Hardware Reference
In-Depth Information
is the container for the chip die, which essentially seals it from the environment.
After the chips are bonded and packaged, final testing is done to determine both proper function and
rated speed. Different chips in the same batch often run at different speeds. Special test fixtures run
each chip at different pressures, temperatures, and speeds, looking for the point at which the chip
stops working. At this point, the maximum successful speed is noted and the final chips are sorted into
bins with those that tested at a similar speed.
One interesting thing about this is that as a manufacturer gains more experience and perfects a
particular chip assembly line, the yield of the higher-speed versions goes way up. So, of all the chips
produced from a single wafer, perhaps more than 75% of them check out at the highest speed, and
only 25% or less run at the lower speeds. The paradox is that Intel often sells a lot more of the lower-
priced, lower-speed chips, so it just dips into the bin of faster ones, labels them as slower chips, and
sells them that way. People began discovering that many of the lower-rated chips actually ran at
speeds much higher than they were rated, and the business of overclocking was born. Similarly, some
lower-cost multicore processors from AMD have the same physical number of cores as higher-cost
ones, but some cores are disabled during manufacturing.
Processor Re-Marking
Processor re-marking, the alterations of chip marking to make a slower chip masquerade as a faster
chip, was once a major problem when virtually all processors could be overclocked (run at faster
clock speeds than normal). However, with the advent of retail boxed processors, clock multiplier
locks in most models, and utility programs such as CPU-Z that can identify processor names and
features, processor re-marking is now minimal compared to its heyday over a decade ago.
To make sure your system has the processor you paid for, download and run a copy of CPU-Z
(
www.cpuid.com/softwares/cpu-z.html
). CPU-Z is the
de facto
standard for CPU identification and
feature display.
PGA Chip Packaging
Variations on the pin grid array (PGA) chip packaging have been the most commonly used chip
packages over the years. They were used starting with the 286 processor in the 1980s and are still
used today, although not in all CPU designs. PGA takes its name from the fact that the chip has a grid-
like array of pins on the bottom of the package. PGA chips are inserted into sockets, which are often
of a zero insertion force (ZIF) design. A ZIF socket has a lever to allow for easy installation and
removal of the chip.
Most original Pentium processors use a variation on the regular PGA called staggered pin grid array
(SPGA), in which the pins are staggered on the underside of the chip rather than in standard rows and
columns. This was done to move the pins closer together and decrease the overall size of the chip
when a large number of pins is required.
Figure 3.8
shows a Pentium Pro that uses the dual-pattern
SPGA (on the right) next to a Pentium 66 that uses the regular PGA. Note that the right half of the
Pentium Pro shown here has additional pins staggered among the other rows and columns.
