Lecture 2 Computer Systems: Components and Execution

Lecture Plan Overview

• This lecture introduces key concepts for understanding how systems work
• Core topics include information representation, program execution, and the operating system's role

Basic Computer Components

• All computers share the same basic hardware: CPU, RAM, and storage
• Software includes operating systems, programs, system utilities and user applications
• System components are interdependent; a missing or malfunctioning component can render the computer useless
• Computer scientists primarily focus on software development

Key Areas of Understanding for Programming

• How to manipulate information using bits and context
• How programs are translated to reconcile program and hardware requirements
• How programs are executed
• How programs are affected by their environment, especially via the OS and memory architecture

Bits and Context

• Data alone has no inherent meaning
• Data derives meaning from its interpretation or context
• The same data can be represented in ASCII, Hex, Binary etc
• The code printf(“Hello, World!\n”); will be interpreted differently based on context

Data vs. Information

• Data can represent as a series of bytes (e.g., 23 69 6e 63... ), which is meaningless on its own
• Information is interpretable data that has meaning (e.g., #include <stdio.h> int main()...)

Same Data, Different Interpretations

• A series of bytes can have different meanings based on the interpretation.
• It can be interpreted as ASCII text, 8-bit integers, or 32-bit integers.

Context Matters

• Context is essential for making data meaningful
• Hello.c can contain text, 8-bit integers, or 32-bit integers depending on the interpretation
• Everything in a system is up to interpretation and understanding requires knowledge of data representation

Program Translation Details

• Program translation is a fundamental system process
• Programs are translated multiple times to allow execution
• Java programs translate to byte code and then machine code, while C programs translate to assembly and then executable code
• Programs are transformed at each stage of translation
• Each translation stage depends on the previous stage and the translator

C Compilation Chain

• The compilation chain involves a preprocessor, compiler, assembler, and linker
• Source code is processed and compiles into assembly, which is assembled and linked to libraries to create an executable

Assembly Files

• Assembly files are a human-readable form of machine code that use textual representations of instructions

Reasons to Care About Program Translation

• Optimizing performance involves writing efficient code and choosing appropriate code structures
• Understanding compilation helps avoid security vulnerabilities like stack and buffer overflows
• Knowledge of linking helps resolve errors related to multiple definitions and header files

Program Execution Factors

• Program execution depends on system hardware
• Important hardware features include the CPU (processor), its instruction set, word size, and implementation
• RAM (memory) considerations include available amount, speed, and caching
• Bus (interconnect between devices) features include data transmission size, speed and coherency protocols

CPU Operation

• The CPU performs operations based on the instructions, using Fetch-Decode-Execute loop
• Execution involves reading/ writing to memory, modifying CPU state, and jumping to other program locations

Speeding Up Program Computation

• Instructions involving memory are slower
• Memory accesses slows the CPU, since memory accesses require data transfers across the bus
• You can speed up computation by reducing memory accesses and caching

Caching

• A cache is a smaller, faster memory
• Caches store commonly accessed data and reduce the number of accesses to slower main memory
• Proximity to the CPU enables reduced access times

The Memory Hierarchy

• Fastest storage: CPU registers
• L1 cache: holds cache lines retrieved from the L2 cache
• L2 cache: holds cache lines retrieved from the L3 cache
• Main memory: holds disk block retrieved from local disks
• Local secondary storage: holds files retrieved from disks on remote network servers
• Remote secondary storage: distributed file systems, Web servers

Role of the Operating System

• Managing computer hardware like CPU, I/O devices, and RAM
• Provides an execution environment
• Acts as intermediary between computer, user, and programs
• It provides abstractions for accessing computer resources

Resources and Abstractions

• Some relationships between hardware resources and OS abstractions:
• CPU is abstracted as processes
• RAM becomes memory address space
• Secondary storage(HD), network, and peripheral devices are presented as files

Key Operating System Abstractions

• Processes represent running programs
• They are associated with a memory space and can access files
• Memory space includes a range of memory locations, each with a unique address
• Files are streams of data identified by a name or descriptor

Processes in the OS

• Processes is an OS abstraction of a running program with concurrent execution capabilities
• Instructions can be interleaved with processes
• Context switching makes this possible

Virtual Memory

• Virtual memory is an abstraction providing each process with the illusion of exclusive memory
• The virtual address space has specific areas, with some being invisible to user code(Kernel Virtual Memory)

Files As Abstractions

• Files are sequences of bytes that can model keyboards, displays, and networks

Process Composition in Detail

• Process is created of multiple elements, for example the CPU Context, the memory Space, and at least 1 Thread
• CPU Context deals with general and special Registers, with the Program counter
• Memory Space manages stack(local variables), heap(dynamic memory), data(global variables) and the program code

Details of Threads

• A thread is an active execution of program code with its location stores in PC (program counter)

Key Takeaways

• Information is fundamentally bits with context
• Programs needs translation before execution and is reliant on the OS
• Memory and storage access dominates execution cost and needs architectural mitigation
• The OS manages system via abstractions while providing the environment for execution

Introduction to computer systems architecture, including hardware components like CPU, RAM, and storage. Focuses on how software interacts with hardware, the role of the operating system, and the importance of understanding information manipulation for effective programming.