Disc access

I was reading through my architecture textbook, and it says:

So it seems to me that a couple of things would make a good system for disc interaction:
- Placing files closer to the centre of each platter the smaller the files are.
- Forcing the drive to write contiguously whenever possible.

Can anyone give me more notes or ideas on this please? Ideas on arranging data on the disc, that is.

 

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It's also dependent on how many heads your reading with.
For instance:

I had a 1x speed CD-rom (yeah I know... some call it old, but I remember using tape) This meant as you can guess that it lacked a large number of heads (which I believe means how many tracks can be scanned together)

One day I placed a magazine disk to load Delphi and it wouldn't load it because it kept jumping back and forth until it made the CD skip. The problem was the installation had been cut to the disk but it wasn't configured for running on a CD-rom especially lacking heads (in comparison to a harddrive).

If the files were sequenced properly then it would only need to load file after file in sequence.

 

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The real problem is that files are not the same size! A lot of the small files are deleted and new ones made. This leads to a lot of writing 6k- 9k files in 10k holes. Leaving not enough gap to be useful.

If you are filling in the 10k hole. and then the program decides to keep on going for another 5k. Do you :-

A - move the whole file to a new 15 k hole ?
B grap another 5K hole ?
C move the file in the way to somewhere else ?
D something else ?

Of course then the program will decide to write another 50k...

The best we have at the mo is to run a defrag every night that re-arranges the files into continous areas (until the next add) and removes the gaps between the files. (The later gives lots of contiguous space for new files to be created).

In short if nothing is changing then you can work out a good layout for reading. But the best layout for writing (adding much more than updating) and retaining a good layout for subsequent reading requires a clarevoiant to plan what is going to happen. Good Luck!

 

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