First Fit, Best Fit and Worst Fit Memory Allocation

Best fit Allocation: It is the Contiguous allocation technique in which file is saved on the blocks whose size is same to file size or little more than file size. E.g. if we want to save a 200 Kb file and one block of 250KB is available then it will be saved to this available block.

The advantage of using this technique is best disk utilization but has the disadvantage that it is slow. Every time we want to save a file, we have to find a space whose size is either similar to file size or is slightly more.

Another Problem Associated with this technique is that if we want to extend the file contents than it can’t be implemented.

Contiguous Allocation

It is the Memory allocation technique in which contiguous blocks of this are used to save files. Whenever a file is created its size is calculated and based upon its size contiguous blocks are allocated to it for store. This allocation can be Best Fit, Worst Fit or First Fit.

The Main Advantage of using this technique is that it provides fast file access since whole file is allocated contagious blocks.

The Problem associated with this technique is that every time we have to calculate the file size and then to allocate the contagious

Linked Allocation

It is a disk allocation technique in which files are stored in a linked fashion and scattered way. Directory entry is used that contains pointer to first disk block of file and each block contains pointer to next block.

These Pointers are not made visible to users. Each block has 512 bytes in size out of which 4 bytes are used to store pointer and rest 508 bytes is used by the user.

This Technique has the advantage that there is no external fragmentation and files can be stored anywhere. Another advantage is that there is no need to define the size of file and it can grow as long as free blocks are available.
 

Problems Associated:
1) Files can be accessed in a serial fashion. E.g. to access n^th   block of disk we have to start from beginning until n^th block comes.

2) Another problem is that extra 4 bytes are consumed from each block for the storage of pointers. This problem is resolved by the use of clusters. Cluster is a combination of blocks into multiples. e.g. 5 blocks of disk can be used as single cluster and only one pointer will be required for 5 blocks.

Index Allocation

It is the Disk allocation technique in which each file has its own index block which is an array of disk block addresses. The n^th entry in the index block points to n^th block of file.

Whenever a file is created its index block is initialized, free block is taken from the disk and its entry is made into index table. whenever  file uses a new block its entry is made into index table. Index table consist of the addresses of all disk blocks on which a particular file is written.

The main advantage of using this technique is that it support direct file access. Another advantage is there is no external fragmentation. There is no need to re define the file size.

Problem associated with this technique is that what should be the size of index blocks? If we use one block for per file index and file is too large than it will not be possible to maintain index on single disk block. To overcome this problem linked index scheme is used where index block are linked together to form a large file index.

How to recover hidden folders from Virus Effected Pen Drive

This is a very common problem that arises many times that we plug our Pen Drive to a Laptop or PC and its Contents got hide. It’s a situation of real shock because media may contain very important information or data for the preparation of which you have spent your plenty of Hours. Here is a simple and very quick trick by following which you can easily recover your Data.

Steps Included:

This is a Simple two-step Process:

      1) Copy and Paste below given code to notepad file and save it as unhider.bat file name or with any file name having .bat extension.

@echo off

@echo ***********************************************************

@echo *Application Compiled by allroundexpert.blogspot.com*

@echo ***********************************************************

Difference between HTTP and HTTPS

Parameter	HTTP	HTTPS
Acronym for	Hypertext Transfer Protocol	Hypertext Transfer Protocol Secure
Description	It is the request response based application protocol in client-server model & is designed to work within the framework of Internet Protocol Suit.	It is a Secured version of HTTP to allow secure transactions. E.g. Net banking. It wraps the entire communication within SSL, thus, encryption starts before any data is sent.
Ports Used	This Protocol works on TCP/IP Port No. 80 or 8080	This Protocol Uses TCP/IP Port No.443 for data communication.
Encryption	This Protocol is a stateless protocol and do not uses any encryption method.	HTTPS uses long term public and secret keys to exchange a short term session key to encrypt data flow between client and server.

Difference between IPv4 and IPv6

Characteristics	IPv4	IPv6
Deployed	1981	1999
Address Size	It uses 32 bit addresses	It uses 128 bit addresses.
Address Format	Dotted Decimal Notation: 192.168.1.1	Hexadecimal Notation: FFFE:F200:3204:0B00: 0122:4555:8001:AB00
Prefix Notation	192.168.1.1/24	2FFE:0200:6234::/48
Number of Addresses	232= ~4,294,967,296	2128 = ~340,282,366, 920,938,463,463,374, 607,431,768,211,456
Compatibility	It is less compatible to mobile networks.	It is much compatible to mobile networks.
Uses	It is used in 99% of the networks.	It is used only in remaining 1% of networks.