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View Full Version : Rewrite again to CD-R works



E.ric
04-09-2002, 11:48 PM
Now I was on the understanding that one could write to a CR-RW as many times
as you like (at least 1000), and to a CD-R only once, But tonight I run
"HTML Tidy" on my HTML file I wrote and it deleted part of the information,
before I noticed the missing data , I burnt the file to a CD-R. But I was
able to save the same file again and get back the missing data,

So now I take it, when you write the same file name to a CD-R again, the
writer destroys that part of the CD that holds that file and puts the
updated file in some other empty space on the CD.

helvista
05-09-2002, 12:30 AM
Wooo ... I'm gonna try that one now :). Stay tuned.

SoniKalien
05-09-2002, 12:43 AM
Lemme get this right.

You had file X.

You burned file X to CD-R.

You took something away from file X.

You burned file X to same CD-R

You took file X off CD-R to find original file intact.

Does it not follow that the modified version never got burned at all?

godfather
05-09-2002, 12:58 AM
Also the "old" file does not get "destroyed"
The TOC just doesnt point to it anymore, but its on there...(BTW its a whole new TOC as well)

helvista
05-09-2002, 01:34 AM
Well, that was an interesting lil experiment. I did as you suggested and it worked. I placed an unused CD-R (DataLife, 700MB) into my CD burner. I copied a directory onto the blank CD-R and checked the content of the CD to make sure that it copied correctly. I then added a text file to the same directory on my hard drive and copied the updated directory to the same CD-R. As you suggested it wrote to the CD-R, no complaints. I checked the contents of the CD and it had updated the directory correctly (it had the new text file I added).

But then I decided to copy over a new directory ... different name, size and location to the same CD-R. Now this is what amazed me ... it wrote to the CD-R without any complaints. I checked the CD's content and it displayed the old directory. I ejected the CD and closed the CD drive door (whatever its called), with the same CD-R in it, and checked the contents again. The old directory was gone and the new directory I copied over was now displayed .. it seems it had copied the directory over correctly. I just had to open & close the CD drive door for the contents to be displayed correctly.

I thought maybe this was a unique characteristic of DataLife CD-R so I repeated the above process but this time with an already used Elite DATA 700 MB CD-R. Nero did complain and asked me if I wanted to finalise the CD. When I cancelled Nero proceeded to write to the CD-R. As before I had to open and close the CD drive door in order for the new contents to be displayed.

I am absolutely baffled as to why this is since I was told & read that one can only write to a CD-R only once. If I had not read your post I would not have even thought of testing it out to determine the validity of what I was told ... I feel like such a monkey, monkey see monkey do.

Good spotting!

E.ric
05-09-2002, 07:01 AM
> Lemme get this right.
> You had file X.
> You burned file X to CD-R.
> You took something away from file X.
> You burned file X to same CD-R
> You took file X off CD-R to find original file
> intact.
> Does it not follow that the modified version never
> got burned at all?

No no no no
I saved a file to CD-R, then I found, #$%^ it saved OK but not what I hoped to save, So I fixed the error on my hard drive copy and saved it again, and :) just how I liked it.

NathanTheKind
05-09-2002, 09:49 AM
Correct. it is possible to right to a CDR more than once. My Uncle copies photos to his CDs and then finds more and adds them as well. This can sometimes be a task to do, but once you know how to do it it is easy. If you are wondering how to do this though you will have to figure it out yourself. I am useless at explainning things and this is quite a complicated thing to do. At least I found it was.

:)

Billy T
05-09-2002, 10:48 AM
Hi there

When you completed all your tests, did the remaining space on the CD show that the sum of all writes had been used, or just the size of the last file/directory written?

For example, if you wrote a 250MB file then modified the original by changing say a 50MB file and rewrote it, would the CD then show 300MB used and 350MB free (assuming it had 650MB to start with) or would it still show 250MB used and 400MB free. If the former then a new TOC is probably being written pointing to the new entry, and if the latter, you would be rewriting the original file space which I always understood to be write-once only as an absolute, hence the piles of coasters people accumulate.

I hasten to add that I am theorising here as I do not have a CD writer myself, however the concept intrigued me. Assuming that a CD-R cannot be rewritten over an area that had been burned (and I'd be very surprised if it could) an absolute "write once" constraint would suggest that the TOC can't be modified or a new one written, while E.Ric's experience would seem to suggest that a new TOC can be written with the location of the modified file recorded along with the locations for the original files. The old TOC would become inaccessible.

But then, I could be wrong. :8}

Cheers

Billy 8-{) ?:|

antmannz
05-09-2002, 01:44 PM
Hmmm .... interesting ......

I think this is what is probably happening:

Session 1:
Files 2meg.txt, 200meg.bmp, 10meg.gif, & 35meg.jpg get written to the root folder of a blank cdr. Session TOC written and closed.
Total file size = 2 + 200 + 10 + 35 = 247Mb.
Total space used = 247Mb.
Total space remaining = 650 - 247 = 403meg.

CD stays in tray, 2meg.txt is altered in size to 50meg
Session 2:
Files 2meg.txt (now 50Mb), 200meg.bmp, 10meg.gif, & 35meg.jpg get written to the root folder of the existing cdr. Session TOC written and closed.
Total file size = 50 + 200 + 10 + 35 = 295Mb.
Total space used = 247 + 295 = 542Mb.
Total space remaining = 650 - 542 = 108Mb.

CD stays in tray.
Attempt to access 2meg.txt, you get the copy from session 1 because session 1's TOC is cached by Windows so it will point to the earlier portion of the cd, but take the cd out of the tray and reinsert it and you will get the larger copy of 2meg.txt because the TOC has been flushed from Window's cache, and you are accessing the TOC physically from the CD.

Peter H
05-09-2002, 01:52 PM
If you don't finalize the cd-r, of course you can add more, until the disc is full. Or am I missing something.
Bye

Lohsing
05-09-2002, 02:19 PM
Peter H is right... Nero has a "start multi-session cd" option for writing... here you can set different options for writing your cd's... among these options, you are able to do what you have described... what it actually does is write the new text file to the folder you have created on the CD... a new TOC is then created which does not refer to the old text file which is physically still on the CD.

So... you HAVE written to the cd-r more than once, but you haven't actually written over the information on the cd-r as you would do on a cd-rw.

Hope this helps.

Lo.

helvista
05-09-2002, 04:18 PM
There were apparent flaws in that lil experiment I did in the wee hours of the morning. Decided this after reading Billy, antmanz and Lohsing's post so I decided to do it again, but this time including values.

Starting point:
------------------
DataLink 700MB CD-R (blank)

1st run:
----------
size of file on h/d = 15.052 MB
stats of CD-R after writting file:

used space: 15,423,488 bytes 14.7 MB
free space: 0 bytes 0 bytes
capacity: 15,423,488 bytes 14.7 MB

2nd run (same CD-R):
---------------------------
using different file, size on h/d = 28.432 MB
stats of CD-R after writting file:

used space: 28,803,072 bytes 27.4 MB
free space: 0 bytes 0 bytes
capacity: 28,803,072 bytes 27.4 MB

3rd run (same CD-R):
--------------------------
using different file, size on h/d = 642.6MB
stats of CD-R after writting file:

used space: 642,971,648 bytes 613 MB
free space: 0 bytes 0 bytes
capacity: 642,971,648 bytes 613 MB

*note: nero now complain and asked if I wanted to finalise the CD-R. I clicked on no. nero then proceeded to write to the CD-R.

4th run (same CD-R):
--------------------------
using different file, size on h/d = 1,091 bytes

*note: would not write
-> medium required for the compliation: CD-R/RW
-> medium type in the recorder: [empty]

5th run (same CD-R):
--------------------------
using different file, size on h/d = 1 kb

*note: the same result as the 4th run.


CONCLUSION:
------------------
It seems when the CD-R is being rewritten too it doesn't delete the previous file but rather the TOC doesn't point to it anymore. Even though the size reported now matches the new size of the file copied over the amount of used space is the [old size of the file + the new size of the file]: even though there is no direct evidence of this when viewing the stats. It will get to a stage when no more writting to the same CD-R is possible as suggested during my 4th and 5th run.

But of course I'm merely repeating what had already been suggested by billy, antmanz and Lohsing. It is nice to prove to oneself though.

Couple of good points came out of this though. 1: never do experiments in the lil wee hours of the morning. 2: I always assumed if the CD-R is written too, regardless of the free space left, it can not be written to again.

Well anyway... that was fun, next!

E.ric
06-09-2002, 12:49 AM
Good to see the maths but..
Saved some files tonight had "Total size" of files came to 28.7 meg

Added a few lines of text to a HTML saved it, now the file is 13 K in size saved to CDROM again, now 96 Meg "Total size" used on CDROM.