Computer Memory

System Memory

The system memory is the place where the computer holds current programs and data that are in use. The term “memory” is somewhat ambiguous; it can refer to many different parts of the PC because there are so many different kinds of memory that a PC uses. However, when used by itself, “memory” usually refers to the main system memory, which holds the instructions that the processor executes and the data that those instructions work with.

Your system memory is an important part of the main processing subsystem of the PC, tied in with the processor, cache, motherboard and chipset.

Memory plays a significant role in the following important aspects of your computer system:

Performance: The amount and type of system memory you have is an important contributing factor to overall performance. In many ways, it is more important than the   processor, because insufficient memory can cause a processor to work at 50% or even more below its performance potential.

This is an important point that is often overlooked.

Software Support: Newer programs require more memory than old ones. More memory will give you access to programs that you cannot use with a lesser amount.

Reliability and Stability: Bad memory is a leading cause of mysterious system problems. Ensuring you have high-quality memory will result in a PC that runs   smoothly and exhibits fewer problems. Also, even high-quality memory will not work well if you use the wrong kind.

Upgradability: There are many different types of memory available, and some are more universal than others. Making a wise choice can allow you to migrate your memory to a future system or continue to use it after you upgrade your motherboard.

Other thing to know about memory. What is CAS Latency?
CAS Latency (also referred to as latency) is the amount of time it takes for your memory to respond to a command. Specifically, it is the length of time between memory receiving a command to read data, and the first piece of data being output from memory. Latency is measured in terms of clock cycles and is often noted as CL2 (two clock cycles) or CL3
(three clock cycles).

What is the performance difference between CL2 and CL2.5 DDR modules?
CAS latency 2 parts process data a little quicker than CAS latency 2.5 parts in that you have to wait a half clock cycle less for the initial data. However, after the first piece of data is processed, the rest of the data is processed at equal speeds. Latency only affects the initial burst of data. Once data starts flowing, there is no effect.

Bear in mind, a clock cycle for a system properly using a PC2100 DDR module is 8 nanoseconds, so the difference between CAS latency 2 and CAS latency 2.5 for PC2100 parts is 4 billionths of a second. You probably won’t be able to notice the difference.

Types of memory related to the computer. 

DDR Memory

184-pin DIMMs are used to provide DDR SDRAM memory for desktop computers. Each184-pin DIMM provides a 64-bit data path, so they are installed singly in 64-bit systems. 184-pin DIMMs are available in PC2100 DDR SDRAM,  PC2700 DDR SDRAM or PC333 DDR SDRAM. To use DDR memory, your system motherboard must have 184-pin DIMM slots and a DDR-enabled chipset. A DDR SDRAM DIMM will not fit into a standard SDRAM DIMM socket.

The number of black components on a 184-pin DIMM may vary, but they always have 92 pins on the front and 92 pins on the back for a total of 184. 184-pin DIMMs are approximately 5.375″ long and 1.25″ high, though the heights may vary. While 184-pin DIMMs and 168-pin DIMMs are approximately the same size, 184-pin DIMMs have only one notch within the row of pins.

168-pin DIMM (dual inline memory module) 


168-pin DIMMs are commonly found in Pentium and Athlon systems. Each 168-pin DIMM provides a 64-bit data path, so they are installed singly in 64-bit systems. 168-pin DIMMs are available in FPM, EDO, 66MHz SDRAM, PC100 SDRAM, and PC133 SDRAM. When upgrading, be sure to match the memory technology that is already in your system. Information on which memory technology is used by your system is included in the Memory Selector or your manual.

RamBus Memory 232 pin

Rambus memory technology is a proprietary memory technology
invented by Rambus Inc. It was selected by Intel Corporation to power
a new generation of high-performance PCs with increasing memory
bandwidth requirements. Rambus memory modules, called RIMM™
modules, are used on PCs with Intel chipsets supporting Rambus
memory. Intel launched the new Rambus platforms in late 1999.

Rambus is considered to be a revolutionary memory technology, as
opposed to evolutionary, when compared to SDRAM because it
requires a totally new memory architecture.

RIMM modules were initially launched in speeds of 600, 700, and 800
MHz; however, today, 800 MHz RIMMs are Kingston’s most sold
RIMM modules. The RIMM modules are classified as PC600, PC700,
and PC800 corresponding to their speed (data rate), and are available
in ECC- and non-ECC versions. Rambus memory chips are called
RDRAMs (for Rambus DRAMs).

Micro-BGA RDRAM memory chips in a Kingston SO-RIMM
prior to the riveting of the heat spreader

RIMM modules also utilize a chip packaging technology called
Micro-BGA™ packaging. Micro-BGA packaging is a type of Chip
Scale Packaging (CSP) technology. An RDRAM chip consists of the
memory “die”, cut from the silicon wafer. The die is encapsulated in a
very thin package that includes its electrical connections which is an
array of solder balls (called the Ball Grid Array).

Because this CSP chip package is fragile, Kingston’s RIMM and
SO-RIMM modules are covered by an aluminum heat spreader, which
both protects and helps cool the RDRAM memory chips.