Memory - Upgrading and Repairing PCs - page 317

speed because it is installed on the motherboard and is connected to the CPU bus. You typically find
the L2 cache physically adjacent to the processor socket in Pentium and earlier systems.
See the Chapter 3 section, “ Cache Memory , ” p. 53 .
In the interest of improved performance, later processor designs from Intel and AMD included the L2
cache as part of the processor. In all processors since late 1999 (and some earlier models), the L2
cache is directly incorporated as part of the processor die, just like the L1 cache. In chips with on-die
L2, the cache runs at the full core speed of the processor and is much more efficient. By contrast, most
processors from 1999 and earlier with integrated L2 had the L2 cache in separate chips that were
external to the main processor core. The L2 cache in many of these older processors ran at only half
or one-third the processor core speed. Cache speed is important, so systems having L2 cache on the
motherboard were the slowest. Including L2 inside the processor made it faster, and including it
directly on the processor die (rather than as chips external to the die) made it faster yet.
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. Figure 6.2 shows the L1/L2/L3 cache configuration as reported by CPU-Z ( www.cpuid.com )
for an Intel Core i5-3570K processor.
Figure 6.2. CPU-Z screenshots showing the CPU/Cache information for an Intel Core i5-3570K
processor.
The key to understanding both cache and main memory is to see where they fit in the overall system
architecture. See Chapter 4 for diagrams showing recent systems with different types of cache
memory.
Memory Standards