Could USB ever take over PCI Post: 302866215

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Special Forums Hardware Could USB ever take over PCI Post 302866215 by lupin..the..3rd on Monday 21st of October 2013 01:44:50 PM

10-21-2013

Registered User

Quote:

Originally Posted by Lost in Cyberia

Internally speaking, for your motherboard bus. Would it be possible for a usb standard to be used in place of the PCI or PCIe bus that is now nearly standard on all PC's? If not, why wouldn't this work?

It would not work for several reasons.

Firstly USB does not support DMA transfer modes. USB operates only in PIO mode, which is crufty and old and slow. PATA, SATA, Firewire, SCSI all operate in DMA mode, which is the biggest factor for why they are so much faster interfaces for attaching hard drives than USB.

Secondly USB has very high protocol overhead and poor performance with bulk data transfers. For example, USB 2.0 has a raw bitrate of 480 Mbits/s. That is 60 MB/s. Yet anyone who's used a USB hard drive knows that even on the newest fastest computers, real world USB 2.0 transfer rates are barely over 30 MB/s. I.e. USB can barely achieve 50% efficiency. Firewire, SCSI, SATA/PATA, on the other hand, achieve 90%+ of their raw bitrate in real world performance.

Another point worth mentioning is the abysmal bus power provided by USB. Only 500 mW. It's the worst of all external peripheral busses. Firewire has been providing 3x the bus power for many years now as compared with USB. And since you're evaluating it as a replacement for PCI-E, which carries 75w, you can see that you'd need about 150 USB ports to provide the bus power of a single PCI-E slot.

Lastly USB performs very poorly at isochronous transfers. Isochronous transfers are critical for audio and video work, where precise timing is key. This is why all Pro Audio/Video gear has been on Firewire for many years, instead of USB, because even though the USB standard includes isochronous support, it's a hack, and doesn't work very well in the real world.

USB was originally designed as a replacement for the RS232 serial port, PS/2 keyboard and mouse port, and the joystick port. All very low speed serial devices. And USB works quite well for these devices. For high bitrate bulk data transfers, low latency, etc. USB is a real turd.

As for one replacing the other, if anything, its the other way round. Look at Thunderbolt. It's essentially an external PCI-E, and as you might expect, it performs leagues ahead of USB for bandwidth intensive devices like hard disks or VGA displays.

Last edited by lupin..the..3rd; 10-21-2013 at 04:15 PM..

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LEARN ABOUT PHP

usb_as

usb_as(7D)							      Devices								usb_as(7D)

NAME

       usb_as - USB audio streaming driver

SYNOPSIS

       sound@unit-address

DESCRIPTION

       The usb_as driver is a USBA (Solaris USB Architecture) compliant client driver that supports the USB Audio Class 1.0 specification.

       The  usb_as  driver processes audio data messages during play and record and sets sample frequency, precision, encoding and other functions
       on request from the USB audio control driver. See usb_ac(7D).

       This driver is plumbed under the USB audio control driver and does not directly interface with the user application.

FILES

       /kernel/drv/usb_as

	   32-bit x86 ELF kernel module

       /kernel/drv/amd64/usb_as

	   64-bit x86 ELF kernel module

       /kernel/drv/sparcv9/usb_as

	   64-bit SPARC ELF kernel module

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+------------------------------+
       |      ATTRIBUTE TYPE	     |	     ATTRIBUTE VALUE	    |
       +-----------------------------+------------------------------+
       |Architecture		     |SPARC, x86, PCI-based systems |
       +-----------------------------+------------------------------+
       |Availability		     |SUNWusb			    |
       +-----------------------------+------------------------------+
       |Stability level 	     |Evolving			    |
       +-----------------------------+------------------------------+

SEE ALSO

       mixerctl(1), attributes(5), usba(7D), usb_ac(7D), audio(7I), mixer(7I), streamio(7I)

       Writing Device Drivers

       Universal Serial Bus Specification 1.0 and 1.1

       System Administration Guide: Basic Administration

       http://www.sun.com/io

DIAGNOSTICS

       In addition to being logged, the following messages may appear on the system console. All messages are formatted in the following manner:

       Warning: <device path> (usb_as<instance num>): Error Message...

       where <device path> is the physical path to the device in /devices directory.

       No bandwidth available.

	   There is no bandwidth available for the isochronous pipe. As a result, no data will be transferred during play and record.

       Operating a full/high speed audio device on a high speed port is not supported.

	   The USB software does not currently support full or high speed audio devices connected to an external USB 2.0 hub that is linked  to  a
	   port of a USB 2.0 host controller. Audio devices must be connected directly to a port of a USB 2.0 controller or to any USB 1.1 port.

       Cannot access device. Please reconnect <name>.

	   There was an error in accessing the device during reconnect. Please reconnect the device.

       Device is not identical to the previous one on this port. Please disconnect and reconnect.

	   A  USB  audio  streaming interface was hot-removed while open. A new device was hot-inserted which is not identical to the original USB
	   audio device. Please disconnect the USB device and reconnect the device to the same port.

NOTES

       The USB audio streaming interface will be power managed if the device is idle.

SunOS 5.10							    9 Oct 2004								usb_as(7D)