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Posted: Mon Jul 02, 2012 6:46 pm Post subject: Re: What is a bit level image and how is that different from
nicks_sarang wrote:
Differentiate between Bit level image & an ISO?
It would help if you told us what you are after
An ISO file *is* a bit-level image -- as long as you select the appropriate system level -- in that case ISO-9660. If you don't, you have to tell what system level is relevant.
this is the actual question i came across "What is a bit level image and how is that different from an ISO? "
can u tell me whats the answer for this question??
Presuming you are talking about an ISO 9660 file system format image file (usually .iso), and a "bit-level" image of a hard disk drive (.dd or .001) - they are not the same thing.
A bit-level image can be made of any electronic media, including a CD and DVD. It will not necessarily produce an ISO 9660 file system image (ISO image).
On the other hand, not all ISO image creation from media is identical to the actual media. This is because the media may contain leading, intermediate and end sections or "gaps" which in normal ISO format do not require to be duplicated.
Posted: Thu Jul 12, 2012 10:03 am Post subject: Re: What is a bit level image and how is that different from
athulin wrote:
nicks_sarang wrote:
Differentiate between Bit level image & an ISO?
It would help if you told us what you are after
An ISO file *is* a bit-level image -- as long as you select the appropriate system level -- in that case ISO-9660. If you don't, you have to tell what system level is relevant.
A CD-ROM can have an ISO-9660 file system present, a Joliet file system present, or both file systems present on different parts of the disk (much like different partitions on an HDD). As a result, selecting ISO-9660 would only get some of the data. For a true bit-perfect copy, you need something to RAW read the drive, getting ever bit from the disk and not attempting to perform any interpretation of the data. This also means NO ERROR CHECKS. The CRCs on the CD-ROM disk must be copied as is, and the data must NOT be compared with the CRCs, as this will void data that doesn't have the right CRC. Every bit from the CD-ROM disk must be copied "as is", and saved to a file called the disk image. Only ONE piece of software can do that as far as I can tell. It's called Blind Write. You can buy it at http :// www . blindwrite . com/
While advertised as an illegal game copying tool (because it ignores the bad CRCs that are put in place by the game company as copy protection that stops MOST software from reading the protected files or even copying them into an ISO), it also is useful for forensically perfect disk images of a suspect's CDs and DVDs (and for the same reason, it ignores all formatting and error correction CRC routines).
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