This is normal, and enters into one of the longest-running confusions known 🙂
Your drive is 80GB in size, as you've probably seen advertised. In reality there is a little extra spare flash in reserve which i think is quoted at an extra 7-10%, but isn't 'user accessible'. It's used by the drive for 'maintenance' purposes.
so for user-accessible, that's:
There's a difference between the metric and binary definitions (SI and IEC); 1GB = 1000MB, and 1GiB = 1024MB. HDD manufacturers have traditionally used metric defintion of 1GB = 1000 MB, and it's sort of stuck. Windows on the otherhand uses the notion/defintion that 1024 bytes makes up 1KiB.
So basically, there's nothing wrong. If in doubt of any drive, try and find out what the drive size is in bytes and you can work it out from there. Afterall, that's one things the manufacturers have a consensus on, that there's 8 bits in a byte
Your experience is normal. The SSDs are following the hard drive convention, where a GB = 1 billion bytes. Microsoft is using the binary convention where a GB = 2^30 bytes (1,073,741,824). To distinguish the two, a new convention for the binary counting is called a "gibibyte", abbrevaiated "GiB".
Interestingly, if you read some other websites where they open up the X-25, you can see that there is actually 80 (binary) GiB of Nand flash inside. Only the 80 (decimal) GB is made available to the user. This 7% difference is used for management and overhead by the controller.
The actual number of "logical block addresses" or LBAs available to the user is actually determined by a standards body called IDEMA. So Intel is following the IDEMA standard for an 80GB hard drive, in terms of size available.