Hardware and Software;
The term 'software' refers to the set of electronic program instructions or data a computer
processor reads in order to perform a task or operation. In contrast, the term 'hardware' refers to
the physical components that you can see and touch, such as the computer hard drive, mouse,
and keyboard.
Software can be categorized according to what it is designed to accomplish. There are two main
types of software: systems software and application software.
Systems Software
Systems software includes the programs that are dedicated to managing the computer itself,
such as the operating system, file management utilities, and disk operating system (or DOS).
The operating system manages the computer hardware resources in addition to applications and
data. Without systems software installed in our computers we would have to type the instructions
for everything we wanted the computer to do!
Applications Software
Application software, or simply applications, are often called productivity programs or end-
user programs because they enable the user to complete tasks, such as creating documents,
spreadsheets, databases and publications, doing online research, sending email, designing
graphics, running businesses, and even playing games!
DATA HIERARCHY IN JAVA
A computer processes all data items as combinations of zeros and ones, because it is simple and
economical for engineers to build electronic devices that can assume two stable states—one
representing 0 and the other representing 1.
Bits
The smallest data item in a computer can assume the value 0 or the value 1. Such a data item is
called a bit (short for “binary digit”—a digit that can assume one of two values). Computer
circuitry performs various simple bit manipulations, such as examining the value of a bit, setting
the value of a bit and reversing the value of a bit (from 1 to 0 or from 0 to 1).
Characters
It is cumbersome for programmers to work with data in the low-level form of bits. Instead, they
prefer to work with data in such forms as decimal digits (0–9), letters (A–Z and a–z), and special
symbols (e.g., $, @, %, &, *, (, ), –, +, “, :, ? and / ). Digits, letters
and special symbols are known as characters. The computer’s character set is the set of all the
characters used to write programs and represent data items. Computers process only
1s and 0s, so a computer’s character set represents every character as a pattern of 1s and 0s.
Characters in Java are Unicode characters composed of two bytes, each composed of eight bits.
Java contains a data type, byte, that can be used to represent byte data.
Fields
Fields are composed of characters or bytes. A field is a group of characters or bytes that conveys
meaning. For example, a field consisting of uppercase and lowercase letters can be used to
represent a person’s name.
Records and Files
A record is a group of related fields. A file is a group of related records. A file contains arbitrary
data in arbitrary formats. In some operating systems, a file is viewed as a collection of byte.
Record Keys
To retrieval of specific records from a file, at least one field in each record is chosen as a record
key. A record key identifies a record as belonging to a particular person or entity and is unique to
each record.
Sequential Files
There are many ways to organize records in a file. The most common is called a sequential file,
in which records are stored in order by the record-key field.
Database
A group of related files is called a database.
A collection of programs designed to create and manage databases is called a database
management system (DBMS).
Computer Architecture is abstract model and are those attributes that are
visible to programmer like instructions sets, no of bits used for data,
addressing techniques.
A computer's organization expresses the realization of the architecture or
how features are implemented like these registers ,those data paths or this
connection to memory. contents of CO are ALU, CPU and memory and memory
organizations
EXAMPLE 1:
Suppose you are in a company that manufactures cars, design and all low-level
details of the car come under computer architecture (abstract, programmers
view), while making it’s parts piece by piece and connecting together the
different components of that car by keeping the basic design in mind comes
under computer organization (physical and visible).
Assembly Language
It is a low level programming language that allows a user to write a program using alphanumeric
mnemonic codes, instead of numeric codes for a set of instructions.
It requires a translator known as assembler to convert assembly language into machine language
so that it can be understood by the computer. It is easier to remember and write than machine
language.
Assembler – It is a computer program which converts or translates assembly language into
machine language. It assembles the machine language program in the main memory of the
computer and makes it ready for execution.
Advantages –
It is easy to understand and use
It is easy to locate and correct errors
It is easier to modify
Disadvantages –
It is machine dependant
High level Language
It is a machine independent language. It enables a user to write programs in a language which
resembles English words and familiar mathematical symbols. COBOL was the first high level
language developed for business.
Each statement in a high level language is a micro instruction which is translated into several
machine language instructions.
A compiler is a translator program which translates a high level programming language into
equivalent machine language programs. It compiles a set of machine language instructions for
every high level language program.
Source code: It is the input or the programming instructor of a procedural language.
The compiler translates the source code into machine level language which is known as object
code. Object code can be saved and executed as and when desired by the user.
Source Code → Language Translator Program → Object code
High level language → Machine level language
Linker: A program used with a compiler to provide links to the libraries needed for an
executable program. It takes one or more object code generated by a compiler and combines
them into a single executable program.
Interpreter: It is a translator used for translating high level language into the desired output. It
takes one statement, translates it into machine language instructions and then immediately
executes the result. Its output is the result of program execution.
Advantages of High level Language –
It is machine independent
It is easier to learn and use
It is easier to maintain and gives few errors
Disadvantages –
It lowers efficiency
It is less flexible
