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Old 07-16-2003, 03:03 PM   #1
jon_k
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/dev/null


What is /dev/null and /dev/zero

They are a device of course and if a file or any type of output is put there it gets put in a black hole which crushes it into nothingness.

But what is it exactly?

hda is a virtual item that resembles the Hard Drive
cpu simulates your cpu
ram0-19 simulates your ram sticks

but what does null and zero simulate? is there an actual chip on your machine for "null" and "zero"

Another question is why is there two devices if they both do the same thing?

Did someone originally create zero but then someone else thought null was better so they made a symbolic link or something??

Thanks, regards,
JOn K
 
Old 07-16-2003, 03:13 PM   #2
Proud
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Null is neither 0 nor 1, it is a non-existent state in binary, it is the lack of a value.
 
Old 07-16-2003, 03:25 PM   #3
jon_k
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RE:

So is there a chip that does that or is that performed by the cpu of changing a value to null or "nil"
 
Old 07-16-2003, 03:32 PM   #4
Proud
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A value cannot be null, it's when the program/processor doesnt have a value assigned to that variable/memory address.
Basic electronics classes taught me that when memory addresses are not connected to the data bus, they're disconnected so that another address can be connected and put it's contained value of 0 or 1 on the bus. When not connected those addresses would have an unknown value.
In binary 0 is not nothing, null is

Deleted data is often overwritten with 0s though, unless the filesystem is one which just reports the disk space to be free to be written to, and not containing anything atm.

Hope this helps a bit.

Last edited by Proud; 07-16-2003 at 03:33 PM.
 
Old 07-16-2003, 03:39 PM   #5
tcaptain
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I don't think /dev/null is supposed to refer to an actual device...

BUT I also would be interested in how it came to be...I mean you don't really have something like that in windows (that I know about anyway)...its useful for routing output into nothing...but how did we come to have it?
 
Old 07-16-2003, 03:40 PM   #6
fancypiper
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If you use something like "if=/dev/zero", the input file (/dev/zero) acts like a drive (device) full of zeros so you can copy it to another device such as an actual drive (of=/dev/hda)

So, to fill your entire drive with zeros (a good idea if some virus infected os was installed), you have

dd if=/dev/zero of=/dev/hda

Result, a clean drive needing a low level format.
 
  


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