Why FIRST and FOLLOW in Compiler Design?

Files; the crucial way of containing all confidential information!

During execution, the computer memory needs several files. In order to access these files and retrieve all the essential information, we need ideal tools.

is when the concept of files access methods in os comes into being! 

Though some systems only provide a single access method for all the files, other systems like IBM make use of multiple access methods while getting access to the multiple files. 

Hence, there are several file access methods that are used in an operating system by the user!

Do you want to know about them in depth?

If yes, this blog post is curated just for you. 

Learn the knits and grits of all file access methods and implement them for your system! 

File access methods - an overview 

IThere are various ways through which the operating system accesses the information in a given file which are called file access methods. File access methods like reading from or writing to files stored in the computer memory, several files are stored. 

When any application is in need of a file, your operating system will search for it in the computer memory to get access to all required files. 

Different file access methods 

As there are different ways that an operating system can better access all the information stored in the required files, you can make use of several file access methods.

These methods are touted as file access methods in the os. Each method comes with its own set of advantages and disadvantages that every user should know.

Without any ado, let’s get started!

Sequential access method 

This is one of the most popular methods to access files in the operating system. It gives the simplest, efficient and most convenient way of accessing files in an operating system. 

As the name suggests, the information access in this method will occur sequentially i.e one record will occur and after that the other records will occur. Both editors and compilers use the access files with the help of this method.

In This method the following operations will be mainly performed:

The read operation: Read next is the operation which will read the next portion of a required file by accessing it in the first place. The read next will advance a file pointer by tracking the input and output operations. The write operation: this is the - write next- operation which will be used to add the new node at the end of your file while moving it towards the new end of a file where the written information will be storedReset or rewind: In reset operation, you will get to read the file and write at the head of the operation. 

Working of this method 

Processing in this method will be carried with the help of two given operations i.e read, write. The read operation has the responsibility of reading the next portion of a file after it successfully reads the record. 

The proceeding pointer may automatically read it to the next given record to track the input or output operations. Writing operation will be responsible to write at the end of every file.

Advantages of this method:

This method is easy to executeIt offers faster access to next method in a structured order 

Disadvantages of this method are:

To perform the read-write operations, this method may take more timeInserting any new kind of record may require some large proportion of a file 

Direct access method 

In a direct access method, files are regarded as the sequence of records and blocks. The method gives you the benefit to access any block in a random order. It is also known as the real time access method as irrespective of the sequence, records can be read anytime. 

The main example related to this method is file access in the database when the query in a corresponding block will be accessed for the instant feedback. This access will save your time where the large data will be present. 

Here the hash function or the index method will help you in performing the read next operation in your block. The read next or the write next operations will be performed with read “n” or write “n”. 

N represents the number of blocks in this case. The more amazing approach in this case would be to use the direct access in order to map all positions for performing the read operations in a particular block. 

Advantages of this approach are:

The files will be accessed by decreasing the access time To access the block, there will be no need to traverse all blocks present in front of you

Indexed access method 

This is another method which we use to access files. This is the advancement of the direct method as in this method the indexes are being used. 

By browsing the index, any particular record is being accessed with uses of pointers or the indexes. 

To understand this concept in-depth, consider the book store where a database will  contain 12 digit ISBN or a given four digit product price. If the disk will carry 2kb of bytes it may result in the single block. The result will carry 128000 records which will then get reduced to the 1000 blocks that will be considered in each part of the index. 

In order to find the best price of your book, binary search would be best Though, the method may sometimes be considered as an ineffective method as in case of any large database, the large files may result in the large index.

Dining philosophers problem in os

Another synchronisation problem that is often asked from the candidates in coding interviews is dining philosophers problem in os which is a crucial concept of operating system. Here, the philosophers are assumed to sit on a dining table with five chopsticks. They can either pick the chopstick or put it down and start thinking. 

Wrapping up 

Learn all about file access methods in os and broaden your knowledge base with this blog post because it’s never a bad idea to learn something new and exciting.