Lecture 2 Information Representation and Program Execution

Lecture Plan Overview

• The lecture covers information representation, program translation and execution, memory management, and the OS role.

Understanding Systems for Programming

• All computers share basic hardware/software components; CPU, RAM, storage, OS, programs, utilities and applications.
• These hardware/software components are interdependent.
• Computer scientists focus on the software aspect.
• Software development requires understanding all system components.

Key Aspects to Understand

• How to manipulate information using bits and context which forms information.
• Programs are translated to reconcile program and hardware requirements.
• Programs may use very large numbers, but hardware might use 32-bit operations.
• Single program instructions can translate into many machine instructions, with code often drawn from libraries.
• Program execution depends on hardware architecture and organization.
• Programs are affected by the OS and memory architecture, including caching.

Information as Bits and Context

• Data alone is meaningless without interpretation or context.
• Data of equal meaning can exist in ASCII, Hex or Binary representations

Data vs. Information

• "Data" is raw, uninterpreted bits, while "information" is data with meaning derived from context and interpretation

Data Representation

• The same data can be represented and interpreted as 8-bit integers, 32-bit integers, and text.

Context Significance

• The meaning of data is derived from its context, as seen in "hello.c" as text, 8-bit integers, or 32-bit integers.
• Interpretation depends on the file type, memory section or CPU.
• Manipulation of a sytem, depends on knowing how data is represented and interpreted.

Program Translation

• Program translation is a fundamental systems process.
• Programs are typically translated multiple times to allow running on a system.
• Java programs are translated to byte code then machine code.
• C programs are translated into assembly code, then object code, and finally into executable code.
• The program is transformed at each translation stage.
• Each stage relies on the previous one and the translator.
• All stages affect the final version of the program

C Compilation Chain

• The C compilation chain involves preprocessing, compiling, assembling, and linking to create an executable

Assembly File

• Assembly files contain instructions that directly control the processor and system

Reasons to Understand Compilation

• Ability to optimize program performance by writing efficient code.
• Enables better code choices that result in better performance
• Helps avoid security holes by knowing how programs are compiled.
• Facilitates understanding and resolution of linking errors stemming from multiple definitions or incorrect order.

Program Execution Factors

• Program execution intrinsically depends on hardware, including CPU, instruction set, word size and implementation.
• RAM characteristics, such as amount, speed, and caching, also play a key role.
• The bus' word-size, speed, and coherency protocols are also important.

Hardware Components

• Crucial components include the CPU, RAM, and a bus for inter-device communication.

Fetch-Decode-Execute Cycle

• The CPU operates in an infinite loop: fetching instructions from memory, decoding and then executing them.
• Execution may involve reading/writing to memory, modifying CPU registers, and altering program flow.

Performance Variation in Instructions

• Instructions involving memory access are slower due to data transfers.
• Speed can be increased by minimizing memory accesses and utilizing cache-friendly practices.

Cache Use

• Caches are smaller, faster memory that sit between the CPU and main memory.
• Caches store commonly accessed data, reducing main memory access.
• Caches are closer to CPU components but cost more.

Memory Hierarchy

• Faster storage is inserted between processor and slower, larger storage.
• Each level of storage works as a cache for the level below.
• Main memory (DRAM) is slower and cheaper compared to SRAM caches (L1, L2, L3 caches).
• Understanding where data is stored, used, and cached is key for proficient programming.

OS Role

• OS manages hardware like CPU, I/O, and RAM.
• OS provides an execution environment for programs.
• The OS acts as an intermediary and protects hardware/software/users.
• The OS provides abstractions that facilitate computer resource access.

Resources and Abstractions

• The OS abstracts CPU as processes, RAM as memory address space, and secondary/network/peripheral devices as files.

Key Abstractions

• Process represents a running program with associated memory space and file access.
• Memory (address) Space defines the accessible memory range, where each location is uniquely identified and accessed.
• File abstraction models data streams addressable via a name or descriptor in the O/S's system.

Process fundamentals

• Processes are operating system abstractions of a running program that can be run concurrently.
• Traditional systems are sequential, but support more processes than processors through interleaving.
• Context switching manages Instructions interleaved between processes.

Virtual Memory

• Virtual Memory abstracts memory, providing each process the illusion of exclusive use.
• The virtual address space includes memory invisible to user code.

Files as Abstraction

• Files are sequences of bytes used to model devices and networks.
• Files offer a uniform view of I/O devices to applications.

Process Composition

• Composed of CPU context (registers, program counter), memory space(stack, heap, data, code), and at least one thread of execution.

Thread of Execution

• An active execution of program code.
• Its location is stored in the program counter (PC).
• The thread depends on CPU context and memory content.

Key Take-Away Points

• Information is data plus context for interpretation.
• Programs Translation, affects execution, and depends on the operating system and hardware.
• Systems are architected to mitigate the cost of memory access.
• Operating System provides the mechanisms, abstractions, and environment for execution.

Explore information representation using bits and context. Understand how programs are translated to bridge the gap between program requirements and hardware capabilities. Learn about the crucial role of the operating system and memory architecture in program execution.