You can either use a direct access storage device or a sequential access storage device as a storage solution but which will be a better one to use may not be an easy decision to make. It will need making a proper comparison between them.
Knowing the differences between them is therefore most necessary in this matter and this is one article that you can rely on in that particular aspect.
In This Article
KEY TAKEAWAYS
- In a Direct Access Storage Device data can be accessed directly but in a sequential access storage device data is accessed sequentially.
- Direct access takes less time since each block has a unique address of its physical location but in a sequential access storage device everything is in a linear sequence.
- All previous addresses in a sequential access storage device need to be accessed to reach a desired location which results in longer wait times in comparison to the DASDs.
Direct vs Sequential Access Storage Devices – The 5 Differences
1. Storing of Data
In the direct access storage devices, data stored in them are accessed directly with reference to the unique address given to each of the blocks or records in it based on their physical location.
This offers a general environment and counting, waiting or sequential searching to reach the ultimate location.
On the other hand, in sequential access storage devices, the entire memory is structured into small units of data that are also called records.
The access to these units is typically made in a linear sequence in these devices.
2. Accessing Process
The unique address and the discrete location of the data allow instant access directly ignoring the other data that is stored within the device.
On the other hand, in a sequential access storage device the desired storage location which is out of order can only be accessed after accessing, not processing though, all of the preceding addresses.
This is because everything is stored in a sequence.
3. Time Taken
The time taken to access a particular data in the direct access storage device is pretty low or equal for accessing every location because the data can be accessed directly or at random based on the unique address of it.
This means that these particular devices are faster in comparison to the sequential access storage devices.
On the other hand, the sequential storage devices are relatively slow because every location before the desired one needs to be accessed.
This time however may vary according to the location sequence of a particular data.
This means that the time taken to access the 8th data will be lower than the time required accessing the 28th data.
Whatever is the case, the accessing time is comparatively higher than the direct access storage devices.
4. Suitability
The direct access storage devices are suitable for those particular applications that do not need accessing every data that is available and stored in the device.
For example, determining the current balance in the account of a customer of a computerized bank or finding the availability of a seat in a specific flight from the reservation records of a computerized airline ticket booking system.
On the other hand, the sequential access storage devices are suitable for those particular applications which need to access, if not process most, if not all of the data records stored in it one after another.
For example, monthly electricity bills, monthly pay slips, and others.
5. Example
A few good examples of a direct access storage device could be optical disks, magnetic disks, and memory storage devices.
On the other hand, a good example of a sequential access storage device is a magnetic tape.
Which is Better – Direct or Sequential Access Storage Device?
Well, both these storage devices have different applications and functionality and therefore both are useful for varied purposes and reasons.
A sequential access storage device is better than a direct access storage device in the sense that data in these devices are accessed in the same specific order all the time.
On the other hand, direct or random access storage devices are better in the sense that the data in them can be searched and found more easily.
This is because these devices allow using indexing due to the unique address and location of the data.
This means that each item in a direct access storage device is distinct and can be identified individually.
However, in a sequential access storage device all the items stored in it resembles a stream and you will need to move up and down this stream to locate a particular address.
In that sense, sequential access data storage is just like a music tape where a number of songs are recorded.
In order to access a particular song, say the 8th one, you will need to access all seven songs before that.
This is because there is no specific address available in these particular types of storage devices to access a specific item.
Yes, the fast forward feature of the system will save you from the trouble of listening to all those seven songs before you get to listen to your chosen eighth.
On the other hand, a direct access storage device is analogous to a Compact Disc.
Any of the songs stored in it, whether it is the first one or the last one can be accessed easily and directly.
All you have to do is type in the number of the song, which is its distinct address, in the system and the system will access it directly in its discrete location and play the song for you.
There is no need to listen to the other songs stored in it before that particular song you want to listen to.
Therefore, the two specific characteristics of the direct access storage devices can be summarized as under:
- Every storage position consists of a unique address and
- Every address can be accessed in the same amount of time without needing to search through all the other storage positions.
Both these are found lacking in a sequential access storage device.
Every accessing process starts right from the beginning and goes till the end to produce the desired output.
In short, direct access storage devices follow a single process but the sequential access storage devices follow two or more processes in an initial and sequential manner.
So, you will need to make a choice depending on your choice, needs, and the given conditions.
Conclusion
Therefore, coming to the end of the article, now you surely know a bit more than you did before reading this article about the differences between the direct access storage devices and the sequential access storage devices.
This surely will help you to make a more confident and quick choice.