This tutorial explains
1. C compiler.
2. Turbo C compiler.
3. Hexadecimal Number System.
4. Address Range represented in 20 bit.
5. Difference Between TSO and TSR program.
6. Difference between .com program and .exe program.
7. Memory cell.
8. Residence memory.
9. Physical Address.
10. Segmentation.
11. Offset Address.
12. Data segement.
C compiler
There are various c compilers are
variables. Some of these are:
S.N.
|
Name
|
Microprocessor
|
OS
|
1
|
Turbo c
3.0
|
8086
|
MS DOS
|
2
|
ANSIC C
|
80386
|
LINUX
|
3
|
Borland
C 4.0
|
80386
|
WINDOW
|
4
|
Microsoft
C
|
8086
|
MS DOS
|
5
|
Visual
C++
|
80386
|
WINDOW
|
Note: 8086 is 16 bit
microprocessor while 80386 is 32 bit microprocessor.
Note: Different versions of compilers
are based on the different microprocessors and support many OS. It is always
changing. As a programmer you should know the microprocessor name, its world
length etc. which your compiler is based on. Since c language is platform
dependent. In preprocessor section you will know how to make a program as much
as platform independent.
Turbo c compiler
Turbo c is an IDE of c
programming language created by Borland. Turbo C 3.0 is based on MS DOS
operation system. It is one of the most popular c compilers. It
uses 8086 microprocessor which is 16 bit microprocessor. It has 20 address
buses and 16 data bus. Its word length is two byte.
Size of data types in Turbo C 3.0:
Data type
|
Size
|
short
int
|
2
|
int
|
2
|
long
int
|
4
|
char
|
1
|
float
|
4
|
double
|
8
|
long
double
|
10
|
Byte ordering : Little Endianness
Default pointer : Near
Default memory model : Small
To compile a c program: Alt + F9
To run a c program: Ctrl + F9
Turbo C 4.5 is based on Microsoft window operating
system. It is 32 bit compilers.
Size of
data type in Turbo C 4.5:
Data type
|
Size (Byte)
|
short
int
|
2
|
int
|
4
|
long
int
|
4
|
char
|
1
|
float
|
4
|
double
|
10
|
long
double
|
12
|
Default pointer: Far
Default memory model: Compact
Hexadecimal representation in c
In hexadecimal number system we use 16 different
digits so its base is 16. List of all hexadecimal digits:
Hexadecimal digit
|
Decimal equivalent
|
Binary equivalent
|
0
|
0
|
0000
|
1
|
1
|
0001
|
2
|
2
|
0010
|
3
|
3
|
0011
|
4
|
4
|
0100
|
5
|
5
|
0101
|
6
|
6
|
0110
|
7
|
7
|
0111
|
8
|
8
|
1000
|
9
|
9
|
1001
|
A
|
10
|
1010
|
B
|
11
|
1011
|
C
|
12
|
1100
|
D
|
13
|
1101
|
E
|
14
|
1110
|
F
|
15
|
1111
|
To convert the binary number into
hexadecimal number:
Make the
group of four binary digits from right to left and replace the four binary
digits with the equivalent hexadecimal digit using above table.
For
example:
Binary
number = 11000111110101
Group of four digits from right
side:
to make
group of four digit of left most digit 11 , add two zero at the left side
i.e. 0011
Now put
or replace with it the equivalent hexadecimal digit using above table
So,
equivalent hexadecimal number will be 31F5.
What will be address range which can be represented
in 20 bit?
|
Binary
|
Hexadecimal
|
Min
possible
|
0000 0000 0000 0000 0000
|
00000
|
Max
possible
|
1111 1111 1111 1111 1111
|
FFFFF
|
In c any
hexadecimal number start with 0x 0r 0X So, address range will be 0x00000
to 0xFFFFF. So in turbo C 3.0 memory address of all variables must be within
0x00000 to oxFFFFF.
It is 1MB memory range.
Note.
2^10 = 1KB
2^20 = 1MB
2^30 = 1GB
Where 10, 20, 30 are number of
bit.
Difference between TSR and TSO program
Difference
between TSR and TSO program
TSO means
terminate but stay outside. It is that program, which release the main memory
after the execution of the program. Example ms paint, notepad, turbo c
compilers etc.
TSR means
terminate but stay residence .It is those program, which after the execution of
the program does not release the RAM (main memory).e.g. antivirus.
Difference between .com program and .exe program in
c programming language
Both .com and .exe program are executable program
but .com program execute faster than .exe program. All drivers are .com
program. .com file has higher preference than .exe
For example:
Open the command prompt in window OS. (Type CMD in Run)
In the command prompt type notepad and press enter key you will
get the notepad. Since it executes notepad.exe
Repeat the same task but now first create any .com file in the same
working directory. We can create it as open the notepad save it as notepad.com,
set save as type is All files or we can create the .com file from command
prompt.
Then type notepad in command prompt and press the enter key you will get
error message like:
C:\notepad.com is not a valid Win32 application.
It proves that .com has higher precedence than
.exe program.
Com file is binary execute used in MS DOS. Com
program keeps only code and data. It stores code and data in one
segment. In Turbo C memory model should tiny to create .com program. We
will discuss later how to create .com file in in turbo c.
Memory cell in computer
Entire
RAM has divided in numbers of equal parts, which are
known as
memory cells. Following diagram represents the 256
MB RAM.
Each cell
can store one-byte data. Data are stored in the
binary number system. That is a
character data reserves one
memory cell while floating data
reserves four memory cells.
Each
memory cell has unique address. Address is always in
whole number and must be in
increasing order. We will discuss
how a characters, integers etc.
data are in stored in the
data type chapter. Just for now
assume
int a = 4;
Here
variables a stores in the memory in the flowing way:
If you
know memory address of first cell is 0x5000 then
what would be the memory address
of next memory cell?
It will
5001 since integer data always stores at
continuous memory location and as
we know memory address
always in increasing order.
What is residence memory in c programming language?
RAM has divided into two parts:
(1)
Extended memory (useless)
(2)
Residence memory
In Turbo C 3.0 compiler size of
residence memory is 1MB.
Residence memory:
When any
program is executed it is stored in the
residence memory. For turbo c
3.0, it has 1MB residence
memory i.e. when we open turbo c
3.0 it stores 1MB in the
RAM.
Segmentation in operating system
Segmentation in c programming language
Residential
memory of RAM of size 1MB has divided into 16
equal parts. These parts is
called segment. Each segment
has size is 64 KB.
16 * 64 KB = 1 MB
This process of division is known as segmentation.
Note: In
turbo c 3.0 physical addresses of any variables
are
stored in the 20 bits. But we have not any pointers
(We will
discuss later what is pointer?)of size 20 bits.
So
pointers cannot access whole residence memory
address.To
solve this problem we there are three types
pointers in
c language. They are
1. Near pointer
2. Far pointer
3. Huge pointer
Data segment in c
All the segments are used
for specific purpose. Like segment number 15 is used for ROM, segment number 14
is used for BIOS etc.
We will discuss about how to access text video
memory, graphics video memory in the pointer and union chapters of 255 bits
color graphics programming.
Segment number eight has special name which is known
as data segment. This segment has been divided into four parts. This is very
important for c programming
1. Stack area
All automatic variables and constants are stored
into stack area. Automatic variables and constants in c:
1.
All the local variables of default storage
class.
2.
Variables of storage calls auto.
3.
Integer constants, character constants, string
constants, float constants etc in any expression.
4.
Function parameters and function return value.
Variables in the stack area are always deleted when
program control reaches it out of scope. Due to this stack area is also called
temporary memory area. For example:
What will be output of
following c code?
#include
int main(){
int i;
for(i=0;i<3;i++){
int a=5;
printf("%d",a);
}
return 0;
}
Output:
5 5 5
Explanation:
Since variable a is automatic
variable, it will store in the stack area. Scope of variable a is within for loop. So after each
iteration variable a will be deleted from stack and in each iteration variable
a will initialize.
This two concepts are only for Turbo C 3.0
It follows LIFO data structure. That in the stack
area of memory data is stored in last in first out. For example:
What will be output of
flowing c code. (Turbo c 3.0)?
#include
int main(){
int a =5, b = 6, c = 7,d =8;
printf("%d %d %d");
return 0;
}
Output: 8 7 6
Explanation:
Default storage class of variables a, b, c and d is
auto .Since it automatic variable it will be sorted in the stack area of memory.
It will store in the stack as
Stack always follows LIFO data structure. In the
printf function, name of variables is not written explicitly. So default output
will content of stack which will be in the LIFO order i.e. 8 7 6.
It has two part one for initialize variable another
for non-initialize variable. All initialize variables are more nearer than not initialized
variable and vice versa. For example:
What will be output of
following program (Turbo c 3.0)?
#include
int main(){
int a =5, b, c =7;
printf("%d %d %d");
return 0;
}
Output: 7 5 garbage value
Explanation:
Automatic variable a and c has initialized while b
has not initialized. Initialize variables are more nearer than uninitialized
variable .They will be stored in the stack. So due to LIFO first output will be
7 then 6 (since a is more nearer than b with respect to c) then any garbage
value will be output which is present in the stack.
Note: Default storage class
of any local variable is auto.
2. Data area:
All static and extern variable are stored in the
data area. It is permanent memory space and variable will store in the memory unless
and until program end. For example:
What will be output of
following c code?
#include
int main(){
int i;
for(i=0;i<3;i++){
static int a=5;
printf("%d",a);
}
return 0;
}
Output: 5 6 7
3. Heap area:
This memory area is use to allocate memory
dynamically. In c we can allocate the memory space dynamically by using
function malloc and calloc. It always allocates memory in the heap area. Its
size is variable and depends upon free space in the memory.
4. Code area:
Function pointer can only access code area. Size of
this area is always fixed and it is read only memory area.
It is also called as 'Procedure oriented programming language. 
