usb-a to usb-c

USB-A is the shape of the rectangular, non reversible connector. It does not determine the speed of the transfer. There are several different USB SPEEDS associated with the identical-looking USB-A shaped connectors.

The original has four conductors on one side of the plug or jack, and a plastic alignment plug that is a neutral color such as white or black.. It can attain USB-2 speeds of up to theoretical 480 M bits/second or 60 M Bytes/sec (actual speeds vary). This is slower than the top speeds attainable by all but slow Rotating drives, so it can present a bottleneck.

USB-3.x "SuperSpeed" added five more conductors to the connector, situated deeper inside the extended length plug and jack. This allows the data to go 'double-rail' or 'Push-pull' drivers and receivers for higher speeds with better noise immunity. Some are also Full duplex, but this does not have much of an impact from most transfers. Advanced versions can use two channels for even faster speeds.

These plugs and jacks are often coded with a blue plastic insert. (But Apple does NOT follow this Blue insert convention.) They are able to attain nominal 5 Giga bits/sec or as high as theoretical 500 M Bytes/sec, so not a serious bottleneck to most SSD drive transfers.

Much more info is available:

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

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Hi,

It's a USB-A speed of data transfer.

"They" aren't really correct. USB-C and USB-A are plug/connector types (as is USB-B and the various mini and micro versions of -A and -B), not transfer protocols. Transfer speeds are determined by the USB standard, e.g. USB 1.1, USB 2.0, USB 3.0, USB 3.1, etc.

USB-A connectors can be 1.0 and up, USB-C connectors can be USB 2.0 and up but are generally USB 3.0 or 3.1. Thunderbolt 3 is equivalent to USB 4.0 and uses the same physical plug as USB-C.

Max speeds are:

• USB 1.1 - 12 Mbps
• USB 2.0 - 480 Mbps
• USB 3.0 - 5 Gbps (~10x faster than USB 2.0)
• USB 3.1 - 10 Gbps
• TB3 - 40 Gbps

For USB-A ports, you can tell the standard by the color of the plastic bar in the port – white is USB 1, black is USB 2, and blue is USB 3 (but you'd need to look at the drive specs to see if it is USB 3.0 or 3.1).

So, if your drive has a blue USB-A port you can get 5 or 10 Gbps max speed, if it's black you can only get 480 Mbps max speed.

However, if your external drive is a regular HDD (with a magnetic disk inside spinning at 5400 or 7200 rpm), the average data transfer speed off the drive is ~800 Mbps for 5400 rpm and 1.2 Gbps for 7200 rpm. Thus, if your drive is USB 3 the limiting factor is the drive itself, not the USB connection.

Elizalde_06 wrote:

they say usb-c is faster than usb-a, and my mac only has usb-c ports. If I use a dongle to connect a hard drive with usb-a, which am I actually using the usb-a or usb-c? So I can see the speed of data transfer

This is what they call backwards compatible. Negotiated at " USB-a " speed.

This is the way it has always worked.

The speed will be the spedd of the slowest device in the chain. Devices/connections can go slower but you can't make them go faster.

If the cable/adapter you selected has enough conductors, it COULD support up to USB-3 speeds, but if it does not have all the conductors present, it can not possibly run faster than USB-2 speeds.