System Board
System Bus
Chapter 2
58
System Bus
The system bus of the Pentium IV processor is implemented in the Gunning Transceiver
Logic (GTL)+ technology. This technology features open-drain signal drivers that are
pulled up through resistors at bus extremities to the operating voltage of the processor
core. These resistors also act as bus terminators and are integrated in the processor and
in the 82850 MCH.
Figure 2-14 The System Bus
The supported operating frequency of the GTL+ bus for the Pentium IV is 100MHz. The
width of the data bus is 64 bits, whereas the width of the address is 32 bits. Data bus
transfers occur at four times the system bus, at 400MHz. Along with the operating
frequencies, the processor voltage is set automatically.
The control signals of the system bus allow the implementation of a “split -transaction”
bus protocol. This allows the Pentium IV processor to send its request (for example, for
the contents of a given memory address) and release the bus, rather than waiting for the
result. Therefore, processor can accept another request. The MCH, as the target device,
then requests the bus again when it is ready to respond, and sends the requested data
packet. As many as four transactions can be outstanding at any given time.
Intel Pentium IV Processor
The Pentium IV processor has several features that enhance performance:
• Data bus frequency of 400MHz
850
Memory
Controller Hub
(MCH)
82850
1.5V
AGP
Pro
Connector
I/O Controller Hub
(ICH) 82801AA
Dual Rambus channel
Address (32)
Control
Data (64)
AGP 4x Bus
(133MHz
(1GB/sec data
transfer rate)
Socket 423
100MHz two-way sys-
tem bus (data bus runs at
4 x 100MHz, 3.2GB/s
transfer rate)
HUB LINK 8
(266MB/s
data transfer
rate)
3.2GB/s at
400MHz data
transfer rate)
4 onboard RIMM
sockets
supporting
RDRAM memory
Intel Pentium IV
Processor
