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Re: Image Disk Size
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Re: Image Disk Size


  • Subject: Re: Image Disk Size
  • From: Luther Fuller <email@hidden>
  • Date: Wed, 14 May 2008 15:49:11 -0500

On May 1, 2008, I wrote:
I have an AppleScript, which creates sparseimage files of various capacities.

In Tiger, when I selected "4.7 GB" (decimal), I got a sparseimage file with capacity of 4.38 GB (binary) which was the exact, perfect size to burn a DVD.

In Leopard, the same selection now produces a sparseimage file with capacity of 4.06 GB. (I don't know if that's binary or decimal.) I haven't yet tried to burn a DVD with one of these files.

Has something changed that invalidates my calculations in the script? If so, what?

I've finally had time to look into this ... and I've answered my question ... and have another.


My original code in Tiger was ...
do shell script "hdiutil create -type SPARSE -megabytes " & imageSize & ¬
" -fs HFS+ " & imagePath & " -volname " & quoted form of imageName & " -attach"


I did not have a -layout specifier in the command. On a PPC machine the default layout is SPUD and on an Intel machine the default is GTSPUD. That accounts for the size difference. So , I added " -layout NONE " to my command and now the size of a 4.7 GB(decimal) sparseimage is 4.38 GB(binary), which is correct.

If you use Disk Utility to make a sparseimage file, you will have to choose Partitions: where one of the choices is "No partition map". This is equivalent to " -layout NONE ".

New question ... Is " -layout NONE " a safe choice of Partitions? All I'm doing is burning data to an optical disk. Is there any good reason to use one of the other partition types? (such as SPUD or GPTSPUD)

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 >Image Disk Size (From: Luther Fuller <email@hidden>)

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