Getting 18-22 mBps while transferring any data in the same hard drive

its a Seagate 2TB 5900 rpm drive. Model no. is ST2000VM002-9UY166 2000.3 GB.
Whenever I start transferring, I get about 70-80 mBps for the first few seconds but then it drops down to a constant 18-22mBps.
I am not copying huge amounts of small files. I am copying individual big videos or iso files.
The task manager shows about 50 mBps at 100% disk usage as I am writing and reading from the same disk. I used crystaldisk mark 5 and I got significantly better results. The results are shown below.


I guess I am having this problem since I bought it just a few weeks ago.

I have an external usb 3.0 hard drive and I get about 40 mBps read as well as write speed on it. It doesn't matter if I connect it to a usb 3 port or usb 2 port.

I checked for the DMA thing but I couldn't find any channels in the IDE ATA/ATAPI controllers section. I just see controller for my hard drive.
I tried searching for some related stuff in bios but all I found was that my hard drive was set to AHCL mode or whatever it is.
I even tried changing the sata port to which the hard drive was connected in my motherboard.
The results of crystaldisk info are shown below-

Any help would be highly appreciated.

The term of 70-80 mBps may be incorrect, probably is Mbps where small b = bits and capital B = Bytes. There's 8 bits in a Byte, 1024 Bytes in a KiloByte/KB, 1024KiloBytes in a MegaByte/MB, 1024 MB in a Gigabyte/GB and so on. kilobytes to megabytes at DuckDuckGo
The meaning of b and B goes way back in computing, my first experience with it was in the late '80s when first learning about computers.

Berton said:

The term of 70-80 mBps may be incorrect, probably is Mbps where small b = bits and capital B = Bytes. There's 8 bits in a Byte, 1024 Bytes in a KiloByte/KB, 1024KiloBytes in a MegaByte/MB, 1024 MB in a Gigabyte/GB and so on. kilobytes to megabytes at DuckDuckGo
The meaning of b and B goes way back in computing, my first experience with it was in the late '80s when first learning about computers.

Thanks for your reply.
I know the bits and bytes stuff. I really meant 70-80 megabytes per second. I have only talked in bytes everywhere.
Do you think 70-80 mBps in a 5900 rpm hard disk are not possible? If not then how much do you think is normal?

MhdHaris said:

Thanks for your reply.
I know the bits and bytes stuff. I really meant 70-80 megabytes per second. I have only talked in bytes everywhere.
Do you think 70-80 mBps in a 5900 rpm hard disk are not possible? If not then how much do you think is normal?

Don't I wish back in MS-DOS and Windows 3.xx days and a 120MB HDD that were true but mechanically I see no way to have had such a large number. Publishing has taken it upon themselves to confuse b with B, see it every day in all types of tech advertising, service manuals, etc.

As far as the drop in speed, we've seen that happen in data transfer whether within a computer, between computers or on the Internet where a download starts strong then drops down. Kinda like the difference between a quarter horse built for a quarter mile run or the 1 and 1/8 mile races for other horse breeds as use in the Kentucky Derby.

Berton said:

Don't I wish back in MS-DOS and Windows 3.xx days and a 120MB HDD that were true but mechanically I see no way to have had such a large number. Publishing has taken it upon themselves to confuse b with B, see it every day in all types of tech advertising, service manuals, etc.

As far as the drop in speed, we've seen that happen in data transfer whether within a computer, between computers or on the Internet where a download starts strong then drops down. Kinda like the difference between a quarter horse built for a quarter mile run or the 1 and 1/8 mile races for other horse breeds as use in the Kentucky Derby.

So do you mean that it is normal?

cereberus said:

Actually this sounds about right. Think of what you are doing.

Your slow speed is a consequence of reading and writing to same drive.

You are reading data from a drive over one disk data channel, and then writing it elsewhere on same data channel (it is a bit like being on a road where one lane is blocked off and each direction has to access other lane alternately which is obviously much slower made worse as cars have to wait for traffic to start moving from standstill and do not accelerate to normal speed as cars are bunched up).

So at best you can only get half the speed. It is made much worse because disk heads have to keep moving back and forth as well.

Sure you can get high speeds if you were using two drives eg read from ssd on its data channel, and write to hdd on its channel (so data is all one way and head is not bouncing back and forth).

The apparent initial burst of high speed is due to data being buffered but after a short periods buffers are full up.

I understand that but don't you think that 18-22mBps is little too low? I got over 100 mBps read as well as write speed in crystal disk mark so technically shouldn't I get about 50mBps even when I am reading and writing in the same disk and over 50 mBps when I am transferring data to/from my external usb 3.0 hard drive?