Kernal in Brief

What About Kernal ??

Kernal Is The Important Part in any OS. used To Manage All resources of computer like I/O , Virtual Memory , Disk Management and More .

When We Speak As Layers Kernal is second layer before CPU, Memory , Devices Then Kernal Finally Application With Gui Or Not that isn’t the point :).

From Here About Types Of Operating systems
http://7shad01.blogspot.com/2012/09/operating-systems-types.html

Some Special Systems don’t Need Kernal But All multitasking and multiple users
Most in need to kernal as principle part of its parts 

in order to manage processes , tasks , users , time and usage in general for all users or management tasks in multitasks os .

this important part need design in order to work correctly with no errors

there are 3 models of designs : Monolithic kernels


In this model os merged in one part kernal not separated this make os faster but any error make all system fails like virus or malware in general .Microkernels Kernals


not as one this divides os into parts but time for sending and receiving data is wasted . any part is standalone .
Hybrid kernels


merged design from Microkernels and Monolithicto make system faster and working with high performance .

That as i can say a definition about kernal


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Dr.7shad

Interesting Reverse Engineering :)

What is reverse engineering?

Reverse engineering is the process of taking a compiled binary and attempting to recreate (or simply understand) the original way the program works. A programmer initially writes a program, usually in a high-level language such as C++ or Visual Basic (or God forbid, Delphi). Because the computer does not inherently speak these languages, the code that the programmer wrote is assembled into a more machine specific format, one to which a computer does speak. This code is called, originally enough, machine language. This code is not very human friendly,  and often times requires a great deal of brain power to figure out exactly what the programmer had in mind.

What is reverse engineering used for?

Reverse engineering can be applied to many areas of computer science, but here are a couple of generic categories;

• Making it possible to interface to legacy code (where you do not have the original code source).
• Breaking copy protection (ie. Impress your friends and save some $$).
• Studying virii and malware.
• Evaluating software quality and robustness.
• Adding functionality to existing software.

The first category is reverse engineering code to interface with existing binaries when the source code is not available. I will not be discussing this much, as it is boring.

The second category (and the biggest) is breaking copy protection. This means disabling time trials, defeating registration, and basically everything else to get commercial software for free. This we will be discussing at great length.

The third category is studying virus and malware code. Reverse engineering is required because not a lot of virus coders out there don’t send instructions on how they wrote the code, what it is supposed to accomplish, and how it will accomplish this (unless they are really dumb). This is a pretty exciting field, but requires a great deal of knowledge. We will not discuss this much until later on.

The fourth category is evaluating software security and vulnerabilities. When creating large (think Windows Operating Systems), reverse engineering is used to make sure that the system does not contain any major vulnerabilities, security flaws, and frankly, to make it as hard as possible to allow crackers to crack the software.

The final category is adding functionality to existing software. Personally, I think this is one of the most fun. Don’t like the graphics used in your web design software? Change them. Want to add a menu item to encrypt your documents in your favorite word processor? Add it. Want to annoy your co-workers to no end by adding derogatory message boxes to Windows calculator? Let’s do it. This we will be getting into later in the series.

What knowledge is required?

As you can probably guess, a great deal of knowledge is necessary to be an effective reverse engineer. Fortunately, a great deal of knowledge is not necessary to ‘begin’ reverse engineering, and that’s where I hope to come in. That being said, to have fun with reversing and to get something out of these tutorials you should at least have a basic understanding of how program flow works (for example, you should know what a basic if…then statement does, what an array is, and have at least seen a hello world program). Secondly, becoming familiar with Assembly Language is highly suggested; You can get thru the tutorials without it, but at some point you will want to become a guru at ASM to really know what you are doing. In addition, a lot of your time will be devoted to learning how to use tools. These tools are invaluable to a reverse engineer, but also require learning each tool’s shortcuts, flaws and idiosyncrasies. Finally, reverse engineering requires a significant amount of experimentation; playing with different packers/protectors/encryption schemes, learning about programs originally written in different programming languages (even Delphi), deciphering anti-reverse engineering tricks…the list goes on and on. At the end of this tutorial I have added a ‘further reading’ section with some suggested sources. If you really want to get good at reversing, I highly suggest you do some further reading.

MBR and GPT Disks

What is the different between MBR and GPT Disks ??

MBR is the standard partitioning scheme that's been used on hard disks since the PC first came out. It supports 4 primary partitions per hard drive, and a maximum partition size of 2TB.

GPT disks are new, and are readable only by Windows Server 2003 SP1, Windows Vista (all ersions), and Windows XP x64 Edition. The GPT disk itself can support a volume up to 2^64 blocks in length. (For 512-byte blocks, this is 9.44 ZB - zettabytes. 1 ZB is 1 billion terabytes). 

It can also support theoretically unlimited partitions.Windows restricts these limits further to 256 TB for a single partition (NTFS limit), and128 partitions.Only Itanium systems running Windows Server 2003 and Windows Vista systems with an EFI BIOS can boot from a GPT disk. The other operating systems mentioned earlier can use GPT disks as data disks but not boot disks.

Operating Systems Types

                         بسم الله الرحمن الرحيم 

                                    

                 Operating Systems Types 

• Real-time operating system (RTOS) - Real-time operating systems are used to control machinery, scientific instruments and industrial systems. An RTOS typically has very little user-interface capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use. A very important part of an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time, every time it occurs. In a complex machine, having a part move more quickly just because system resources are available may be just as catastrophic as having it not move at all because the system is busy.
• Single-user, single task - As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld computers is a good example of a modern single-user, single-task operating system.
• Single-user, multi-tasking - This is the type of operating system most people use on their desktop and laptop computers today. Microsoft's Windows and Apple's MacOS platforms are both examples of operating systems that will let a single user have several programs in operation at the same time. For example, it's entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the Internet while printing the text of an e-mail message.
• Multi-user - A multi-user operating system allows many different users to take advantage of the computer's resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.

It's important to differentiate between multi-user operating systems and single-user operating systems that support networking. Windows 2000 and Novell Netware can each support hundreds or thousands of networked users, but the operating systems themselves aren't true multi-user operating systems. The system administrator is the only "user" for Windows 2000 or Netware. The network support and all of the remote user logins the network enables are, in the overall plan of the operating system, a program being run by the administrative user.

With the different types of operating systems in mind, it's time to look at the basic functions provided by an operating system.