SSD size not a true 512GB only 500GB!

[joevt]

The SI unit for 1024 bytes is 1 kiB, but usually when people write kB/KB/kb, they mean 1024 bytes.

Right. Except b is usually a bit (e.g. 230.4 kb/s is the max bit rate of an old Mac serial port). Bandwidth (bits per second) is usually measured in decimal.

RAM capacity is still measured using binary because computer science (each address line multiples the capacity by 2).

Apple switched away from using binary for storage devices a long time ago. They were using spinning disks at the time. Disk block size is binary but most everything else wasn't (tracks, cylinders, heads, etc).

 

[Basic75]

The reason you don't see 512 GB (476.84 GiB) or 512 GiB (549.76 GB) is probably because of SSD overprovisioning? For an SSD, the likely size is 512 GiB (a power of 2) like RAM would use. Is some of the size of the SSD taken by ECC?

No, just like on HDDs the space an SSD reserves as spare and uses for error correction is not visible.

 

[Basic75]

Human version of 1000 is equivalent to a computer's 1024, thus 1000/1024 = 0.9765625 conversion rate.

512 GB x 0.9765625 = 500 GB to humans

Hope that helps.

Your calculation is not correct, your factor is for KB, not for GB.

One marketing GB is 1000 * 1000 * 1000, one real GB is 1024 * 1024 * 1024, so you need to apply the third power of your "conversion rate"!

512GB * ( 1000/1024 )^3 = 477GB

 

[Basic75]

Disk block size is binary but most everything else wasn't (tracks, cylinders, heads, etc).

To be fair, for tracks, cylinders and heads there is no natural reason to use powers of two. I mean, you have at most like a dozen heads, and tracks and cylinders are simply what fit. They also were usually given as complete number, not abbreviated.

 

[chama98]

Oh well. It is what it is. I still like my Mac mini.

 

[AlixSPQR]

How surprising Apple uses the highest figures marketing wise.

 

[winxmac]

How storage capacity is measured on Apple devices

Some apps and operating systems, such as iOS 10 and earlier and OS X Leopard and earlier, report storage capacity using the binary system.

macOS and Linux distributions use decimal [base 10] while Windows use binary [base 2]

10^3 = 1000
2^10 = 1024

KiB = kibibyte [base 2]
KB = kilobyte [base 10]

Windows uses KB when it actually means KiB

 

[TechnoMonk]

This is like kids realizing for first time Santa isn’t real.

 

[Wando64]

Why Does My HDD Appear Smaller Than The Advertised Capacity?

www.data-medics.com

 

[Mr.Fox]

I was looking at my Mac mini spec wise in the system report and I discovered this! a 500GB SSD instead of the 512GB advertised and bought. Anyone else had this?

I know it's probably nothing. But I feel robbed of 12GB! lol.

Outrageous! Cheated, stolen, underpaid 12 GB of memory! Execute on the spot! Demand a discount on the missing memory! Do not read the label of the juice, there instead of the promised liter will be 900 ml )))).

 

[theluggage]

I was looking at my Mac mini spec wise in the system report and I discovered this! a 500GB SSD instead of the 512GB advertised and bought. Anyone else had this?

The *big* discrepancy between 512GB and the 494GB or whatever you actually see on "Macintosh HD" is that - as @EugW said - there is a hidden ~5.4 GB recovery partition which lets you boot so you can re-install MacOS over the network. Not sure about the 512GB advertised vs. the 500.28 GB that its showing for the drive. My 1TB studio just shows 1TB (i.e. 1000 GB).

If you option-click on the Apple menu, choose "System Information" and then select "NVMExpress" and then "Apple SSD Controller" you should get the actual number of bytes on the SSD. I get "1 TB (1,000,555,581,440 bytes)" - a figure that I am at a loss to explain in terms of powers of two or 10 but it's quite possible that the SSD has some over-provisioning or allowance for dead cells.

"Over-provisioning" means leaving some of the SSD unformatted so the SSD can never get physically 100% full: SSDs can't actually function without some spare blocks to move data around - roughly speaking, in order to change existing data they have to copy a large block of data to a blank block along with the changes, then wipe the original. If an SSD ever got 100% full, you'd no longer be able to change anything on it without erasing and losing large blocks of data. So, when you manually partition a SSD you might leave, say, 5% unallocated to avoid this - but many SSD controllers have this margin baked in (or set via firmware).

 

[chama98]

The *big* discrepancy between 512GB and the 494GB or whatever you actually see on "Macintosh HD" is that - as @EugW said - there is a hidden ~5.4 GB recovery partition which lets you boot so you can re-install MacOS over the network. Not sure about the 512GB advertised vs. the 500.28 GB that its showing for the drive. My 1TB studio just shows 1TB (i.e. 1000 GB).

If you option-click on the Apple menu, choose "System Information" and then select "NVMExpress" and then "Apple SSD Controller" you should get the actual number of bytes on the SSD. I get "1 TB (1,000,555,581,440 bytes)" - a figure that I am at a loss to explain in terms of powers of two or 10 but it's quite possible that the SSD has some over-provisioning or allowance for dead cells.

"Over-provisioning" means leaving some of the SSD unformatted so the SSD can never get physically 100% full: SSDs can't actually function without some spare blocks to move data around - roughly speaking, in order to change existing data they have to copy a large block of data to a blank block along with the changes, then wipe the original. If an SSD ever got 100% full, you'd no longer be able to change anything on it without erasing and losing large blocks of data. So, when you manually partition a SSD you might leave, say, 5% unallocated to avoid this - but many SSD controllers have this margin baked in (or set via firmware).

Is this what you mean?

 

[theluggage]

Is this what you mean?

Yeah, so it is interesting that - even before the restore partition and other formatting losses - 500,000,000,000 plus change is still sold as 512GB but 1,000,000,000,000 is just described as 1TB... Maybe they just round up the figures differently...

 

[chama98]

Yeah, so it is interesting that - even before the restore partition and other formatting losses - 500,000,000,000 plus change is still sold as 512GB but 1,000,000,000,000 is just described as 1TB... Maybe they just round up the figures differently...

i thought so.

 

[CraigJDuffy]

Feel free to use maths to prove that. 😆

 

[theluggage]

View attachment 2451013

Fine, but that doesn't explain how 512 Gigabytes in an ad turns into 500GB + change.

 

[CraigJDuffy]

Fine, but that doesn't explain how 512 Gigabytes in an ad turns into 500GB + change.

It’s probably the recovery partition and file system overheads - 512GB should only be 477!

 

[theluggage]

It’s probably the recovery partition and file system overheads - 512GB should only be 477!

Recovery partition and file system overheads get you down from 500GB/1TB reported for the device to the 494GB/994GB you get on the "Macintosh HD" partition.

 

[joevt]

diskutil list will list all partitions. There are no hidden partitions.
diskutil info -all will get all the info for all the disks and partitions. It will list sizes in GB and bytes and disk blocks.

 

[dmr727]

Fine, but that doesn't explain how 512 Gigabytes in an ad turns into 500GB + change.

About 15 years ago Apple made a change in the OS to show storage capacities in decimal, turning 512GB into 500GB. Problem is, the marketing folks of the various manufacturers don't want to show 500GB on their ads when everyone else is showing the binary value of 512GB, so here we are. Fortunately nobody puts 1.099TB on their marketing materials, so everyone just uses the decimal 1TB.

 

[joevt]

About 15 years ago Apple made a change in the OS to show storage capacities in decimal, turning 512GB into 500GB. Problem is, the marketing folks of the various manufacturers don't want to show 500GB on their ads when everyone else is showing the binary value of 512GB, so here we are. Fortunately nobody puts 1.099TB on their marketing materials, so everyone just uses the decimal 1TB.

512GiB in decimal is 549.76 GB.

 

[dmr727]

512GiB in decimal is 549.76 GB.

Huh. I see it like @Basic75 above - 512GB * ( 1000/1024 )^3 = 477GB. Just marketing.

 

[Kinetic Motion]

here's a simple explanation : system resource's including and OS historically will use 12 - 20 gigs of HDD space same in linux , PC ,
online , or external drive is the option

 

[Kinetic Motion]

I bought a western digital black = gaming systems and a blue for media with enclosure SSD !

 

[Adora]

I grew up with all those numbers from (640) 1, 2, 4, 8, 16, 32... to 65.536. I knew them all by heart.

I don't like it was changed. It's really confusing.

I put an old 16MB SD-Card into my reader lately and it had only 13.9MB in Disk Utility.

For newer drives the producers/sellers I think were forced to gave the correct number. So they made them just bigger.