ISA and Executable Files Quiz

Executable Files

• An executable file, also known as a binary, is a program that can be understood and run by a processor.
• The processor takes the sequence of 0s and 1s in the executable file and generates an output based on the instructions.

Computer Understanding

• Computers are not capable of understanding complex instructions like complex mathematical calculations or natural language questions.
• They only understand simple instructions, like adding or multiplying two numbers.
• The set of instructions a processor understands is called its instruction set architecture (ISA).

ISA Design

• An ISA defines the structure of instructions, how they are used, and their interactions with peripheral devices.
• ISAs aim to be complete, concise, generic, and simple.
• Completeness is crucial for covering all necessary operations, while genericity, conciseness, and simplicity are subjective and depend on specific design choices.
• Key questions in ISA design include the number of instructions, their functionalities, and their complexity.

RISC and CISC Architectures

• There are two main types of ISA architectures: Reduced Instruction Set Computing (RISC) and Complex Instruction Set Computing (CISC).
• RISC focuses on having a small set of simple instructions that can be executed efficiently. ARM processors used in smartphones and tablets are examples of RISC processors.
• CISC uses a large set of complex instructions, often with varying numbers of arguments. Intel x86 processors common in desktops and laptops use CISC.

Church-Turing Thesis

• The Church-Turing thesis states that any real-world computation can be translated to an equivalent computation on a Turing machine.
• This thesis is not a theorem, but a hypothesis that has not been disproven.
• A Turing machine is a theoretical model of computation using a tape, symbols, and a set of states.
• Any computing system equivalent to a Turing machine is considered Turing complete, meaning it can theoretically solve any computable problem.

Universal Turing Machine (UTM)

• A universal Turing machine (UTM) can simulate any other Turing machine by taking its instructions and input data and producing the same output.
• This highlights the powerful theoretical concept of a single machine capable of running any possible computation.

Computer Components

• A computer's main components include: memory, program counter, and the central processing unit (CPU).
• Memory stores both the program (instructions) and data (variables, constants, files).
• Program counter keeps track of the current instruction being executed.
• CPU contains the execution unit responsible for performing the computations specified by the program.

Turing Complete Instruction

• Surprisingly, a single instruction can be Turing complete and capable of implementing all programs.
• An example is the SBN (Subtract and Branch if Negative) instruction, which subtracts two numbers and branches to a different instruction if the result is negative.
• This simple instruction can be used to implement programs like adding a series of numbers using low-level programming.
• Assembly programs use low-level instructions like SBN, requiring more detailed understanding of the underlying hardware.

Modern ISAs

• Modern ISAs typically have multiple instructions, including:
  • Arithmetic instructions (add, subtract, multiply, divide)
  • Logical instructions (AND, OR, NOT)
  • Move instructions (transfer data between memory locations)
  • Branch instructions (implement conditional jumps based on memory values)
  • These instructions allow for implementing more complex programs with features like loops and conditional statements.

Practical Architecture Designs

• Two common practical machine architecture designs exist:
  • Harvard Architecture separates data memory and instruction memory, allowing for simultaneous access and potentially faster execution.
  • Von Neumann Architecture combines data and instruction memory, allowing for shared memory space.
• The main difference: how data and instructions are stored. Both architectures incorporate CPUs, input/output (I/O) devices, and communication pathways for data transfer.