous interrupts - calling a function and returning happens in the same way from a timing perspective. We call then return. +------------+ | main() | OS disk I/O handler | A = 4 | +------------+ | B = A+4 |---------->| Start | | C = 2*B+3 |<----------| next disk | | D = A / B | | read. | | E = D * C |---------->| | +------------+ Retrieving data from disk occurs in an asynchronous manner (order of reads and writes is unknown as is timing). One of the low level functions of the OS is to provide scheduling and interrupt handling.

7. Other OS Tools OS provides many other tools. Consists of many programs – Process management – Memory management – Device management – Security and protection – File management – Network management – Services

8. OS Structure Focus of this course is on General purpose operating systems. OS structure +--------------------------+ | GUI | +--------------------------+ | Command line interpreter | +--------------------------+ | System call interface | <-------------+ +--------------------------+ | | Process, memory, file and|. | | device management |. |<------- OS +--------------------------+. | Kernel | Hardware control | <-------------+ +--------------------------+

9. Software components of the Kernel System calls - functions and methods to interact with HW/SW (e.g. println or printf) Process manager - allows for creation, suspension (blocking), execution, termination, and destruction of running programs (processes) Process - a running program. Note that many programs run at the same time in active memory. Process manager switches programs frequently. This operation is called a context switch (also overhead).

10. Software Components of the Kernel Memory manager - controls allocation and deallocation of memory. – Has policies and mechanisms for memory management – Includes paging, segmentation (think seg. fault), and virtual memory Resource manager - manages allocation and deallocation of resources such as HW/Information entities, CPU, files, words in memory, IO, tables, etc. File manager - manages creation and deletion of files and directories – Note that files represent devices in Linux – /media/... – Note that the same file may be open in multiple places at the same time. Device manager - handles devices and provides abstraction for them.

11. Types and Categories of OSes Types – Batch – Interactive – Real-time – Hybrids Categories – General purpose – Application dependent – Single/multi-user

12. Types of Kernels Monolithic Layered Modular Micro-kernel

13. Jobs Jobs - units of work submitted to OS (a process or a group of processes is a job) – sequence of commands to OS – program in source or binary – input data used by program when needed See book and site in previous lecture for history of OSes

14. Some Current OSes UNIX MS Windows OSX Android iOS TinyOS Debian Linux – Knoppix – BCCD Ubuntu CentOS RedHat Fedora Mint OSE QNX LynxOS VxWorks Many many more