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Capacity of SSD

T

thebigf80

macrumors newbie
Original poster
Nov 19, 2020
13
7
Austria
I received my new MacBook Air M1 8C/8GB/512GB today. I replaces my old 2011 MacBook Pro 15.

My first impressions are very good, seems I made the right decision.

But there is one thing that irritates me:
The SSD is shown as a 500GB Flash Drive (494GB available for volume, as about 6GB are reserved by the recovery partition, 398Gb free right now). Harddisk utility states the model as APPLE SSD AP0512Q Media with a capacity of 500.277.792.768 bytes (=500,28GB in the decimal system).

As I'm working in the IT for long, I'm aware of decimal and binary calc (Big Sur is showing decimal as the drive manufacture) which does not explain the missing 12GB here... so it is not a 512GB drive as Apple claims.

Is this the same for other owners? Which SSD/capacity do you have in your 512GB Air/Pro M1 models?
 
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What does it say when you view it in Disk Utility? My 512GB SSD in my old MBP shows as 512GB.
 
Bildschirmfoto 2020-11-19 um 21.49.29.png

That's a screenshot of the disk utility.. as I wrote above 500,28GB
 
thebigf80 said:
As I'm working in the IT for long, I'm aware of decimal and binary calc (Big Sur is showing decimal as the drive manufacture) which does not explain the missing 12GB here... so it is not a 512GB drive as Apple claims.

Is this the same for other owners? Which SSD/capacity do you have in your 512GB Air/Pro M1 models?
Click to expand...

Since Catalina, macOS splits the drive into two volumes. Your normal data volume plus a semi-hidden System volumes of approximately.... you guessed it... 12GB.

Open up Disk Utility and you'll see this more clearly.

www.idownloadblog.com

Why does the macOS Catalina installer create a hidden Data volume on your Mac?

macOS Catalina's installer splits your Mac into Data and System folders, to help enhance data security. Understand why in this iDB explainer.
www.idownloadblog.com www.idownloadblog.com
 
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On my 16" MacBook Pro, 1 TB is listed as "1,000,555,581,440 bytes" - "1 TB" in the main Disk Utility interface.

On my M1 Mac Mini, 256 GB is listed as "251,000,193,024 bytes" - "251 GB" in the main Disk Utility interface.

But on the tech specs page, it does say "actual formatted capacity less."
 
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Anonymous Freak said:
On my 16" MacBook Pro, 1 TB is listed as "1,000,555,581,440 bytes" - "1 TB" in the main Disk Utility interface.

On my M1 Mac Mini, 256 GB is listed as "251,000,193,024 bytes" - "251 GB" in the main Disk Utility interface.

But on the tech specs page, it does say "actual formatted capacity less."
Click to expand...
Overprovisioning is common with SSDs to extend the usable life.
 
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I already posted a shot of the disc utility and the physical drive above.

Physical drive of 500,28GB is split into three partitions:

MacintoshHD - 494,38GB
disk0s1 - 524,3 MB (guess it's boot)
disk0s3 - 5,37GB (guess it's hidden recovery)

Where should I see a hidden 12GB volume? Sorry,... I do not see it:

Bildschirmfoto 2020-11-19 um 22.04.45.png
 
Reserved spare cells in page pool. Reserved hardware. A special recovery diagnostic tbat really is reserved?
 
I'm seeing the same thing on my MacBook Air. So these are actually 489GB drives. Annoying for sure, but not completely unexpected.

Whatever drive cabal created this fake "GB" rating that has nothing to do with actual gigabytes are absolutely evil. But it seems to be something we have to live with at this point.
 
thebigf80 said:
Where should I see a hidden 12GB volume? Sorry,... I do not see it:
Click to expand...

There's a Mini teardown video where the person calls out the sizes printed on the two SSD chips: "128GB and 160GB." I presume this was a 256GB Mini. So why is it provisioned to 9/8ths the advertised size? An SSD needs massive amounts of extra bytes per sector for error correction. Also for overprovisioning of sectors in case of failed sectors. Finally, there's overhead to keep track of the logical to physical sector mapping.
 
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