Why does the system report 7.7Gb of total Ram when I installed 8Gb?

Why does the system report 7.7Gb of total Ram when I installed 8Gb? I'm using 14.04 on a Dell Vostro 2011

The BIOS will reserve some memory, as will the most primitive level of the kernel, including some for video, perhaps. What is reported to you via system-info (which I don't use) or free -m is what is left.
If you observe the entries in the /var/log/kern.log file from during boot, you will see many having to do with reserving memory and such, and finally, a summary line:

May  3 14:27:20 s15 kernel: [    0.000000] Memory: 15975452K/16472972K available (8029K kernel code, 1240K rwdata, 3736K rodata, 1424K init, 1292K bss, 497520K reserved, 0K cma-reserved)

My system claimed to have 8 GB (gigabyte) of RAM. Ubuntu says it has 7.7 GiB (gibibyte).

7.7 GiB (gibibyte) = 8.26781 GB (gigabyte)

8 Gb (gigabit) = 1 GB (gigabyte)