I'm not sure this is the community in which should I ask this question, if it isn't, I'm willing to transfer it.

According to this article:

Track positioning also follows two different methods across disk storage devices. Storage devices focused on holding computer data, e.g., HDDs, FDDs, Iomega zip drives, use concentric tracks to store data. During a sequential read or write operation, after the drive accesses all the sectors in a track it repositions the head(s) to the next track. This will cause a momentary delay in the flow of data between the device and the computer. In contrast, optical audio and video discs use a single spiral track that starts at the inner most point on the disc and flows continuously to the outer edge. When reading or writing data there is no need to stop the flow of data to switch tracks. This is similar to vinyl records except vinyl records started at the outer edge and spiraled in toward the center.

There should be reasons why choosing one strategy over another in each case, Pros and cons. Wich are they?

  • 3
    \$\begingroup\$ I think your article says it pretty clearly. For data devices that are not sequentially read/written, it's easier to track a concentric ring and seek to another ring when necessary. For a real-time sequential device, with minimal buffering, the single spiral track avoids interruptions to the data stream. \$\endgroup\$
    – DoxyLover
    Jan 1 '17 at 23:38
  • \$\begingroup\$ @DoxyLover Ok if that's true, but what part of the article says that? Can you copy it please? The part I myself posted? \$\endgroup\$ Jan 1 '17 at 23:57
  • 1
    \$\begingroup\$ Next to last sentence. \$\endgroup\$ Jan 2 '17 at 0:01
  • \$\begingroup\$ @WhatRoughBeast Ok, then that means spiral is superior in that aspect that concentric. In which aspect is inferior? (Because if there isn't why use concentric?) \$\endgroup\$ Jan 2 '17 at 0:09
  • \$\begingroup\$ DoxyLover explained that: non-sequential access tracking is easier using concentric rings than a spiral. \$\endgroup\$ Jan 2 '17 at 3:03

As the snippet you posted states, spiral is better for continuous audio/video without the need for buffering whereas concentric rings are better for data that isn't necessarily sequential in nature. If you have data like pictures or files or anything else that needs to be read or written in a random manner, then concentric rings would be better because you can have everything indexed at the beginning so that you can jump straight to the ring that contains your specific data.

In summary:
Pros of spiral:

  • No need for buffering.
  • Ideal for continuous streams of data

Pros of concentric:

  • Indexable
  • Random access capability

They both have their advantages and when electronics were more expensive, spiral rings were the better engineering tradeoff. Once you can make a cheap buffer, the advantage of spiral ring media is virtually entirely eliminated because a buffer with a concentric ring technology gives the ability to have random access capability while making streaming data equally ideal to use.

  • \$\begingroup\$ Thank you very much! By the way, here it compares CD and cassetes. It says CD are direct access instead of random access? \$\endgroup\$ Jan 2 '17 at 1:49
  • \$\begingroup\$ @Santropedro The same link you gave says direct and random are virtually exactly the same: "random access (more precisely and more generally called direct access" \$\endgroup\$
    – horta
    Jan 2 '17 at 5:51

One track media like CDs and DVDs were specifically designed for continuous playback of media.

  • Their advantages include:

    1. Data is available to hardware as needed.
    2. Less memory lower hardware cost.
    3. Less synchronization and addressing overhead. (More room for data.)
  • There disadvantages include:

    1. No way to go back and re-read error data.
    2. Really long seek times.
    3. Can not easily go back and write more data.

Concentric tracks like hard disk drives use were designed for error free random data access.

  • Their advantages include:

    1. Fast seek times.
    2. Able to randomly read and write data.
  • Their disadvantages include:

    1. More overhead needed for synchronization and addressing. (Less room for data.)
    2. More hardware needed to access data.

So, from this we see that a 1 track paradigm is better for media while a concentric track paradigm is better for data storage. And since CDs and DVDs are usually created for media, they are made using 1 track. While HDDs are created to store and retrieve data. So HDDs use a concentric tracks.

  • \$\begingroup\$ This doesn't make much sense. All of the issues you raise are specific to the recording technology, and have nothing at all to do with the choice of track layout. \$\endgroup\$
    – Dave Tweed
    Jan 2 '17 at 0:26
  • \$\begingroup\$ So, now I state the pros and cons of 1 track and concentric track paradigms. That is, 1 track is good for media and concentric tracks are good for data. And then, because CDs and DVDs are usually used for media, say that is why they are 1 track. While HDDs are used for data, and that is why HDDs use concentric tracks. \$\endgroup\$
    – st2000
    Jan 2 '17 at 3:08

CD and DVD were designed for media recording - constant data rate, with relatively few random seeks (which cause high seek times, usually hundreds of ms). As a result, a standard CD player have constant linear velocity, and the tracks are arranged in a spiral. Adjusting the read head (Laser) location is relatively easy, just follow the track. You have to remember that the CD first appeared in 1982, the electronics were quite primitive at the time.

HDs allow for more random access patterns, spin at a constant speed (5400, 7200 and even 15000rpm) with relatively low seek time (few ms), so adjusting the head location is more complicated when random seeks are thrown into the mix.


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