Some people like to know a lot about the computer systems they own - or are considering buying - just because. They're like that. It's what makes them tick. Some people never find out about their systems and like it that way. Still other people - most of us, in fact - find out about their systems when they have to - when something goes wrong, or when they want to upgrade it. It's important to note that making a choice about a computer system - and its memory features - will affect the experience and satisfaction you derive from the system. This chapter is here to make you smarter about memory so that you can get more out of the system you're purchasing or upgrading.
MODULE FORM FACTORS
The easiest way to categorize memory is by form factor. The form factor of any memory module describes its size and pin configuration. Most computer systems have memory sockets that can accept only one form factor. Some computer systems are designed with more than one type of memory socket, allowing a choice between two or more form factors. Such designs are usually a result of transitional periods in the industry when it's not clear which form factors will gain predominance or be more available.
SIMMS
The term SIMM stands for Single In-Line Memory Module. With SIMMs, memory chips are soldered onto a modular printed circuit board (PCB), which inserts into a socket on the system board.
The first SIMMs transferred 8 bits of data at a time. Later, as CPUs began to read data in 32-bit chunks, a wider SIMM was developed, which could supply 32 bits of data at a time. The easiest way to differentiate between these two different kinds of SIMMs was by the number of pins, or connectors. The earlier modules had 30 pins and the later modules had 72 pins. Thus, they became commonly referred to as 30-pin SIMMs and 72-pin SIMMs.
Another important difference between 30-pin and 72-pin SIMMs is that 72-pin SIMMs are 3/4 of an inch (about 1.9 centimeters) longer than the 30-pin SIMMs and have a notch in the lower middle of the PCB. The graphic below compares the two types of SIMMs and indicates their data widths.
4-1/4" 72-Pin SIMM
3-1/2" 30-Pin SIMM
Comparison of a 30-pin and a 72-pin SIMM
DIMMS
Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.
DIMMs come in various form factors and are specific to different DRAM technologies.
168-pin DIMM: EDO and PC66/100/133 SDRAM
184-pin DIMM: DDR 200/266/333/400 DDR SDRAM
240-pin DIMM: DDR2 400/533/667/800 DDR-2 SDRAM
DIMMs transfer 64 bits of data at a time and are typically used in computer configurations that support a 64-bit or wider memory bus. Some of the physical differences between DIMMs and 72-pin SIMMs include: the length of module, the number of notches on the module, and the way the module installs in the socket. Another difference is that many 72-pin SIMMs install at a slight angle, whereas DIMMs install straight into the memory socket and remain completely vertical in relation to the system motherboard. The illustration below compares a 168-pin DIMM to a 72-pin SIMM.
4-1/4" 72-Pin SIMM
5-1/4" 168-Pin DIMM
Comparison of a 72-pin SIMM and a 168-pin DIMM.
SO DIMMs
A type of memory commonly used in notebook computers is called SO DIMM or Small Outline DIMM. The principal difference between a SO DIMM and a DIMM is that the SO DIMM, because it is intended for use in notebook computers, is significantly smaller than the standard DIMM. The 72-pin SO DIMM is 32 bits wide and the 144-pin SO DIMM is 64 bits wide. 144-pin and 200-pin modules are the most common SO DIMMs today.
2.35" 72-pin SO DIMM
2.66" 144-Pin SO DIMM Comparison of a 72-pin SO DIMM and a 144-pin SO DIMM.
MicroDIMM (Micro Dual In-Line Memory Module)
Smaller than an SO DIMM, MicroDIMMs are primarily used in sub-notebook computers. MicroDIMMs are available in 144-pin SDRAM, 172-pin DDR and 214-pin DDR2.
RIMMS AND SO-RIMMS
RIMM is the trademarked name for a Direct Rambus memory module. RIMMs look similar to DIMMs, but have a different pin count. RIMMs transfer data in 16-bit chunks. The faster access and transfer speed generates more heat. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating.
A 184-pin Direct Rambus RIMM shown with heat spreaders pulled away.
An SO-RIMM looks similar to an SO DIMM, but it uses Rambus technology.
A 160-pin SO-RIMM module.
No comments:
Post a Comment