Hardware Reference
In-Depth Information
weretheslowest.IncludingL2insidetheprocessormadeitfaster,andincludingitdirectly
on the processor die (rather than as chips external to the die) is the fastest yet. Any chip
that has on-die full core speed L2 cache has a distinct performance advantage over any
chip that doesn't.
A third-level or L3 cache has been present in some processors since 2001. The first
desktop PC processor with L3 cache was the Pentium 4 Extreme Edition, a high-end chip
introduced in late 2003 with 2MB of on-die L3 cache. Although it seemed at the time that
this would be a forerunner of widespread L3 cache in desktop processors, later versions
of the Pentium 4 Extreme Edition (as well as its successor, the Pentium Extreme Edition)
dropped the L3 cache, instead using larger L2 cache sizes to improve performance. L3
cache made a return to PC processors in 2007 with the AMD Phenom and in 2008 with
the Intel Core i7, both of which have four cores on a single die. L3 is especially suited
to processors with multiple cores because it provides an on-die cache that all the cores
can share. Since 2009, L3 cache has become a staple in most processors with two or more
cores.
Thekeytounderstandingbothcacheandmainmemoryistoseewheretheyfitintheover-
all system architecture. See
Chapter 4
for diagrams showing recent systems with different
types of cache memory.
Memory Standards
For memory to be as inexpensive and interchangeable as possible, industry-standard spe-
cifications for both chips and modules have been developed. The Joint Electron Device
Engineering Council (JEDEC) Solid State Technology Association creates most industry-
standard memory chip and module designs.
JEDEC
JEDEC is the semiconductor engineering standardization body of the Electronic Industries
Alliance (EIA), a trade association that represents all areas of the electronics industry.
JEDEC, which was created in 1960, governs the standardization of all types of semiconduct-
or devices, integrated circuits, and modules. JEDEC has about 300 member companies, in-
cludingmemory,chipset,andprocessormanufacturersandpracticallyanycompanyinvolved
in manufacturing computer equipment using industry-standard components.
TheideabehindJEDECissimple:Ifonecompanyweretocreateaproprietarymemorytech-
nology, for example, then other companies that wanted to manufacture components compli-
ant with that memory would have to pay license fees, assuming the company that owned it
was interested in licensing at all! Parts would be more proprietary in nature, causing prob-
lems with interchangeability or sourcing reasonably priced replacements. In addition, those
companies licensing the technology would have no control over future changes the owner
company made.
