hard drive sata connections

[TheBean]

why do hard drives and some ssd's use the sata connection. why cant every connection in a system just use usb ports. like the front panel connectors have so many different wires like the led and the power button. why cant they just plug into a usb port which can make everything easier.

 

sorry if its unclear to understand

[Mira Yurizaki]

SATA has the following advantages over USB, at least when it was developed way back when (what was it, 2004?)

• USB back then was limited to 480Mbps (or 60 megabytes per second). After overhead, it's really more like 40 megabytes per second on a good day. IDE's maximum speed was 133 megabytes per second. SATA's first generation is 150 megabytes per second.
• USB 2.0 and earlier is single duplex. To a storage drive, that means you can only read or write. Granted, while they probably don't do both at the same time anyway, you couldn't for example, issue more commands to the drive while you were reading something.
• Purpose built protocol for storage drives. Technically you could do a USB to SATA but that's still overhead
  • I'm also not sure how complicated the USB protocol is, but I'm sure it's more complicated than SATA due to USB's more generic purpose nature.

Edited March 28, 2018 by M.Yurizaki
Added note about USB's megabits to megabytes.

[owencrispy]

9 minutes ago, M.Yurizaki said:

SATA has the following advantages over USB, at least when it was developed way back when (what was it, 2004?)

• USB back then was limited to 480Mbps. After overhead, it's really more like 40 megabytes per second on a good day. IDE's maximum speed was 133 megabytes per second. SATA's first generation is 150 megabytes per second.
• USB 2.0 and earlier is single duplex. To a storage drive, that means you can only read or write. Granted, while they probably don't do both at the same time anyway, you couldn't for example, issue more commands to the drive while you were reading something.
• Purpose built protocol for storage drives. Technically you could do a USB to SATA but that's still overhead
  • I'm also not sure how complicated the USB protocol is, but I'm sure it's more complicated than SATA due to USB's more generic purpose nature.

Jus happened to be browsing and found that these are some things I didnt know! Thank you for the information!

[mariushm]

28 minutes ago, saksham said:

why do hard drives and some ssd's use the sata connection. why cant every connection in a system just use usb ports. like the front panel connectors have so many different wires like the led and the power button. why cant they just plug into a usb port which can make everything easier.

 

sorry if its unclear to understand

SATA was launched in 2000 and was designed from the start for 1.5 gbps (150 MB/s transfer speed) and because it was meant for internal connections it has some limitations (like 30-45 cm cable length)

 

USB was launched in 1996 and was initially just 12 mbps. It was meant for peripherals and designed to work with longer cables (up to around 3m) and with the expectations that the quality of the cables would vary so it was made to be more resilient to bad quality cables (so even cheap chinese usb cables would work) and it was also designed from the start with the idea of easy disconnect and reconnect (devices could be unplugged or reconnected often being peripherals). SATA has some hot plug and play but often these features were unreliable and they didn't catch on much outside servers etc.

 

Only in 2000, USB 2.0 came with more features and with ability to work at 480 mbps but that's maximum theoretical and half duplex - in real world, the maximum possible speeds are around 35 MB/s in either direction.

 

SATA was meant to be a replacement for IDE which used flat ribbon cables with up to 80 wires, that limited the transfer speeds to maximum 133 MB/s (100 MB/s on Intel systems)

As tech improved, they managed to increase the speed to 3 gbps (~ 285 MB/s) and now the latest version runs at 6 gbps (around 550MB/s because the transfers use 8:10 encoding, so 20% of the bits of those 6gbps are used for error correction)... pretty much with the same wires inside the cables and same limitations (around 30-45cm of cable)

 

USB uses more processor power to transfer data because it's designed in a different way.... for example USB uses the concept of polling ... a certain number of times a second (from 125 to 1000 times a second) the usb controller asks the device plugged in the connector "do you have data to give me?" (like key presses, mouse movement, video frames from a tv tuner) and the device replies no or yes and then sends data. The USB device (usually) is not allowed to initiate communication with the usb controller, it has to wait and be asked.

SATA has no such limitation, the sata controller can send commands and the device can at any time send commands to the sata controller, and the sata controller can request data thousands of times a second from the device.

 

Now there's the tendency to move from SATA to m.2 , which uses pci-e lanes, you can use a single pci-e x1 lane, 2 lanes or 4 lanes to connect your m.2 device to the pc ... so instead of having a separate sata controller in the chipset you could replace that with a "pci-e switch" that let's say takes in 4-8 pci-e lanes and creates 16-32 pci-e lanes, so you'd be able to group 1,2,4 lanes at a time to create your m.2 connectors for various drives.