Memory
Type: by Module Form Factors
The form factor of any memory module describes its size and pin configuration.
In a way, it is classifies memory by its physical characteristic, although not completely.
SIMMS
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.
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.
168-pin 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 168-pin 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 168-pin DIMMs install straight into the memory
socket and remain completely vertical in relation to the system motherboard.
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.
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. 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.
FLASH MEMORY
Flash memory is a solid-state, non-volatile,
rewritable memory that functions like RAM and a hard disk drive combined.
Flash memory stores bits of electronic data in memory cells, just like DRAM,
but it also works like a hard-disk drive in that when the power is turned
off, the data remains in memory. Because of its high speed, durability, and
low voltage requirements, flash memory is ideal for use in many applications
- such as digital cameras, cell phones, printers, handheld computers, pagers,
and audio recorders.
PC CARD AND CREDIT
CARD MEMORY
Memory devices used in notebook computers are packaged in modules that looked
like credit cards. Because of its compact form factor, credit card memory
was ideal for notebook applications where space is limited.
NEXT STOP: Memory: read/write memory
