Why are internal and external drives measured differently?

[Airlane1979]

I have a PC with a 1TB SSD. I bought a Toshiba 1TB HDD to back up the drive. Rookie mistake! I should have realised: a google search told me that internal drives are typically measured in base 10 (1GB = 1 billion bytes), while external drives are usually measured in base 2 (1GB = 1,073,741,824 bytes). Hence, the actual usable capacity of a 1TB external drive is lower than the advertised capacity. As I found when I compared them in File Explorer.

So, when I tried to back up 600GB of files using EaseUS Todo Backup Free, after it got to 76% (taking 6 hours) it stopped and demanded more space. Apparently, this is because the software is compressing the data which requires extra space while it's doing so... which means if I untick the Compress option before starting the whole backup again, it might get to the end.

Anyone else come across this problem?

 

[voyagerfan99]

That's not a thing. 1TB is 1TB. You're interpreting it wrong.

In computers, everything is stored in binary (base 2). This makes it convenient to use powers of 2 to express sizes and memory addresses. 1024 is 210, the power of 2 which is closest to 1000. So computer engineers used the term gigabyte to denote 1024 megabytes (as well as megabyte for 1024 kilobytes and kilobyte for 1024 bytes), because it was more convenient. Technically speaking it was incorrect, since kilo means 1000 and not 1024.

However, disk drive manufacturers chose to use the "standard" meaning of giga/mega/kilo, which means one gigabyte of hard drive space is 10003 bytes and not 10243.

In order to solve this confusion, the International Electrotechnical Commission decided that the base 2 terms would be renamed to "kibibyte", "mebibyte", "gibibyte" etc., however these terms have no completely caught on.

 

[beers]

There's no difference between internal and external drives, it's all just still binary. You can take a normal SATA drive and put it in an enclosure, bam it's an external drive.

You can use something like (1000/1024)^x*y to convert from base10 to base2 values, where x is your 'tier' for each grouped layer and y is the base10 capacity you want. x would be 1 for kilo, 2 for mega, 3 for giga, 4 for tera, etc.

Such as (1000/1024)^4*2 tells you a 2 terabyte drive nets you 1.818989404 TiB for tebibytes.
Conversely for you, (1000/1024)^3*1000 nets you the ~931 GiB you're observing on your drive.

As for the compression piece, the app should be compressing in RAM and then writing the compressed contents, taking up less space. I'd be taking a look at the data volume and the process ran. You could always compress an archive on local storage and transfer it after.