SSD + Elementary OS = Speed?

Question

linux

Good day.
Source:
There is an asus k40ab laptop , a crucial m550 was installed instead of the HDD. And also installed Elementary OS. And encryption is enabled at the OS level.
Test
Recording

sync; dd if=/dev/zero of=tempfile bs=1M count=1024; sync
1024+0 records in
1024+0 records out
1073741824 bytes (1,1 GB) copied, 19,7391 s, 54,4 MB/s

Reading

/sbin/sysctl -w vm.drop_caches=3
dd if=tempfile of=/dev/null bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1,1 GB) copied, 16,9107 s, 63,5 MB/s

Another test

sudo hdparm -Tt /dev/sda
/dev/sda:
 Timing cached reads:   1890 MB in  2.00 seconds = 944.92 MB/sec
 Timing buffered disk reads: 644 MB in  3.01 seconds = 213.97 MB/sec

Q:
How true are these tests? And why do I get different results in different cases? Or is it the only way with my laptop data?
Answer:
The problem turned out to be really in the encryption. Rearranged the system.

sync; dd if=/dev/zero of=tempfile bs=1M count=1024; sync
1024+0 records in
1024+0 records out
1073741824 bytes (1,1 GB) copied, 3,43969 s, 312 MB/s
sudo /sbin/sysctl -w vm.drop_caches=3
dd if=tempfile of=/dev/null bs=1M count=10241024+0 records in
1024+0 records out
1073741824 bytes (1,1 GB) copied, 4,91821 s, 218 MB/s

Answer 1

Actually, "OS-level encryption" requires resources.
It is one thing to simply transfer data over the interface, and it is quite another to process and decrypt encrypted information.

Answer 2

Without delving into the numbers, it is clear that the laptop is not new, look at what SATA interface is on it and whether the SSD speed rests on it

Answer 3

The site says that read / write 550mbs.