Anatomy of a Motherboard

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Anatomy of a Motherboard
http//www.gup20.com/images/motherboard.jpg
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Introduction to Motherboards

• A motherboard is also known as a mainboard or a
  mobo in web slang
• Motherboard complexity has been driven by
• changes in the various system buses
  (connectivity)
• changes in CPU (processor) speed
• the integration of system devices
• Sound, LAN, Video, USB2, IDE/PATA, SATA, FireWire
• Now appearing Bluetooth, WiFi, 7.1 surround
  sound, eSATA

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Hierarchical Storage (background)

• Fastest to slowest-
• Registers (variables) inside the processor very
  few
• Level 1 cache RAM kilobytes
• Level 2 cache RAM megabytes
• Main RAM gigabytes
• Flash RAM gigabytes
• Hard Disc storage many gigabytes
• DVD storage a few gigabytes each, but very cheap

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The Early 1980s

• The first IBM PC had a very simple motherboard
• The CPU, RAM and buses ran at 4.77MHz slow!
• CPU buses 8-bit data, 20-bit address (1MB RAM)
• The memory was 8 bits wide
• Peripherals were all 8-bit devices
• There was one data bus, joining the CPU to the
  RAM, ROM, support logic (no chipsets yet) and
  the expansion connectors.

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The PC/AT

• The IBM PC/AT originally used a 6MHz 80286 chip,
  rapidly upgraded to 8MHz.
• The 286 is a 16-bit device with a 24-bit address
  bus (16MB RAM).
• The AT introduced a 16-bit expansion bus but kept
  some 8-bit connectors.
• The whole motherboard ran at full processor speed.

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Fast PC/AT motherboards

• Processor speeds increased but the AT bus (later
  called the ISA bus) was fixed at 8MHz.
• This led to a separation of CPU speed and
  expansion bus speed.

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Fast PC/AT motherboards

• Later (about 1987) the i386 became available,
  with a 32-bit data bus. It could run faster than
  the normal type of RAM!
• The glue chipset connects to the various buses
  (16 and 32-bit) at various speeds
• This glue logic hides a lot of complexity

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• Block diagram of a typical Intel motherboard
• Note implied speed difference between North and
  South bridges

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Modern systems - common figures

• RAM runs at 100MHz to 500MHz
• DDR-400 is 200MHz RAM
• DDR2-800 is 400MHz RAM
• The PCI expansion bus runs at 33MHz for a total
  of about 1Gbps (one gigabit per second)
• The PCI-e expansion bus runs at 2.5Gbps per lane
  with up to 32 lanes per device!
• PCI-e version 2 is twice as fast

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Cache

• It is possible to design RAM to run at any
  possible CPU speed (gigahertz)
• But cheap mass-market RAM runs at just 400MHz
  (DDR2-800 aka PC6400 RAM)
• Typical systems use 256KB to 2MB of very fast
  cache RAM as a buffer between the CPU and the
  relatively slow main RAM
• This is a bit like a shop having items on the
  shelves rather than in the warehouse...

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Sockets and Cooling

• A CPU running at 4.77MHz gets warm
• A CPU running at 3GHz will quickly melt unless it
  is well cooled
• Heatsink fan HSF combinations are very
  important in desktop systems and can be very
  noisy

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Sockets and Slots

• The original Pentium class CPUs used Socket 7
• In 2004, Intel processors used Socket 478 and
  604 with Socket 370 just going
• By 2006, Intel was using Socket 775

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Sockets and Slots

• In 2004, AMD CPUs used Socket A and Socket 754,
  with Socket 940 and Socket 939 starting to be
  very important
• By 2006, AMD was phasing out Socket 939 and had
  introduced Socket AM2 and Socket 1204!
• The trend is clear motherboard and processor
  development is continuing apace
• See http//www.gup20.com/motherboards.htm