What is Sequential access? What is Random access?

 What is sequential and random   access.

What is sequential access 

• A sequential access memory device reads data from the board. In other words, information on a serial device can only be retrieved in the order in which it was stored. Data is stored on a storage medium one after the other in a predetermined order (for example, in numerical order). Sequential processing is particularly suitable for applications such as monthly payroll or monthly electronic invoices that require access to each address. If you are working with a sequential-access device, if the information is stored at the last address, the data stored at the last address cannot be accessed until all previous locations in the sequence have been scanned. In other words, in order to find an individual data item, the data stored on the tape must be searched until the desired item is found. 

• Sequential-access memory, such as magnetic tape, is organized by arranging memory cells in a linear order. There is no specific storage address that these cells can directly address. Instead, data is presented sequentially for writing and retrieved sequentially for reading.

What is random access 

• In the case of random access devices, information is available randomly, that is, the location of any memory system in the device can be selected randomly. Thus, any location in the device can be accessed almost simultaneously in any order. In other words, each storage location (1) has a unique address and (2) can be accessed individually at approximately the same time without searching for other storage locations. Magnetic disks and CD-ROMs are typical random access storage devices. Any data record stored on a magnetic or optical disk can be accessed directly for approximately the same period of time. Figure below shows random access storage versus continuity:-

Data is processed in a computer system by electronic or magnetic signals (i.e. RAM) or not on a medium. and stored (i.e. magnetic disk). This is called a "two-level" or binary representation of data. Transistors and other semiconductor circuits exist in either conductive or nonconductive states. For magnetic media such as magnetic disks or tapes, these two states are represented by magnetic dots whose magnetic fields have one of two different directions or poles. 

For any electronic circuit, the conductive (on) state represents the number 1, while the nonconductive (off) state represents the number 0. This is only a positive argument. There can always be a countertradition, which we call a negative argument. For a magnetic medium, the magnetic field of a magnetic dot in one direction represents 1, and the magnetization in another direction represents 0.

The smallest piece of data is called a bit, which can have the value 0 or 1. The capacity of a memory chip is usually expressed in terms of bits. A group of 8 bits, called a byte, represents a data character in most computer coding schemes. Thus, the capacity of a computer's memory and secondary storage devices is usually expressed in terms of bytes. Computer codes such as ASCII (American Standard Code for Information Interchange) use various arrangements of bits to create bytes representing the numbers 0 through 9, letters of the alphabet, and so on.