What the difference between NVME and m.2

[TheOnlyXenoT_T]

Hey i was wondering what the difference between NVME and m.2 or is there any ?

[seagate_surfer]

Hello TheOnlyXenoT_T,

 

One is the standard and the other one is the form factor, you can check out more in deep the fundamentals of the NVME interface and the hard drive sizes like M.2 in these links:

• https://en.wikipedia.org/wiki/M.2
• https://en.wikipedia.org/wiki/NVM_Express

[Fasauceome]

M.2 is the physical form factor. NVMe is a transfer protocol. The alternative to m.2 is SATA, and the alternative to NVMe is AHCI.

[TheOnlyXenoT_T]

So M.2 are the small little sticks and NVME is like the software under it or am i just plain stupid feel free to correct me

[YedZed]

M.2 = connector

NVME = protocol

See Fasauceome

[YedZed]

Just now, TheOnlyXenoT_T said:

So M.2 are the small little sticks and NVME is like the software under it or am i just plain stupid feel free to correct me

Yeah basically. 

Very low-level software though. More like firmware.

[TheOnlyXenoT_T]

Alright thanks for the Info

 

[mariushm]

m.2 is the connector, which has the contacts for a pci-e v3.0 x4 "slot" , a SATA connection and other things (usb).

A m.2 device can use either sata or pci-e side of the connector for communication.

 

Some budget SSDs may only use the SATA part of the connector for communication, which means max ~ 550-580 MB/s instead of up to ~4 GB/s.

 

[YedZed]

45 minutes ago, mariushm said:

Some budget SSDs may only use the SATA part of the connector for communication, which means max ~ 550-580 MB/s instead of up to ~4 GB/s.

 

wait, isn't a SATA 3 slot rated at 6gp/s? Or is that gigabit?

[mariushm]

34 minutes ago, YedZed said:

wait, isn't a SATA 3 slot rated at 6gp/s? Or is that gigabit?

 

sata 3 is 6 gbps

 

6gbps means 6 billions of bits per second going through the cable.

 

There's 8 bits in each byte, so that's 750,000,000 bytes per second.

But, for every 8 bits of actual data, there's 2 bits used for error correction, so you actually have a maximum theoretical of  750,000,000 x  8 / 10 = 600,000,000  bytes per second of USABLE DATA.

 

If you use multiples of 1024 as Windows uses when it shows the amount of disk space used, that means a maximum theoretical of 585,937 KiB/s or 572.204 MiB/s

 

But note that just like with USB and other protocols, there's overhead.. there's communication between the sata controller and the drive besides raw data being transferred ( give me data that's in sector 123456 and keep going, ok sent you the data, ok i got the data) and some data "packets" must be a certain fixed size, so there's a few bytes of padding (filler bytes, unused) and so on.... so for very long single file transfers this overhead is very small, for a lot of small files this overhead can be more substantial (but still small, let's say less than a megabyte per second out of <600 megabytes per second)

 

Basically, 6 gbps means you can reach around 550-580 MB/s.

 

USB is even worse, it's practically impossible to actually reach 480mbps (for usb 2.0) or 5 gbps (for usb 3.0) due to the way data is arranged in packets and sent through the cable.. even though physically the wires can transfer 5 gbps worth of bits, by design a device can't really figure out a way to arrange the data it sends to the usb controller in a way that would make it possible to reach that 5 gbps limit. If my memory is correct, I think the maximum possible for usb 3.0 was somewhere around 4.7 gbps

 

ps.  The nvme (pci-e) portion of the m.2 connector can use pci-e v2.0 lanes (500 MB/s per lane) or pci-e v3.0 lanes (~970 MB/s per lane max)  so a SSD connected to a m.2 connector could have a maximum of 2 GB/s if the lanes are v2.0 , or could have up to nearly 4 GB/s speed.

 

There's also SSDs that can use only 1 pci-e lane out the maximum 4 in the m.2 connector, or on some motherboards you can reduce the number of lanes in the m.2 connector from 4 to a lower number, in order to enable other pci-e slots or give more lanes to other devices on the motherboard.

 

For example if you have a 512 GB TLC drive and you know you won't read and write from it at 2 GB+/s you may want to artificially restrict it to pci-e v3.0 x1 which would still give you up to 1 GB/s in speed.

 

[YedZed]

3 minutes ago, mariushm said:

 

sata 3 is 6 gbps

 

6gbps means 6 billions of bits per second going through the cable.

 

There's 8 bits in each byte, so that's 750,000,000 bytes per second.

But, for every 8 bits of actual data, there's 2 bits used for error correction, so you actually have a maximum theoretical of  750,000,000 x  8 / 10 = 600,000,000  bytes per second of USABLE DATA.

 

If you use multiples of 1024 as Windows uses when it shows the amount of disk space used, that means a maximum theoretical of 585,937 KiB/s or 572.204 MiB/s

 

But note that just like with USB and other protocols, there's overhead.. there's communication between the sata controller and the drive besides raw data being transferred ( give me data that's in sector 123456 and keep going, ok sent you the data, ok i got the data) and some data "packets" must be a certain fixed size, so there's a few bytes of padding (filler bytes, unused) and so on.... so for very long single file transfers this overhead is very small, for a lot of small files this overhead can be more substantial (but still small, let's say less than a megabyte per second out of <600 megabytes per second)

 

Basically, 6 gbps means you can reach around 550-580 MB/s.

 

USB is even worse, it's practically impossible to actually reach 480mbps (for usb 2.0) or 5 gbps (for usb 3.0) due to the way data is arranged in packets and sent through the cable.. even though physically the wires can transfer 5 gbps worth of bits, by design a device can't really figure out a way to arrange the data it sends to the usb controller in a way that would make it possible to reach that 5 gbps limit. If my memory is correct, I think the maximum possible for usb 3.0 was somewhere around 4.7 gbps

Wow, that was a long and well drawn out explanation. !givegold