Basic types of web attacks

What are the two basic types of attacks?(Choose two.)

A. DoS

B. Passive 

C. Sniffing 

D. Active 

E. Cracking

Answer: B, D

Explanation: Passive and active attacks are the two basic types of attacks. 

Who is an Ethical Hacker?

A. A person whohacksfor ethical reasons

B. A person whohacksfor an ethical cause

C. A person whohacksfor defensive purposes 

D. A person whohacksfor offensive purposes

Answer: C 

Explanation: The Ethical hacker is a security professional who applies his hacking skills for defensive purposes. 

Step by Step method to create a new partition from the Current partition

step 1 goto control; panel
step 2 then select administrative tools
step 3 then select computer management
step 4 select disk management under storage , it will show your hard disk now  select the  hard disk right  click on it. and select  shrink volume.
step 5  now type  in the  amount of  space  you  want  from the  disk .and  click on  shrink. the  space obtained  after  will be  unallocated space.
step 6 now  right  click on the unallocated  space  and select  new  simple  volume .
           just  follow the wizard. and  you  will get  the  new  partitiion

1617 - John Napier creates “Napier’s Bones,” wooden or ivory rods used for calculating.

What is "Hacktivism"?

A. Hacking for a cause

B. Hacking ruthlessly

C. An association which groups activists 

D. None of the above

Answer: A

Explanation: The term was coined by author/critic Jason Logan Bill Sack in an article about media artist Shu Lea Cheang. Acts of hacktivism are carried out in the belief that proper use of code will have leveraged effects similar to regular activism or civil disobedience. 

What does the term "Ethical Hacker" mean?

A. Someone who is hacking for ethical reasons.

B. Someone who is using his/her skills for ethical reasons.

C. Someone who is using his/her skills for defensive purposes. 

D. Someone who is using his/her skills for offensive purposes.

Answer: C

Explanation: Ethical hacking is only about defending your self or your employer against malicious persons by using the same techniques and skills. 

What is the essential difference between an 'Ethical Hacker' and a 'Cracker'?

What is the essential difference between an 'Ethical Hacker' and a 'Cracker'?

A. The ethical hacker does not use the same techniques or skills as a cracker. 

B. The ethical hacker does it strictly for financial motives unlike a cracker. 

C. The ethical hacker has authorization from the owner of the target.

D. The ethical hacker is just a cracker who is getting paid.

Answer: C

Explanation: The ethical hacker uses the same techniques and skills as a cracker and the motive is to find the security breaches before a cracker does. There is nothing that says that a cracker does not get paid for the work he does, a ethical hacker has the owners authorization and will get paid even if he does not succeed to penetrate the target. 

A to Z DOS Commands

An A to Z Index of the Windows command line

ADDUSERS Add or list users to/from a CSV file
ARP Address Resolution Protocol
ASSOC Change file extension associations•
ASSOCIAT One step file association
ATTRIB Change file attributes
b
BOOTCFG Edit Windows boot settings
BROWSTAT Get domain, browser and PDC info
c
CACLS Change file permissions
CALL Call one batch program from another•
CD Change Directory - move to a specific Folder•
CHANGE Change Terminal Server Session properties
CHKDSK Check Disk - check and repair disk problems
CHKNTFS Check the NTFS file system
CHOICE Accept keyboard input to a batch file
CIPHER Encrypt or Decrypt files/folders
CleanMgr Automated cleanup of Temp files, recycle bin
CLEARMEM Clear memory leaks
CLIP Copy STDIN to the Windows clipboard.
CLS Clear the screen•
CLUSTER Windows Clustering
CMD Start a new CMD shell
COLOR Change colors of the CMD window•
COMP Compare the contents of two files or sets of files
COMPACT Compress files or folders on an NTFS partition
COMPRESS Compress individual files on an NTFS partition
CON2PRT Connect or disconnect a Printer
CONVERT Convert a FAT drive to NTFS.
COPY Copy one or more files to another location•
CSCcmd Client-side caching (Offline Files)
CSVDE Import or Export Active Directory data
d
DATE Display or set the date•
DEFRAG Defragment hard drive
DEL Delete one or more files•
DELPROF Delete NT user profiles
DELTREE Delete a folder and all subfolders
DevCon Device Manager Command Line Utility
DIR Display a list of files and folders•
DIRUSE Display disk usage
DISKCOMP Compare the contents of two floppy disks
DISKCOPY Copy the contents of one floppy disk to another
DISKPART Disk Administration
DNSSTAT DNS Statistics
DOSKEY Edit command line, recall commands, and create macros
DSACLs Active Directory ACLs
DSAdd Add items to active directory (user group computer)
DSGet View items in active directory (user group computer)
DSQuery Search for items in active directory (user group computer)
DSMod Modify items in active directory (user group computer)
DSMove Move an Active directory Object
DSRM Remove items from Active Directory
e
ECHO Display message on screen•
ENDLOCAL End localisation of environment changes in a batch file•
ERASE Delete one or more files•
EVENTCREATE Add a message to the Windows event log
EXIT Quit the current script/routine and set an errorlevel•
EXPAND Uncompress files
EXTRACT Uncompress CAB files
f
FC Compare two files
FIND Search for a text string in a file
FINDSTR Search for strings in files
FOR /F Loop command: against a set of files•
FOR /F Loop command: against the results of another command•
FOR Loop command: all options Files, Directory, List•
FORFILES Batch process multiple files
FORMAT Format a disk
FREEDISK Check free disk space (in bytes)
FSUTIL File and Volume utilities
FTP File Transfer Protocol
FTYPE Display or modify file types used in file extension associations•
g
GLOBAL Display membership of global groups
GOTO Direct a batch program to jump to a labelled line•
GPUPDATE Update Group Policy settings
h
HELP Online Help
i
iCACLS Change file and folder permissions
IF Conditionally perform a command•
IFMEMBER Is the current user in an NT Workgroup
IPCONFIG Configure IP
k
KILL Remove a program from memory
l
LABEL Edit a disk label
LOCAL Display membership of local groups
LOGEVENT Write text to the NT event viewer
LOGOFF Log a user off
LOGTIME Log the date and time in a file
m
MAPISEND Send email from the command line
MBSAcli Baseline Security Analyzer.
MEM Display memory usage
MD Create new folders•
MKLINK Create a symbolic link (linkd)
MODE Configure a system device
MORE Display output, one screen at a time
MOUNTVOL Manage a volume mount point
MOVE Move files from one folder to another•
MOVEUSER Move a user from one domain to another
MSG Send a message
MSIEXEC Microsoft Windows Installer
MSINFO Windows NT diagnostics
MSTSC Terminal Server Connection (Remote Desktop Protocol)
MUNGE Find and Replace text within file(s)
MV Copy in-use files
n
NET Manage network resources
NETDOM Domain Manager
NETSH Configure Network Interfaces, Windows Firewall & Remote access
NETSVC Command-line Service Controller
NBTSTAT Display networking statistics (NetBIOS over TCP/IP)
NETSTAT Display networking statistics (TCP/IP)
NOW Display the current Date and Time
NSLOOKUP Name server lookup
NTBACKUP Backup folders to tape
NTRIGHTS Edit user account rights
o
OPENFILES Query or display open files
p
PATH Display or set a search path for executable files•
PATHPING Trace route plus network latency and packet loss
PAUSE Suspend processing of a batch file and display a message•
PERMS Show permissions for a user
PERFMON Performance Monitor
PING Test a network connection
POPD Restore the previous value of the current directory saved by PUSHD•
PORTQRY Display the status of ports and services
POWERCFG Configure power settings
PRINT Print a text file
PRNCNFG Display, configure or rename a printer
PRNMNGR Add, delete, list printers set the default printer
PROMPT Change the command prompt•
PsExec Execute process remotely
PsFile Show files opened remotely
PsGetSid Display the SID of a computer or a user
PsInfo List information about a system
PsKill Kill processes by name or process ID
PsList List detailed information about processes
PsLoggedOn Who's logged on (locally or via resource sharing)
PsLogList Event log records
PsPasswd Change account password
PsService View and control services
PsShutdown Shutdown or reboot a computer
PsSuspend Suspend processes
PUSHD Save and then change the current directory•
q
QGREP Search file(s) for lines that match a given pattern.
r
RASDIAL Manage RAS connections
RASPHONE Manage RAS connections
RECOVER Recover a damaged file from a defective disk.
REG Registry: Read, Set, Export, Delete keys and values
REGEDIT Import or export registry settings
REGSVR32 Register or unregister a DLL
REGINI Change Registry Permissions
REM Record comments (remarks) in a batch file•
REN Rename a file or files•
REPLACE Replace or update one file with another
RD Delete folder(s)•
RMTSHARE Share a folder or a printer
ROBOCOPY Robust File and Folder Copy
ROUTE Manipulate network routing tables
RUNAS Execute a program under a different user account
RUNDLL32 Run a DLL command (add/remove print connections)
s
SC Service Control
SCHTASKS Schedule a command to run at a specific time
SCLIST Display NT Services
SET Display, set, or remove environment variables•
SETLOCAL Control the visibility of environment variables•
SETX Set environment variables permanently
SFC System File Checker
SHARE List or edit a file share or print share
SHIFT Shift the position of replaceable parameters in a batch file•
SHORTCUT Create a windows shortcut (.LNK file)
SHOWGRPS List the NT Workgroups a user has joined
SHOWMBRS List the Users who are members of a Workgroup
SHUTDOWN Shutdown the computer
SLEEP Wait for x seconds
SLMGR Software Licensing Management (Vista/2008)
SOON Schedule a command to run in the near future
SORT Sort input
START Start a program or command in a separate window•
SU Switch User
SUBINACL Edit file and folder Permissions, Ownership and Domain
SUBST Associate a path with a drive letter
SYSTEMINFO List system configuration
t
TASKLIST List running applications and services
TASKKILL Remove a running process from memory
TIME Display or set the system time•
TIMEOUT Delay processing of a batch file
TITLE Set the window title for a CMD.EXE session•
TLIST Task list with full path
TOUCH Change file timestamps
TRACERT Trace route to a remote host
TREE Graphical display of folder structure
TYPE Display the contents of a text file•
u
USRSTAT List domain usernames and last login
v
VER Display version information•
VERIFY Verify that files have been saved•
VOL Display a disk label•
w
WHERE Locate and display files in a directory tree
WHOAMI Output the current UserName and domain
WINDIFF Compare the contents of two files or sets of files
WINMSD Windows system diagnostics
WINMSDP Windows system diagnostics II
WMIC WMI Commands
x
XCACLS Change file and folder permissions
XCOPY Copy files and folders

Keyboard Shortcuts for MS-Word

Ctrl+Shift+Up Arrow : Select to the Beginning of the paragraph

Ctrl+Shift+END : Select to the End of the Document

Ctrl+Shift+HOME : Select to the Beginning of the Document

Ctrl+Shift+> : Increase Font Size

Ctrl+Shift+D : Double Underline the selected document

Alt+Shift+D : Insert Date Field at current insertion location

Ctrl+G : Go to option

Ctrl+F : Find

Ctrl+J : Justified Align

Alt+F10 : To Maximize Window

Ctrl+F2 : Print Preview

Shift+F3 : Change Case

Shift+F7 : Thesaurus

Ctrl+Shift+F12 : To Print

Ctrl+P : To Print

F3 : Autotext insertion

F4 : Repetition of Last Action (Repeat Last Command)

F8 : To Extend Selection

Computer startup process

The PC start-up process 

When you turn power on, several things happen in the PC:
●   You hear the fan motor starting. There are one or more cooling fans in the PC. They produce a whirring sound.
●   After a few seconds, text starts to scroll on the screen.
●   Now the PC tests and counts the RAM. You see a number on the screen. It increases in size.
●   To understand the working of the PC, it is useful to study the PC start-up process. Those are events, which take place from power-on until the PC is ready to work. Remember, the PC can do nothing without receiving instructions. These instructions are commands, which are sent to the CPU. During start-up, the PC reads the commands in this sequence:
●    First it receives commands from the ROM chips. Those chips are inherent in any computer. They contain the POST and BIOS instructions, which we will look at shortly.
●   Next, the operating system is read from the hard disk (or from floppy drive A). This is called the boot process.

The ROM chips 

ROM (Read Only Memory). The ROM chips are on the system board. They contain. system software. System software are instructions, which enable the PC to coordinate the functions of various computer components. The ROM chips contain instructions, which are specific for that particular system board. Those instructions will remain in the PC throughout its life. They will usually not be altered. Primarily, they are start-up instructions. There are different parts in the start-up instructions. For most users, they are all woven together. You can differentiate between:
●   POST (Power On Self Test)
●   The Set-up instructions, which connect with the CMOS instructions
●   BIOS instructions, which connect with the various hardware peripherals
●   The Boot instructions, which calls the operating system (DOS, OS/2, or Windows)
  All these instructions are in ROM chips, and they are activated on by one during start-up. Let us look at each part.

POST

Power On Self Test is the first instruction executed during start-up. It checks the PC components and that everything works. You can recognize it during the RAM test, which occurs as soon as you turn power on. As users, we have only limited ability to manipulate the POST instructions. But certain system boards enable the user to order a quick system check. Some enable the user to disable the RAM test, thereby shortening the duration of the POST. The duration of the POST can vary considerably in different PC's. On the IBM PC 300 computer, it is very slow. But you can disrupt it by pressing [Esc]. If POST detects errors in the system, it will write error messages on the screen. If the monitor is not ready, or if the error is in the video card, it will also sound a pattern of beeps (for example 3 short and one long) to identify the error to the user. If you want to know more of the beeps, you can find explanations on the Award, AMI and Phoenix web sites. POST also reads those user instructions, which are found in CMOS:

CMOS

CMOS (Complimentary Metal Oxide Semiconductor) is a small amount of memory in a special RAM chip. Its memory is maintained with electric power from a small battery. Certain system data are stored in this chip. They must be read to make the PC operable. There may be 100 to 200 bytes of data regarding date, time, floppy and hard disk drives, and much more. CMOS data can be divided in two groups: 

●   Data, which POST can not find during the system test.

●   Data, which contain user options. 

 For example, POST cannot by itself find sufficient information about the floppy drive(s). Floppy drives are so "dumb," that POST cannot read whether they are floppy drives or not, nor what type. About the same goes for IDE hard disks, while EIDE hard disks are a little more "intelligent," However, POST still needs assistance to identify them 100% correctly. The same goes for RAM: POST can count how much RAM is in the PC. However, POST cannot detect whether it is FPM, EDO or SD RAM. Since the CPU and BIOS reads data from RAM chips differently, depending on the RAM type, that type must be identified. 

Suppliers of system software 

All PC's have instructions in ROM chips on the system board. The ROM chips are supplied by specialty software manufacturers, who make BIOS chips. The primary suppliers are: 

●  Phoenix

●   AMI (American Megatrends)

●   Award

   You can read the name of your BIOS chip during start-up. You can also see the chip on the system board.

The Setup program 

You communicate with the BIOS programs and the CMOS memory through the so-called Setup program. Typically you reach the Setup program by pressing [Delete] immediately after you power up the PC. That brings you to a choice of setup menus. You leave Setup by pressing [Esc], and choose "Y" to restart the PC with the new settings. Generally, you should not change these settings, unless you know precisely what you are doing. The Setup program can do many things for you. You have to enter Setup, if you install a different type or additional disk drive in your PC. Certain BIOS's will also need adjustment of its settings, if a CD ROM drive is installed on one of the EIDE channels. 

Modifying the boot sequence 

You can change the boot sequence from A:, C: to C:, A:. That means, that the PC will not try to boot from any diskette in the A drive. That will protect you from certain virus attacks from the boot sector. Also, the boot process will not be blocked by any diskette in the A drive. If you need to boot from A-drive (for example, if you want to install Windows 97 ), you have to enter Set-up again, and change the boot sequence to A:, C:. That is no problem. 

Power Management

You also use the Setup program to regulate Power Management, which is the power saving features in the system board. For example, you can make the CPU shut down after one minute of no activity. There are plenty of settings available in this area. 

Password Protection 

You protect the Setup program with a password. This is used widely in schools, where they do not want the little nerds to make changes in the setup. Please remember the password (write it down in the mainboard manual). If you forget it you have to remove the battery from the mainboard. Then all user-input to the CMOS is erased - including the password.

The BIOS programs

During start-up. the BIOS programs are read from a ROM chip. BIOS is abbreviation of Basic Input Output System and those are programs, which are linked to specific hardware systems. For example, there is a BIOS routine, which identifies how the PC reads input from the keyboard. BIOS is a typical link in the IBM compatible PC design. The BIOS programs control hardware, the user (programmer) controls hardware via a call to BIOS. BIOS typically occupy 1 MB, and the programs are saved ROM chips on the system board. During start-up, BIOS is read from ROM chips. That information is supplemented with the system data saved in CMOS. Furthermore, there is BIOS code on the expansion cards. The expansion cards are external hardware, as interpreted by the system board, and the BIOS code, which is linked to the expansion card, must be included in the configuration. Therefore, this expansion card ROM is read during start-up, and the program code is woven together with other BIOS data. It is all written into RAM, where it is ready for the operating system,

BIOS-update 

BIOS programs can be updated. The modern system board has the BIOS instructions in flash-ROM, which can be updated. You can get new BIOS-software from your supplier or on the Internet, which can be read onto the system board. The loading is a special process, where you might need to change a jumper switch on the system board. Usually, you do not need to do this, but it is a nice available option.

ATX

The latest PC electronic standard is called ATX. It consists of a new type system board with a specific physical design smaller than the traditional board (30.5 cm X 19 cm). The I/O connectors COM1, COM2 and LPT, keyboard, mouse and USB are mounted directly on the system board. The ATX board requires specifically designed chassis's with an I/O access opening measuring 1¾ by 6¼ inch. ATX is designed by Intel, but has gained general acceptance. The ATX system board is more ”intelligent” than the ordinary type. In a few years, it will be wide spread. It includes advanced control facilities, where the BIOS program continually checks the CPU temperature and voltages, the cooling fans RPM, etc. If over heating occurs, the PC will shut down automatically. The PC can also be turned on by for example modem signals, since the power supply is controlled by the system board. The on/off button will turn the PC "down" without turning it completely off. If you want a PC designed for the future, the ATX layout is what you should go for.

Computer Hardware

Data exchange - the Mainboard Or Motherboard

It is a printed circuit board, on which multiple chips, ports (plug ins), and other electronic components are mounted. In the PC, data are exchanged continuously between these components. Therefore it is important to understand each component, its connections and characteristics. All data exchange is done on the system board, which thus is the most important component in the PC. So, now we will start with a more technical evaluation of the system board.

The motherboard components

The PC is built around the main, system or mother board (all meaning the same). This board is so essential for the PC, because it holds the CPU and all its connections. Let us see, what you can find on it:
●    ROM-chips with BIOS and other programs
●   CMOS, storing system setup data
●   The CPU
●   L2-cache
●   RAM (Random Access Memory) mounted in SIMM or DIMM chips
●   Chip sets with I/O controllers
●   Cards to connect with keyboard and mouse
●   Serial and parallel ports
●   Connectors to disk drives and EIDE drive (hard disk, CD-ROM etc.)
●   Slots for expansion cards
●   Jumpers to adjust voltage, system bus speed, clock, etc.
●   Contacts to reset HD activity, speaker, etc.

ASCII

ASCII

ASCII means American Standard Code for Information Interchange. It is an industry standard, which assigns letters, numbers, and other characters within the 256 slots available in the 8 bit code.

The ASCII table is divided in 3 sections:

●    Non printable system codes between 0 and 31.

●   "Lower ASCII" between 32 and 127. This part of the table originates from older, American ADP systems, which work d on 7 bit character tables. Foreign letters, like Ø and Ü were not available then.

●   "Higher ASCII" between 128 and 255. This part is programmable, in that you can exchange characters, based on which language you want to write in. Foreign letters are placed in this part.

An example

Let us imagine a stream of bits sent from the keyboard to the computer. When you type, streams of 8 bits are sent to the computer.
Let us look at a series of bits: 001100010011001000110011
Bits are combined into bytes (each 8 bits). These 24 bits are interpreted as three bytes. Let us read them as bytes: 00110001, 00110010, and 00110011.
When we convert these byte binary numbers to decimal numbers, you will see that they read as 49, 50, and 51 in decimal numbers. To interpret these numbers, we have to look at the ASCII table. You will find that you have typed the numbers 1, 2, and 3.

Computer Basics

Introduction to the PC   

The technical term for a PC is micro data processor. That name is no longer in common use. However, it places the PC in the bottom of the computer hierarchy:

●  Mainframes are the very largest computers - million dollar machines, which can occupy more than one room, An example is IBM model 390. 

●  Minicomputers are large powerful machines. They typically serve a network of simple terminals. IBM's AS/400 is an example of a minicomputer.

●  Workstations are powerful user machines. They have the power to handle complex engineering applications. They use the UNIX or sometimes the NT operating system. Workstations can be equipped with powerful RISC processors like Digital Alpha or MIPS. 

●   PC's are the smallest in this order: Small inexpensive, mass produced computers. They work on DOS, Windows, or similar operating systems. They are used for standard applications.

The PC's success 

The PC came out in 1981. In less than 20 years, it has totally changed our means of communicating. When the PC was introduced by IBM, it was just one of many different micro data processors. However, the PC caught on. In 5-7 years, it conquered the market. From being an IBM compatible PC, it became the standard.

If we look at early PC's, they are characterized by a number of features. Those were instrumental in creating the PC success. 

●   The PC was from the start standardized and had an open architecture.

●   It was well documented and had great possibilities for expansion.

●   It was inexpensive, simple and robust (definitely not advanced).   

The PC started as IBM's baby. It was their design, built over an Intel processor (8088) and fitted to Microsoft's simple operating system MS-DOS. 

Since the design was well documented, other companies entered the market. They could freely copy the central system software (BIOS) and the ISA bus, since they were not patented. Slowly, a myriad of companies developed, manufacturing IBM compatible PC's and components for them. 

The PC construction 

The PC consists of a central unit (referred to as the computer) and various peripherals. The computer is a box, which contains most of the working electronics. It is connected with cables to the peripherals. Here is a list of the PC components.

Components in the central unit - the computer                                                        

The main board:    

CPU, RAM, cache,   ROM chips with BIOS and start-up programs.                          

Chip sets (controllers). Ports, busses and expansion slots.Monitor                      

Drives:    

Hard disk(s), floppy drive(s), CD-ROM, etc.                                                             

                                                                                                                                      

Expansion cards:                                                                                

Graphics card (video adapter), network controller, SCSI controller.                                

Sound card, video and TV card. Internal modem and ISDN card                            

Peripherals                                                                                                                             
External modem  

Printer
Keyboard and mouse                                                                                                          
Scanner  
Tape drives, etc.  

History of the PC

Computers have their roots 300 years back in history. Mathematicians and philosophers like Pascal, Leibnitz, Babbage and Boole made the foundation with their theoretical works. Only in the second half of this century was electronic science sufficiently developed, to make practical use of their theories. The modern PC has roots back to USA in the 1940's. Among the many scientists, I like to remember John von Neumann (1903-57). He was a mathematician, born in Hungary. We can still use his computer design today. He broke computer hardware down in five primary parts:
●  CPU
●   Input
●   Output
●   Working memory
●   Permanent memory   Actually, von Neumann was the first to design a computer with a working memory (what we today call RAM). If we apply his model to current PC's, it will look like this:

                                                                                                                    

About data 

Our PC's are data processors. PC's function is simple: to process data, and the processing is done electronically inside the CPU and between the other components. That sounds simple, but what are data, and how are they processed electronically in a PC? 

Analog data 

The signals, which we send each other to communicate, are data. Our daily data have many forms: sound, letters, numbers, and other characters (handwritten or printed), photos, graphics, film. All these data are in their nature analog, which means that they are varied in their type. In this form, they are unusable in a PC. The PC can only process concise, simple data formats. Such data can be processed very effectively. 

Digital data 

The PC is an electric unit. Therefore, it can only deal with data, which are associated with electricity. That is accomplished using electric switches, which are either off or on. You can compare with regular household switches. If the switch if off, the PC reads numeral 0. If it is on, it is read as numeral one.
The PC is filled with these switches (in the form of transistors). There are literally millions of those in the electronic components. Each represents either a 0 or a 1, so we can process data with millions of 0's and 1's.

Bits

Each 0 or 1 is called a bit. Bit is an abbreviation of the expression BInary digiT. It is called binary, since it is derived from the binary number system:

0 Equals to one bit

1 Equals to one bit

0110 Equals to 4 bit

01101011 Equals to 8 bit

The binary number system 

The binary number system is made up of digits, just like our common decimal system (10 digit system). But, while the decimal system uses digits 0 through 9, the binary system only uses digits 0 and 1. If you are interested in understanding the binary number system, then here is a brief course. Try if you can follow the system. See how numbers are constructed in the binary system, using only 0's and 1's:

Numbers, as known                       Same numbers in binary system
in the decimal-system                        
                                                                           
0                                                                      0
1                                                                      1
2                                                                     10
3                                                                     11
4                                                                    100
5                                                                    101
6                                                                    110
7                                                                    111
8                                                                   1000

Digital data 

We have seen that the PC appears capable of handling data, if it can receive them as 0's and 1's. This data format is called digital. If we can translate our daily data from their analog format to digital format, they will appear as chains of 0's and 1's, then the PC can handle them. So, we must be able to digitize our data. Pour text, sounds, and pictures into a funnel, from where they emerge as 0's and 1's:

Bytes 

The most basic data processing is word processing. Let us use that as an example. When we do word processing, we work at a keyboard similar to a typewriter. There are 101 keys, where we find the entire alphabet A, B, C, etc. We also find the digits from 0 to 9 and all the other characters we need:,.-;():_?!"#*%&etc..
 All these characters must be digitized. They must be expressed in 0's and 1's. Bits are organized in groups of 8. A group of 8 bits is called a byte.

8 bits = 1 byte, that is the system. Then, what can we do with bytes? First, let us see how many different bytes we can construct. A byte is an 8 digit number. We link 0's and 1's in a pattern. How many different ones can we make? Here is one: 01110101, and here is another: 10010101.

We can calculate that you can make 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 different patterns, since each of the 8 bits can have 2 values. 2 8 (two in the power of eight) is 256. Then there are 256 different bytes!●

Now we assign a byte to each letter and other characters. And since we have 256 patterns to choose from, there is plenty of room for all. Here you see some examples of the "translation:"

Character    Bit pattern     Byte number                                    
                                                       
A                  01000001          65                                                    
B                  01000010          66                                                      
C                  01000011          67                                                        
a                   01100001          97                                                      
b                   01100010          98                                                      
o                   01101111         111                                                        
p                   01110000         112                                                        
q                   01110001         113                                                        
r                    01110010        114                                                        
x                   01111000        120                                                        
y                   01111001        121                                                        
z                   01111010        122
‰                10001001        137
   >               00111110        62
©                 10101001         169      
 9                 00111001         57   
2                  00110010         50      
1                  00110001         49      
~                  01111110        126      
  \                 01011100         92      
  ¼               10111100        188    
  $                00100100         36
  .                 00101110         46
 :                  00111010         58

When you write the word "summer", you write 6 letters. If the computer has to process that word, it will be digitized to 6 bytes. In other words, the word summer occupies 6 bytes in the PC RAM, when you type it, and 6 bytes on the hard disk, if you save it.

About text and code 

Now we have seen the PC's user data, which are always digitized. But there are many different kinds of data in the PC. You can differentiate between 2 fundamental types of data:
● Program code, which are data, that allow the PC to function.
● User data, like text, graphics, sound.
The fact is, that the CPU must have instructions to function. An instruction is a string of data, of 0's and 1's. The CPU is designed to recognize these instructions, which arrive together with the user input data to be processed. The program code is thus a collection of instructions, which are executed one by one, when the program runs. Each time you click the mouse, or hit a key on the keyboard, instructions are sent from your software (program) to the CPU, telling it what to do next.

User data are those data, which tells the software how to respond. The letters, illustrations, home pages, etc., which you and I produce, are created with appropriate software.

Files 

Both program code and user data are saved as files on the hard disk. Often, you can recognize the type of file by its suffix. Here are some examples:

Content                      File name
Program code            START.EXE, WIN.COM, HELP.DLL, VMM32.VXD
User data                   LETTER.DOC, HOUSE.BMP. INDEX.HTM

This is written as an introduction to naming files. The file name suffix determines how the PC will handle the file.