Hardware Reference
In-Depth Information
The big advantage of the design of Fig. 3-51 is that the CPU has an extremely
high bandwidth to memory using a proprietary memory bus; the PCI bus offers
high bandwidth for fast peripherals such as SCSI disks, graphics adaptors, etc.; and
old ISA cards can still be used. The USB box in the figure refers to the Universal
Serial Bus, which will be discussed later in this chapter.
It would have been nice had there been only one kind of PCI card. Unfortun-
ately, such is not the case. Options are provided for voltage, width, and timing.
Older computers often use 5 volts and newer ones tend to use 3.3 volts, so the PCI
bus supports both. The connectors are the same except for two bits of plastic that
are there to prevent people from inserting a 5-volt card in a 3.3-volt PCI bus or vice
versa. Fortunately, universal cards exist that support both voltages and can plug
into either kind of slot. In addition to the voltage option, cards come in 32-bit and
64-bit versions. The 32-bit cards have 120 pins; the 64-bit cards have the same
120 pins plus an additional 64. A PCI bus system that supports 64-bit cards can
also take 32-bit cards, but the reverse is not true. Finally, PCI buses and cards can
run at either 33 or 66 MHz. The choice is made by having one pin wired either to
the power supply or to ground. The connectors are identical for both speeds.
By the late 1990s, pretty much everyone agreed that the ISA bus was dead, so
new designs excluded it. By then, however, monitor resolution had increased in
some cases to 1600
1200 and the demand for full-screen full motion video had
also increased, especially in the context of highly interactive games, so Intel added
yet another bus just to drive the graphics card. This bus was called the
AGP bus
(
Accelerated Graphics Port bus
). The initial version, AGP 1.0, ran at 264
MB/sec, which was defined as 1x. While slower than the PCI bus, it was dedicated
to driving the graphics card. Over the years, newer versions came out, with AGP
3.0 running at 2.1 GB/sec (8x). Today, even the high-performance AGP 3.0 bus
has been usurped by even faster upstarts, in particular, the PCI Express bus, which
can pump an amazing 16 GB/sec of data over high-speed serial bus links. A mod-
ern Core i7 system is illustrated in Fig. 3-52.
In a modern Core i7 based system, a number of interfaces have been integrated
directly into the CPU chip. The two DDR3 memory channels, running at 1333
transactions/sec, connect to main memory and provide an aggregate bandwidth of
10 GB/sec per channel. Also integrated into the CPU is a 16-lane PCI Express
channel, which optimally can be configured into a single 16-bit PCI Express bus or
dual independent 8-bit PCI Express buses. The 16 lanes together provide a band-
width of 16 GB/sec to I/O devices.
The CPU connects to the primary bridge chip, the P67, via the 20-Gb/sec (2.5
GB/sec) serial direct media interface (DMI). The P67 provides interfaces to a num-
ber of modern high-performance I/O interfaces. Eight additional PCI Express lanes
are provided, plus SATA disk interfaces. The P67 also implements 14 USB 2.0 in-
terfaces, 10G Ethernet and an audio interface.
The ICH10 chip provides legacy interface support for old devices. It is con-
nected to the P67 via a slower DMI interface. The ICH10 implements the PCI bus,
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