INTRODUCTION - Structured Computer Organization - page 42

well known that the marketing people wanted to keep it, and the new chip was call-
ed the Pentium Pro. Despite the small name change from its predecessor, this
processor represented a major break with the past. Instead, of having two or more
pipelines, the Pentium Pro had a very different internal organization and could ex-
ecute up to five instructions at a time.
Another innovation found in the Pentium Pro was a two-level cache memory.
The processor chip itself had 8 kilobytes of fast memory to hold commonly used
instructions and another 8 kilobytes of fast memory to hold commonly used data.
In the same cavity within the Pentium Pro package (but not on the chip itself) was
a second cache memory of 256 kilobytes.
Although the Pentium Pro had a big cache, it lacked the MMX instructions
(because Intel was unable to manufacture such a large chip with acceptable yields).
When the technology improved enough to get both the MMX instructions and the
cache on one chip, the combined product was released as the Pentium II. Next, yet
more multimedia instructions, called SSE ( Streaming SIMD Extensions ), were
added for enhanced 3D graphics (Raman et al., 2000). The new chip was dubbed
the Pentium III, but internally it was essentially a Pentium II.
The next Pentium, released in Nov. 2000, was based on a different internal ar-
chitecture but had the same instruction set as the earlier Pentiums. To celebrate
this event, Intel switched from Roman numerals to Arabic numbers and called it
the Pentium 4. As usual, the Pentium 4 was faster than all its predecessors. The
3.06-GHz version also introduced an intriguing new feature—hyperthreading.
This feature allowed programs to split their work into two threads of control which
the Pentium 4 could run in parallel, speeding up execution. In addition, another
batch of SSE instructions was added to speed up audio and video processing even
more.
In 2006, Intel changed the brand name from Pentium to Core and released a
dual core chip, the Core 2 duo . When Intel decided it wanted a cheaper sin-
gle-core version of the chip, it just sold Core 2 duos with one core disabled be-
cause wasting a little silicon on each chip manufacturered was ultimately cheaper
than incurring the enormous expense of designing and testing a new chip from
scratch. The Core series has continued to evolve, with the i3, i5, and i7 being pop-
ular variants for low-, medium-, and high-performance computers. No doubt more
variants will follow. A photo of the i7 is presented in Fig. 1-12. There are actually
eight cores on it, but except in the Xeon version, only six are enabled. This ap-
proach means that a chip with one or two defective cores can still be sold by dis-
abling the defective one(s). Each core has its own level 1 and level 2 caches, but
there is also a shared level 3 (L3) cache used by all the cores. We will discuss
caches in detail later in this topic.
In addition to the mainline desktop CPUs discussed so far, Intel has manufac-
tured variants of some of the Pentium chips for special markets. In early 1998,
Intel introduced a new product line called the Celeron , which was basically a low-
price, low-performance version of the Pentium 2 intended for low-end PCs. Since