Hardware and software

Rer

Logical unit

Sections in which computers are technically divided into:

Input unit

Storages (Primary & secondary)

Output unit

Control unit

Arithmetic logic unit

Input unit

Receiving section, it can receive anything from external devices, scanning images or secondary storage devices as well. 

Output unit

Transfers the taken information onto output devices, mostly screens, but applies to many devices.

Memory unit

Rapid access, lower capacity “warehouse” that stores information from input unit or processed info ready for output. Also called primary memory or RAM, volatile and disappears when computer is turned off. 

Arithmetic and logic unit

Manufacturing section that performs calculations, also compares and decides whether two items in memory are equal.

CPU Central Processing unit

Coordinates and supervises actions of the other sections. Tells when input should go to memory, when memory should be processed by ALU, etc.

Multicore processors

Computers have more than one processors to multitask directions. Some have dual-core processors, and others quad-core processors.

Secondary storage unit

Long term high capacity warehouse section. Stores programs and data not actively used. Information is persistent, takes longer to access, but its cost per unit is lesser.

Data Hierarchy

File

Record

Field

Character/Byte

Bit

Machine language

Understandable by computers, generally consists of numbers reduced to 1s and 0s.

Assembly languages

Made with english abbreviations for programmers to understand and work with better.

Translator programs/Assemblers

Developed to convert assembly language to machine language.

High-level language

Substantial tasks are accomplished in a single statement.

Use everyday English and common math expressions.

Compilers

Translator programs for high-level languages to machine languages.

Interpreter

Program that executes high-level language programs directly, although slower than compiler programs.

Scripting languages

Interpreted from source code directly, no need for compiling, can execute directly. Control applications and used in automation. They are processed by interpreters.

Examples: JavaScript, Python and PHP

C facts

Evolved from B by Dennis Ritchie

Implemented in 1972

Development language of UNIX operating system

Is mostly hardware independent

C programs are portable to most computers usually.

C standard library

C programs consist of pieces called functions, programmers take advantage of a rich collection of existing functions names the standard library.

Parts of C systems

Program development environment 

Language

C Standard Library

C program phases

Edit, process, compile, link, load, execute

Linker

During the linking phase, holes are created in the code due to functions being defined/referenced elsewhere such as standard libraries. A linker links the object code with code from missing functions to create an executable image.

gcc

Command to compile and link a program in linux system (GNU compiler)

Execute command

./a.out

Editing

Creating code in the editing program, also where you make corrections, then store it.

Preprocessing a C program

Compiler translates the c program into machine language code.

In C, preprocessor executes automatically before compiler translation, includes other files in file and text replacements.

Compiling a C program

Where the compiler does its job of translating, you may get a syntax/compile error when something is written wrong.

Linking

Linker creates an executable image when there are “holes” in program created by references to functions defined elsewhere (other libraries).

Loading

Program, and other additional components from library are placed in memory before being executed.

Done by loader, which takes executable image from disk to memory.

Execution

Actually running the program.