What is a computer? Device capable of performing computations and making logical decisions at speeds of millions, and even billions of times faster than human beings can.
Computers process data under the control of sets of instructions called computer programs.
Hardware:
Devices that make up a computer system (keyboard, screen, disks, memory and processing units)
Software:
The computer programs that run on a computer
6 Logical Units or sections of a computer:
1. Input Unit – “receiving” section of the computer
- obtains information (data and computer programs) from various input devices and places this information at the disposal of the other units so that information may be processed.
- examples are; mouse, keyboard, joystick etc.
2. Output Unit – “shipping” section of the computer
- it takes information that has been processed by computers and places it on various output devices to make the information available for use outside of the computer
- printer, monitor etc.
3. Memory Unit – “warehouse” section of the computer
- retains information that has entered through the input unit so that the information may be made immediately available for processing when it is needed
4. Arithmetic and Logic Unit (ALU) – the “manufacturing” section of the computer
- responsible for performing calculations such as addition, subtractions, multiplication and division
- contains decision mechanisms that allow the computer to for example, compare two items from the memory unit to determine whether or not they are equal.
5. Central Processing unit (CPU) – “administrative” section of the computer
- responsible for supervising the operation of the other sections of the computer
6. Secondary Storage Units – programs that are not actively used by the other units are placed on secondary storage devices until they are again needed
- discs, cds, dvds, memory cards, zip drives, etc.
Evolution of Operating Systems
Single-User Batch Processing – computers used to be only capable of doing one task at a time
- takes a lot of time
Operating Systems – developed to make it more convenient to use computers
- there were smooth transitions between jobs
- this minimized the time it took for computers to switch between jobs, hence, increased the amount of work the computers could process
Multiprogramming – involves simultaneous operations of many jobs on the computer
Timesharing – users access the computers through terminals, typically devices with screens
- there are dozens, even hundred of users using the computer at once
- the computer actually does not do the tasks simultaneously, what the comp does is it runs a small portion of one user’s job and then moves to service the next user. The computer does this so quickly that it may provide service to each user several times per second. Thus, the user’s programs appear to be running simultaneously.
Personal Computing – 1977, Apple Computer popularized this phenomenon
- computers became economical enough for people to buy them for their own personal use
- in 1981, IBM introduced IBM personal computer
- but these stand-alone computers make it difficult to share information (sneakerets)
Distributed computing – networks connected via phone lines or Local Area Network (LAN)
- an organization’s computing, instead of being performed strictly at some central computer installation is distributed over networks to the sites at which the real work of the organization is performed
Client/Server Computing – servers – offer a common store of programs and data that may be used by client computers
Computer Languages:
Machine Languages – “natural language” of a particular computer
- hardware design of a computer
- generally consists of a string of numbers that instruct computers to perform their most elementary operations one at a time
+1300024789
+8090889299
+2089822245
Assembly Languages – programmers began using English-like abbreviations to represent the elementary operations of the computer.
- translator programs assemblers translate assembly languages to machine language at computer speeds
LOAD BASEPAY
ADD OVERPAY
STORE GROSSPAY
High-level languages – in which single statements could be written to accomplish substantial tasks
- translators of the high-level languages to machine language are called compilers
grossPay = basePay + overtimePay
- Visual Basic is the world’s most widely used high-level language
History of Visual Basic
BASIC – Beginner’s All-Purpose Symbolic Instruction Code
- was developed in the mid-1960’s by Professor John Kemeny and Thomas Kurtz of Darthmouth College as a language for writing simple programs,
- primary purpose was to help people program
- various types of computers led to many enhancements to the language
- with the development of Microsoft Window’s Graphical User Interface (GUI) in the late 1980’s and early 1990’s, the natural evolution of BASIC was Visual Basic which was created by Microsoft in 1991.
- There are currently 6 versions of Visual Basic
VB is running on Integrated Development Environment (IDE) which allows the programmer to create, run and debug Windows programs in one Application
