Motherboard Expansion Slots and Bus Speeds - CompTIA A+ 220-801: 1.2

Bus architecture

• A Communication Path
• A city of technology
• Internal PC Growth
• Independent pathways
• System expansion
• additional capabilities 

The expansion bus

• "Width" in bits
• Big roads, little roads
• Width is changing to bandwidth

•  Clock speed of bus
• The expansion bus gets its own clock
• 1 MHz (megahertz) = 1 million cycles per second
• 1 GHz = 1000 MHz
• Clock speed does not necessarily equal transfer rate 
• DDR3 SDRAM can transfer 64 times the memory clock speed

Conventional PCI (Peripheral Component Interconnect)

• Created in 1994
• A common expansion interface
• 32-bit and 64-bit bus width
• Throughput varies by bus version
• 133 MB/s (32-bit at 33 MHz)
• 266 MB/s (32-bit at 66 MHz or 64-bit at 33 MHz
• 533 MB/s (64-bit at 66 Mhz)

 PCI 32-bit expansion card

PCI 64-bit expansion card

Mini PCI

• PCI for laptops
• Shrink it down for mobile use.
• Expand features of laptops
• Wifi, mobile broadband, etc

•  No access to the card
• It's inside the laptop
• Can't touch it

PCI-X (PCI eXtended)

• Designed for servers
• Higher Bandwidth
•  Four times the clock speed
• Built to handle higher speed, network, and storage
• 1,064 MB/s capacity
• THIS IS NOT PCI EXPRES (completely different)

PCI Express

• Also known as PCIe
• This is not (PCI-X)
• Not really a bus in the traditional sense
• Unidirectional serial "lanes"
• Slower devices don't slow down everyone
• One,two,four,eight,sixteen, or thirty-two full duplex lanes
• x1, x2, x4, x8, x16, x32
• "x" is pronounced "by"
• i.e., "by 4," "by 16"

PCI Express throughout

• Different versions of PCIe
• Improvement in speed with each iteration
• Per-lane throughput in each direction
• -v1.x: 250 MB/s
• -v2.x: 500 MB/s
• v3.0: 985 MB/s (8 GT/s)
• v4.0: 1969 MB/s (16 GT/s)

CNR ( Communications and Networking Riser)

•  Modular riser for networking, modem, audio, etc.

AGP ( Accelerated Graphics Port)

•  Almost always called AGP
• Designed to cover the gap between PCI and PCI Express
• Difficult to find AGP today

AGP Versions

• AGP 1x (266MB/s),
• AGP 2x (522MB/s)
• AGP 1.0, 3.3V
• AGP 4x (1.07 GB/s)
• AGP 2.0, 1.5v
• AGP 8x (2.1 GB/s)
• AGP 3.0, 0.8V