Hardware Reference
In-Depth Information
more 8259As, allowing for up to 64 I/O devices in a two-stage interrupt network.
The Intel ICH10 I/O controller hub, one of the of the chips in the Core i7 chipset,
incorporates two 8259A interrupt controllers. This gives the ICH10 15 external in-
terrupts, one less than 16 interrupts on the two 8259A controllers because one of
the interrupts is used to cascade the second 8259A onto the first one. The 8259A
has a few pins devoted to handling this cascading, which we have omitted for the
sake of simplicity. Nowadays, the ''8259A'' is really part of another chip.
While we have by no means exhausted the subject of bus design, the material
above should give enough background to understand the essentials of how a bus
works, and how CPUs and buses interact. Let us now move from the general to the
specific and look at some examples of actual CPUs and their buses.
In this section we will examine the Intel Core i7, TI OMAP4430, and Atmel
ATmega168 chips in some detail at the hardware level.
The Core i7 is a direct descendant of the 8088 CPU used in the original IBM
PC. The first Core i7 was introduced in November 2008 as a four-processor
731-million transistor CPU running up to 3.2 GHz with a line width of 45 nanome-
ters. The line width is how wide the wires between transistors are (as well as being
a measure of the size of the transistors themselves). The narrower the line width,
the more transistors can fit on the chip. Moore's law is fundamentally about the
ability of process engineers to keep reducing the line widths. For comparison pur-
poses, human hairs range from 20,000 to 100,000 nanometers in diameter, with
blonde hair being finer than black hair.
The initial release of the Core i7 architecture was based on the ''Nahalem'' ar-
chitecture; however, the newest versions of the Core i7 are built on the newer
''Sandy Bridge'' architecture. The architecture in this context represents the inter-
nal organization of the CPU, which is often given a code name. Despite being gen-
erally serious people, computer architects will sometimes come up with very clever
code names for their projects. One of particular note was the AMD K-series archi-
tectures, which were designed to break Intel's seeming invulnerable hold on the
desktop CPU market. The K-series processors' code name was ''Kryptonite,'' a
reference to the only substance that could hurt Superman, and a clever jab at the
dominant Intel.
The new Sandy-Bridge-based Core i7 has evolved to having 1.16 billion tran-
sistors and running at speeds up to 3.5 GHz with line widths of 32 nanometers. Al-
though the Core i7 is a far cry from the 29,000-transistor 8088, it is fully backward
