[Operating System] Introduction and System Structures

Introduction and System Structures

Operating System

Definition (Wiki, 2012)

• An operating system is an interface between hardware and user
• An OS is responsible for the mgmt and coordination of activities and the sharing of the resources of the computer
• The OS acts as a host forcomputing applications run on the machine
  • As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications
• Almost all computers (including handheld computers, desktops, supercomputers, video game consoles) as well as some robots, domestic appliances (dishwashers, washing machines), and portable media players use an operating system of some type

Definition (Wiki, Now)

• An OS is a system software that manages computer hardware, software resources, and provides common services for computer programs
• The operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it
• Operating systems are found on many devices that contain a computer, from cellular phones and video game consoles to web servers and supercomputers

Market share (~ Now ~)

• General-purpose personal systems OS
  • MS Windows 75+%
  • MacOS 15+%
  • Linux ~2%
• Mobile OS
  • Google Android 70~90%
  • Apple iOS 10+%
  • Others ~1%
• Server and supercomputing systems OS
  • Linux distributions are dominant

OS functions

• User interface (for user convenience)
  • System call interface
• Resource management(for efficiency)
• Process management
• • Networking / Security & Protection

User interface (for user convenience)

• CLI(Command Line Interface)
  • CUI(Character(Text)User Interface)
• GUI(Graphical User Interface)
• EUCI(End-User Comfortable Interface)
  • HCI(Human-Computer Interaction)
  • UX(User eXperience)

Resource management (for efficiency)

• Processor management
• Memory management
• File management
• I/O management

Process management

• Process management

• Thread management

• Networking/Security+Protection

Compute System Organization

OS classification

OS Classification Criteria

• Number of concurrent users
  • Single-user system
  • Multi-user system
• Number of concurrent processes
  • Single-tasking system
  • Multi-tasking system (Multiprogramming system)

• Job processing mechanism (Computing paradigm)
  • Batch systems
  • Interactive systems (Time-sharing systems)
  • Personal computing
  • Parallel/Distributed computing
  • Real-time system
  • Mobile computing
  • Cloud computing
  • Ubiquitous computing

Single-user system vs. Multi-user system

• Single-user system
  • Only one user can use the system at a time
  • The user owns all the system resources
    • Simple protection mechanism
  • Mainly used for micro-computers or personal computers
  • MS-DOS, MS Windows 95/98/…/10
• Multi-user system
  • Several users can use the system simultaneously
  • Protection mechanisms are necessary to control access to system resources (including files)
  • Requires multi-tasking
  • Requires more complex OS functions/facilities
  • Unix, Linux

Single-tasking system vs. Multi-tasking system

• Single-tasking system
  • Only one process can exist in the system at a time
    • A process can start execution only after current process leaves the system
  • Single-user system
  • Simple OS structure
  • Mainly used for micro-computers or personal computers
  • MS-DOS
• Multi-tasking system
  • Multiple processes can exist in the system simultaneously
  • Requires concurrency control and synchronization mechanisms
  • Complex OS structure
  • Unix, Linux

Computing Paradigm

OS Structure

OS Structure

• Kernel
  • Nucleus part of OS (memory resident after booting)
  • Supports the functions that are frequently used for applications
  • Mainly supports resource management functions
  • Also called
    • Nucleus, supervisor program, resident program, control program
• Utilities
  • Non-resident program, service program
  • Mainly supports service functions (including UI functions)

Booting

• Bootstrap program (bootstrap loader)
  • Locate and load the OS kernel into memory
    • Initial program to be executed when a computer to start running
  • Initializes all aspects of the system
    • CPU registers
    • Device controllers
    • Memory contents
  • Stored in ROM in a form of firmware
  • May use two-step process in which a simple bootstrap loader fetches a more complex boot program from disk, which in turn loads the kernel

Functions of OS

Process Management

• Process
  • Program in execution
  • Entity that services user’s request and/or runs user program
• Process management functions
  • Creation/deletion
  • Dispatch(schedule)/preemption/block
  • Suspension/resumption
  • Process synchronization, Inter-process communication
  • Deadlock handling
• Data structure for process management
  • PCB (Process Control Block)

Processor Management

• Process scheduling
  • Determines order of process execution for a processor
• Processor assignment
  • Placement of processes to each processor in the system

Memory management

• Multi-user, multi-tasking system
  • Memory allocation/deallocation
  • Free space management
  • Memory protection
• Memory allocation schemes
  • Total contiguous allocation
  • Virtual memory system

File management

• File
  • Logical storage unit
• Management of user and system files
• Supports hierarchical directory structure
• File/space management functions
  • Creation/deletion of files/directories
  • Support of primitives for file/directory manipulation
  • Mapping of files onto secondary storage
  • Storage space allocation
  • Free space management
  • File backup service (X)

I/O Management

• Buffer pool
  • Data transmission between applications and I/O devices
  • In the kernel space of memory

Secondary storage managerment

• Disk management
  • Disk scheduling
• Related to file system management

Other management functions

• Networking
• Security and protection system
• Etc

Dual Mode Operations

Two separate modes

• Mode bit in the CPU indicates the current mode
  • User mode
    • Executing on behalf of user application
  • Kernel mode (supervisor mode, privileged mode)
    • Executing on behalf of operating system
• Mode change
  • When a trap or interrupt occurs, the H/W switches from user mode to kernel mode

Interrupt and trap

• Interrupt
  • Unexpected external event
  • From either the H/W or the S/W
    • H/W may trigger an interrupt by sending a signal to the CPU
• Trap
  • Software-generated interrupt caused by
    • An error of the running program
      • Exception
    • A specific request from a user program
      • System call

Privileged instruction

• Machine instructions that can be executed only in kernel mode
• Examples
  • I/O control
  • Timer management
  • interrupt management
  • Switching to user mode
  • Etc

---

• Manipulate memory management register
  • LGDT, LLDT, LTR, LIDT, SGDT, SLDT, SIDT, STR
• Load and store control registers
  • MOV {CR0~CR4}
• Invalidate cache and TLB
  • INVD, WBINVD, INVLPG
• Performance monitoring
  • RDPMC, RDTSC, RDTSCP
• Fast System Call
  • SYSENTER, SYSEXIT

System Call Interface

System calls

• Interface between applications/processes and the OS
• Services that OS provides to applications/processes
  • Means for a user program to ask the OS to perform tasks reserved for OS on the user program’s behalf
  • Means used by a process to request action by the OS
• Executed by a generic trap instruction
  • syscall instruction in MIPS R2000

• Process control
  • Create, terminate, load, wait, etc.
• File management
  • Create, delete, open, close, read, write, reposition, etc.
• Device management
  • Request, release, read, write, etc.
• Information management
  • Get/set time/date, get process/file/device attributes, etc.
• Communications
  • Create/delete connection, send/receive messages, etc.
• Etc

in Unix

Interrupts and Traps

System Calls, Interrupts, and Exceptions

Virtualization

Hardware virtualization

• Hardware virtualization or platform virtualization refers to the creation of a virtual machine that acts like a real computer with an operating system. Software executed on these virtual machines is separated from the underlying hardware resources
• In hardware virtualization, the host machine is the machine that is used by the virtualization, and the guest machine is the virtual machine
• Abstraction of the HW of a single computer into several different execution environments, thereby creating the illusion that each separate execution environment is running its own private computer
  • Each process is provided with a virtual copy of the underlying computer
  • Share the same H/W, yet run several different execution environments (different OSs) concurrently

OS virtualization

• OS virtualization is a server virtualization method where the kernel allows for multiple isolated user-space instances
  • Such instances, sometimes called containers, virtual private servers (VPS), or jails, may look and feel like a real server from the point of view of its owners and users
• OS virtualization usually imposes little to no overhead, because programs in virtual partitions use the OS’s normal system call interface and do not need to be subjected to emulation or be run in an intermediate virtual machine

Concept (Hardware virtualization)

Types of Virtualization

• Para-virtualization
  • Modified guest OS
• Full-virtualization
  • Unmodified (native) guest OS
• Hybrid virtualization
  • Modification for some components of guest OS and no modification for others

Types of VMM (Hypervisor)

• Type-1 (baremetal)
  • VMM runs directly on hardware
• Type-2 (hosted)
  • VMM runs on a host OS
• Type-3 (hybrid)

Benefits

• Server consolidation
  • Underutilized servers to VMs
  • Significant cost savings (equipment, space, power)
  • Can be used for virtual desktops
• Simplified management
  • Datacenter provisioning and monitoring
  • Dynamic load balancing
• Improved availability/reliability
  • Automatic restart, fault tolerance, disaster recovery
• SW development
  • Testing

• Example
  • VMware
  • Xen (Citrix → Linux Foundation)
  • KVM (Red Hat)
  • Virtual box (Oracle)
  • Etc

Cloud Computing

Cloud computing

• Type of computing that delivers computing, storage, and even applications as a service across a network
• Logical extension of a virtualization

Types of cloud computing

• SaaS
  • One or more applications available via the Internet
• PaaS
  • A SW stack ready for application use via the Internet
• IaaS
  • Servers or storages available over the Internet

Summary

• OS functions
  • Resource management, process management
  • User interface
• OS classification
  • Open system, Proprietary system
  • Criteria
    • # of concurrent users, # of concurrent processes
    • Job processing mechanisms (Computing paradigm)
• OS structure and functions
  • Kernel, Utilities
• Dual mode operations, system calls, and interrupts
• Virtualization