USB 2.0 vs. USB 3.0: Speed Comparison for Flash Memories and External HDDs

[mech-eng]

In flash memories or external HDDs there is a distinction as usb 2 or usb 3. USB 3.0 is faster than USB 2.0 in such devices. But what about the situation for SDD drives? Does this distinction apply to them, too?

Thank you.

 

[phinds]

In flash memories or external HDDs there is a distinction as usb 2 or usb 3. USB 3.0 is faster than USB 2.0 in such devices. But what about the situation for SDD drives? Does this distinction apply to them, too?

Thank you.

USB is a transfer mechanism. Any device that is capable of send/receive at USB3 speeds will be faster with USB3 than with USB2. It's irrelevant what KIND of device it is; it only matters what its transfer rates are. A device that can only send/receive at USB2 speeds will be no faster with USB3 than with USB2.

 

[jtbell]

But what about the situation for SDD drives?

Do you mean SSD (solid state drives)?

 

[mech-eng]

Do you mean SSD (solid state drives)?

Yes, a mistake. I thought they were solid state disk drive, but not.

Thank you.

 

[newjerseyrunner]

The SSD is capable of bandwidth way higher than both USB 2 and 3. You will be limited by your connection, not the drive. I would highly recommend properly connecting it via a SATA connector.

 

[mech-eng]

The SSD is capable of bandwidth way higher than both USB 2 and 3.

But isn't there a relation between bandwitdth and connection types, i.e USB types?

Thank you.

 

[phinds]

But isn't there a relation between bandwitdth and connection types, i.e USB types?

Thank you.

Absolutely not. That's like saying that the size of your water tank depends on how big your faucet opening is. The SSD has a much higher bandwidth than the USB2 or even USB3 connections and if you have a faster connection, it will handle it. Conversely, if you have a very slow external drive, hooking it up to a USB3 won't make it any faster.

 

[rcgldr]

The SSD is capable of bandwidth way higher than both USB 2 and 3. You will be limited by your connection, not the drive. I would highly recommend properly connecting it via a SATA connector.

Or better still, connect a SSD to the PCIe bus. Seagate makes PCIe SSD's with up to 8GB/s transfer rates.

 

[mech-eng]

Absolutely not. That's like saying that the size of your water tank depends on how big your faucet opening is. The SSD has a much higher bandwidth than the USB2 or even USB3 connections and if you have a faster connection, it will handle it. Conversely, if you have a very slow external drive, hooking it up to a USB3 won't make it any faster.

Then can we say that the bandwidth somebody can use is the lower one between the device and the connection type for the device and the PC? If the SSDs have a higher bandwidth than the all connection types, are SSDs using connections at a speed of connection's full speed?

 

[phinds]

Then can we say that the bandwidth somebody can use is the lower one between the device and the connection type for the device and the PC?

yes

If the SSDs have a higher bandwidth than the all connection types, are SSDs using connections at a speed of connection's full speed?

Not sure I understand the question, but if I do then yes, ANY device will attempt to communicate at the highest speed possible, but that may not be a continuous function, depending on the device and the connection. Some devices (I don't think SSD's are among them) are set to communicate at discrete bandwidths. (at least that used to be the case. I'm not really up on modern communications technology)

 

[mech-eng]

Not sure I understand the question, but if I do then yes, ANY device will attempt to communicate at the highest speed possible, but that may not be a continuous function, depending on the device and the connection. Some devices (I don't think SSD's are among them) are set to communicate at discrete bandwidths. (at least that used to be the case. I'm not really up on modern communications technology)

When transfering data via usb, windows can shows the speeds. In my cases, the speeds are not constant, they are frequently changing between a maximum value and a minumum value. Why is this the case? What is "discrete bandwidths"? Isn't a discrete bandwidth you used above is device's own bandwidth?

Thank you.

 

[phinds]

When transfering data via usb, windows can shows the speeds. In my cases, the speeds are not constant, they are frequently changing between a maximum value and a minumum value. Why is this the case?

Because the computer (and possibly the computer on the device) will be doing other things in addition to the transfer.

What is "discrete bandwidths"? Isn't a discrete bandwidth you used above is device's own bandwidth?

No, it is the communication device's bandwidth. Some devices (old dial-up modems come to mind) would transfer at a fixed rate, but if that didn't work it would drop down to a lower rate. There would generally be a handshake between devices to agree on a rate.

 

[mech-eng]

Because the computer (and possibly the computer on the device) will be doing other things in addition to the transfer.No, it is the communication device's bandwidth. Some devices (old dial-up modems come to mind) would transfer at a fixed rate, but if that didn't work it would drop down to a lower rate. There would generally be a handshake between devices to agree on a rate.

But there are two relevant devices, one is the storage which is pluged into the PC via a connection type and the other is connection type i.e the port and slots. Aren't we already discussing them and their bandwidths? So communication device's bandwidth is confusing to me. Would you please explain it?

Thank you.

 

[phinds]

But there are two relevant devices, one is the storage which is pluged into the PC via a connection type and the other is connection type i.e the port and slots. Aren't we already discussing them and their bandwidths? So communication device's bandwidth is confusing to me. Would you please explain it?

Thank you.

This thread started off discussing USB transfer mechanisms. That is a communication device. You have STORAGE <-> USB <-> COMPUTER. The USB is the communication device.

https://en.wikipedia.org/wiki/USB_communications_device_class

 

[sysprog]

In flash memories or external HDDs there is a distinction as usb 2 or usb 3. USB 3.0 is faster than USB 2.0 in such devices. But what about the situation for SDD drives? Does this distinction apply to them, too?

Thank you.

The question raises some complexities. The terms must be clarified and qualified before they can be used to convey appropriately precise and unambiguous information. This brief (3 pages) HP paper on USB 3.0 clarifies some of the characteristics (please note that bandwidth is expressed in bits, while throughput is expressed in bytes). This full-length (145 pages) Intel paper on IO interface architecture has more scope and is more in-depth. And this SNIA (Storage Networking Industry Association) short (28 pages) SSD performance primer is reasonably rigorous without being too dry.