Udacity/ud923/Intro to Operating System

L15 / IO Management

* OS support for I/O devices
    - Basic devices features
        - control registers: command, data transfers, and status
        - micro-controller: cpu
        - on device memory
        - other logic: A/D converters
    - devices are connected through peripheral component interconnect(PCI)
    - access device register is equal to memory load/store
    - There are two paths a device can use to reach CPU
        - Interrupt
            - pros: can be generated as soon as possible
            - cons: interrupt handling steps
        - Polling
            - pros: it's convenient for OS
            - cons: delay or CPU overhead
        - Typical device access: a user process -> kernel -> driver -> device
    - virtual file system can solve the following three challenges
        - files are on more than one device
        - devices work better with other file systems implementations
        - files are not on a local device
    - virtual file system abstractions on linux
        - file: an element on which the VFS operate
        - file descriptor: OS representation of a file
        - inode: persistent representation of a file, "index"
        - dentry: directory entry
        - superblock: file system specific information regarding the layout

wowmomsos 发表于 2019-2-6 01:08
同学我看了一下，xuetangx上的os课有好几门，您说的是哪门呢？

就是“操作系统（自主模式）”，是清华的老师教的，要学的话可以一块儿交流呀，我过了年还想吧里面的lab好好做一做

L16 / System Virtualization

• benefits of virtualization
  
  • consolidation: decrease cost, improve manageability
    
    
  • migration: availability, reliability
    
    
  • security
    
    
  • debugging
    
    
  • support for legacy OS
    
    
    
  
  
• two main models of VM
  
  • Bare-metal/Hypervisor-based(type 1): virtual machine monitor(VMM), which is called hypervisor, manages all hardware resources and supports execution of VM
    
    
  • Hosted(type 2): host OS owns all the hardware
    
    
    
  
  
• virtualization requirements
  
  • present virtual platform interfaces to VMs
    
    
  • provide isolation across VMs
    
    
  • protect guest os from apps
    
    
  • protect VMM from guest OS
    
    
    
  
  
• main technical approaches in popular virtualization solutions
  
  • hardware protection levels, such as x86 has 4 levels
    
    
  • processor virtualization
    
    
  • binary translation
    
    
  • paravirtualization
    
    
  • memory virtualization
    
    
  • device virtualization
    
    
    
  
  
  

ilove6169 发表于 2019-2-6 18:25
就是“操作系统（自主模式）”，是清华的老师教的，要学的话可以一块儿交流呀，我过了年还想吧里面的lab ...

我看了下，好像只有清华校内能访问联系资料。
可惜不是我能访问到的。

L20 / Datacenter Technologies

• multi-tier architectures for internet services
  
  • homogeneous architecture: each node can do any processing step, so that it keeps the front-end simple
    
    
  • heterogeneous architecture: different nodes/tasks/requests/data don't uniformly be accessed
    
    
    
  
  
• cloud computing benefits
  
  • capacity scales elastically with demand
    
    
  • scaling in instantaneous, both up and down
    
    
  • cost is proportional to demand to revenue opportunity
    
    
    
  
  
• separation of responsibilities
  
  • infrastructure as a service: Amazon EC2
    
    
  • platform as a service: Google App Engine
    
    
  • software as a service: gmail