03/25 Lecture 01

Know the hardware, the following is a list of hardware that we are going to discuss this quarter (in this class)

Hardware List:

• CPU
  • We are mostly only going to care about single core CPU in this course
  • recall registers:
    • %rip: address of the next instruction
      • OS is responsible for setting up %rip for start of process
    • %rsp: store the stack pointer of the current process(top of the stack)
• DRAM (physical memory)
  • slower compare to CPU (that’s why we use the cache -recall 351)
  • data and instructions must be first loaded to DRAM before it runs
    • Why? so they can have physical address
  • DRAM is volatile
    • it lose data between power cycles
  • Memory is byte addressable
    • means we can read and write any byte directly
• Disk
  • there are HDD and SSD
    • even though SSDs are way faster than HDDs, they are still a lot slower than memory
  • cheap
  • persistent
    • means they preserve data between power cycles
  • block addressable
    • Data can only be read and written with page sized chunks
• IO Devices (not important)
  • input
    • mouse
    • keyboard
  • output
    • monitor
    • headphones
    • speakers
  • Network Adapter (NIC)

OS Roles

What is Operating System?

Things to know:

• a program abstract and manage hardware for user programs
• We want the OS to have: (from textbook, where it has more details)
  • Reliability
  • Security
  • Privacy
  • Fair Resource Allocation

OS need to provide abstractions for user processes

• OS Abstractions:
  • CPU ⇒ processes
  • DRAM ⇒ Virtual Memory
  • Storage ⇒ Files, Directories
  • Network ⇒ TCP, UPD, …
• Why do we need to provide these abstractions?
  • Ease of use for the user process
  • provide simplified services to user
    • storage ⇒ files: creates names files, folders to organize, user do not need to deal with pages
    • DRAM ⇒ virtual memory: a process owns the entire address space (351 covered this)
  • mask hardware limits
    • file system: hides block sized by bytes
      • file only handles bytes
    • virtual memory: allows process to user more than physically available
  • Common Interface
    • allows process to share files with each other
    • portable interface (a good example would be the POSIX file system)
  • managed access
    • resource management
      • schedule processes onto a single CPU
      • sharing of physical memory (v table)
    • isolation
      • process can’t read each other’s memory
      • process can’t read OS’ memory
    • managed (controlled) sharing

03/27 Lecture 02

OS prevent process from doing certain things

How?

• Option 1 (almost always wrong):
  • OS can look through process’ binary file and detect bad instruction
  • Why not?
    • process might dynamically change its code