Datasheet

Chapter 1

Personal Computer System Components

but then no more. You had a new bug to keep the ROM bug company. Liken this to the burn-

ing of a CD-R. Don’t need it any longer? You’ve got a handy coaster. Following the PROM

came erasable PROM (EPROM), which was able to be erased using ultraviolet light and subse-

quently reprogrammed using the original programming device. These days, our ﬂash memory

is a form of electrically erasable PROM (EEPROM), which does not require UV light to erase

its contents, but rather a slightly higher than normal electrical pulse.

Although the names of these memory devices are different, they all contain

ROM. Therefore, regardless which of these technologies is used to manufac-

ture a BIOS chip, it’s never incorrect to say that the result is a ROM chip.

Memory Packaging

First of all, it should be noted that each motherboard supports memory based on the speed

of the frontside bus and the memory’s form factor. For example, if the motherboard’s FSB is

rated at a maximum speed of 533MHz, and you install memory that is rated at 300MHz,

the memory will operate at only 300MHz, if it works at all, thus making the computer oper-

ate slower than what it could. In their documentation, most motherboard manufacturers list

which type(s) of memory they support as well as its maximum speeds and required pairings.

The memory slots on a motherboard are designed for particular module form factors or

styles. In case you run across the older terms, dual inline package (DIP), single inline memory

module (SIMM), and single inline pin package (SIPP) are obsolete memory packages. The

most popular form factors for primary memory modules today are:

DIMM

ßN

RIMM

ßN

SODIMM

ßN

MicroDIMM

ßN

Note also that the various CPUs on the market tend to support only one form of physical

memory packaging. For example, the Intel Pentium 4 class of processors is always going to

be paired with DIMMs, while certain early Intel Xeon processors mated only with RIMMs.

So, in addition to coordinating the speed of the components, their form factor is an issue

that must be addressed as well.

DIMM

One type of memory package is known as a DIMM. As mentioned earlier in this chapter,

DIMM stands for dual inline memory module. DIMMs are 64-bit memory modules that are

used as a package for the SDRAM family: SDR, DDR, DDR2, and DDR3. The term dual

refers to the fact that, unlike their SIMM predecessors, DIMMs differentiate the function-

ality of the pins on one side of the module from the corresponding pins on the other side.

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