Ram

RAM
Introduction:
RAM stands for "random access memory" and is volatile.
When an application is launched, it is placed in RAM for
faster access by the CPU. It is one of the main
components that affects system performance. Over the
years a variety of memory types have emerged including
DIP, SIP, SIMM, DIMM and most recently RIMM.
Types of RAM:
 Static RAM (SRAM) - SRAM doesn’t have to be constantly refreshed. Uses a lot
of power. Used in old IBM XT machines and was limited to 256K per chip. This
type of memory is no longer used and has been replaced by DRAM.
 Dynamic RAM (DRAM) - DRAM uses capacitors instead of transistors and
switches. Needs constant refreshing. This type of memory is still in use, however,
has undergone upgrades such as the SDRAM and RDRAM varieties below.
 Synchronous DRAM (SDRAM) - SDRAM is tied to the system clock which
provides support for the faster bus speeds of modern computers. The speed of the
memory that you install in a system must match or exceed the system speed in
order to work. Installing RAM that is faster than the system speed will operate at
the system speed. For example, if you put PC 133 RAM into a system that is
running at 100 MHZ, the RAM would operate at the 100 MHz speed. You can
sometimes mix speed ratings when installing multiple modules, however, it is not
recommended because it can cause the system to lock up or not start at all.
 Rambus DRAM (RDRAM) - RDRAM added support for even faster bus speeds
and first surfaced around the time of the Pentium IV. RDRAM used RIMMS
which required a heat spreader to be attached to the RIMM to deal with its
increased heat levels. Unused slots on a RDRAM motherboard had to be
terminated with a CRIMM in order to function. Due to the higher cost and the
licensing fees that manufacturers had to pay to Rambus, RDRAM never took off.
 Double Data Rate Synchronous DRAM (DDR SDRAM) - With the failure of
RDRAM and increasing bus speeds, manufacturers still needed an upgrade to
regular SDRAM and DDR SDRAM was born. Like RDRAM, DDR SDRAM
increases performance by supporting 2 processes per clock cycle. DDR SDRAM
utilizes 184 pin DIMMS for desktops and either 200 pin SO DIMMS or 172 pin
micro-DIMMS for laptops. The naming convention for this type of memory is
PCxxxx. It is calculated by taking the clock speed, doubling it (double data rate),
and multiply it by 8 (the number of RAM chips on a stick). So if a module has a
200 MHz clock speed, the name would be PC3200. Like RDRAM, you must have
2 identical sticks of RAM installed as a pair. Unused slots do not need terminating
though. Recently, DDR2 SDRAM was created. DDR2 clock doubles the
input/output circuits on the chips, but does not actually increase the core speed of
the RAM.
 Windows RAM (WRAM) - Specifically designed to speed up graphical windows
operations.
 Video RAM (VRAM) - Uses a dual port access system to speed up video
operations.
Physical Types:
Type Pins
SIMMS 30/72 pins
DIMMS 168/184/240 pins
micro-DIMMS 68/144/172 pins
SO DIMMS 72/144/200 pins
RIMMS 184 pins
Important Terms:
 Double-sided RAM - RAM comes in single-sided (most common) and double-
sided varieties. Single-sided has chips on only one side, while double-sided has
chips on both sides. The motherboard must support double-sided RAM in order
for it to work.
 Parity RAM - RAM occasionally "misfires" and makes mistakes. For home users
this isn't a big deal, but for mission critical applications it can be. Parity checking
adds an extra bit to the data that the MCC uses for error detection. Parity RAM is
unable to correct the errors and doesn't always catch them.
 Error Correction Code RAM (ECC) - ECC RAM is a high-end type of memory
that detects and corrects RAM errors. Due to the expense, this type of RAM is
rare and only used in mission critical situations. The motherboard must support
ECC in order for it to work.
Installing RAM:
Installing RAM is easy. The hardest part is
making sure that you have the right kind and you
should always check the motherboard manual for
the specs. You should also try not to mix
manufacturers, speeds, or capacity when buying
multiple sticks or upgrading existing RAM.
While it will most likely work, it is better not to
do this in order to avoid problems.
Once you have the right kind, intalling the

memory stick is as simple as placing it in the slot
on the motherboard. Make sure that you handle it
from the top and avoid touching the contacts.
You may have to push with some force to get it in and to get the tabs on either end of the
slot (see image) to lock onto the notches in the ends of the stick, but don't push so hard
that you damage the memory or the motherboard. If a memory stick is not going in, make
sure it is the right kind - they are keyed so that only the right type of RAM will fit in the
slot. In the image to the right, you can see a notch in the middle of the slot - this is the
key. Once your RAM is installed, you can boot the computer and watch for the RAM
count during startup to make sure that it is being recognized properly. If you miss that,
you can always go into the Device Manager in Windows to see how much RAM the
system sees.
Virtual Memory:
Protected Mode became available with the 80286 and provided the ability to use Virtual
Memory. Virtual Memory is the ability for the computer to use free hard drive space as
extra memory. Excessive paging of the hard drive is usually a sign that the system needs
more RAM.

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Once you have the right kind, intalling the

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