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What
is RAM and what does it do?

RAM
- Random Access Memory, or volatile memory, is used by the system
to store data for processing by a computer's central processing
unit (CPU), also known as the processor. The processors used in
most PCs are made by Intel, AMD, IBM/Cyrix, and VIA/Cyrix.
VIA
has purchased Cyrix, and has issued small, cheap, integrated PC-in-a
box units that can access the Internet.
RAM
stores the data in memory cells that are arranged in grids much
like the cells are arranged in a spreadsheet, from which data,
in the binary form of 1's and 0's, can be accessed and transferred
at random to the processor for processing by the system's software.
The
data stored in a hard disk drive (HDD) cannot be accessed at random.
Whole sectors, containing blocks of data, are transferred from
a hard disk drive, placed in a large swap file on the same drive,
and only then are selected files transferred to RAM for random
access by the processor, which is itself only performing the instructions
of the system's operating system (usually Windows), and its application
software.
When
the computer is turned off, all of the data in the RAM memory
is lost, hence its alternative name of volatile memory, whereas
all of the data on a hard disk drive is retained permanently until
it is intentionally erased.
The
motherboard (or mainboard) manual (that should be
provided with a new or a second-hand PC) will provide all of the
details about the different types of supported RAM, and the various
combinations of modules per bank for each type that can be successfully
installed.
There
are many flavours of RAM - with or without error checking (ECC),
buffered or unbuffered, etc., but at the moment, two main types
of RAM in DIMM modules are available - standard and double
density modules. The module can be single-sided (with memory
chips on one side of the module only) or double-sided (with memory
chips on both sides of the module)..
Not
all motherboards can use the double density type, and so will
only be able to read the chips on one side if you install double-sided
modules (a 256MB module will typically only register as 128MB
with Windows), so always make sure that the RAM you are buying
as an upgrade is compatible with the motherboard. It is always
a sure sign that the motherboard does not support the type of
RAM installed if it is not all recognised by the system.
Note
that the amount of RAM is actively counted when the system boots
(visit the BIOS page on this site to see images of start-up screens
showing the memory count), and is reported in the Windows Device
Manager, or by entering msinfo32 in the Start =>
Run box.
ECC
stands for Error-Correcting Code. It is error correction
hard-coded into the RAM chips themselves. This type of RAM is more
expensive than other types, and is mainly used in mission-critical
systems.You can install it in a system if it is supported by the
motherboard.
Registered
or buffered RAM has a built-in buffer that stores the data before
it is transferred to the hardware memory controller. It increases
the reliability of the RAM enormously. Even so, most of the RAM
used in personal computers is unbuffered, and works reliably enough
in that role.
How
to install RAM
Installing
the DIMM modules (that have been used in all new computers for
several years) is merely a matter of pushing the module directly
down into the DIMM slot as shown in the diagram below. Note
that the notche(s) along the connector edge of the module must
match the divisions in the slot.
Depending
on its architecture, there will always be at least one notch in
a RAM module, but never more than two. The SDRAM module below
has two notches, but a DDR DIMM module (below that) will only
have one, and a RIMM module (used only in motherboards designed
for Pentium 4 processors) has two closely-spaced notches.



Note
that you should consult the motherboard's manual to find out if
the slots have to be filled in an order of rank. Some motherboards
require that Bank 0 be filled first, followed by Bank 1 and 2,
etc., while some motherboards allow any bank to be filled.
Systems
using certain BIOS versions and 768MB or more of RAM suffer a
marked slow-down
Certain
versions of the Award
(now owned by Pheonix)
BIOS installed by many motherboard manufacturers slow down the
computers that use them very markedly when more than 768MB of
RAM is installed. This problem affects BIOS versions prior to
number 1004, so, if you have not done so, and you have
or want to install 768MB or more of RAM, download and install
the latest BIOS, currently at number 1011, from the PC/motherboard
manufacturer's site.
Too
much RAM can cause problems with some versions of Windows
Note
that if you are upgrading your RAM memory, a computer using Windows
95 or Windows 98 (first edition) will not recognise more than
256MB. Moreover RAM that Windows cannot cache (recognise) will
be accessed as slowly as the virtual memory swap file (win386.swp)
that Windows creates on the boot hard disk drive to use when the
amount of RAM runs out. Therefore, adding too much RAM can slow
down a system considerably. Unless you are using a non_Windows
operating system such as Linux, and unless you employ the fix
a link to which is provided below, your must have Windows 98SE
or run a later version to use more than 256MB of RAM.
This
limitation does not apply to Windows 2000 and Windows XP.
Moreover,
it has now become known the Windows 98 SE (second edition) has
trouble with 512MB of RAM and more. Windows 9.x systems were not
designed to use large amounts or RAM. Most home users of Windows
9.x are unlikely to require this much RAM in any case, so, if
possible, it is advisable to install less than 512MB. If you need
to use more, use Windows 2000, or Windows XP, both of which are
based on the Windows NT architecture. Windows 95, 98, and Me are
based on Windows 95 architecture.
If
you have more than 512MB of RAM installed and this causes any
problems, you can restrict the amount of RAM used to 512MB (or
any other amount) by entering msconfig in the Start => Run
box, clicking the Advanced button, and enter the appropriate restriction
in the Limit memory to... box - and enable it with a check mark.
There
is a configuration file fix that can be applied to make Windows
98 function with as much RAM as you are likely to throw at it.
See this excellent article - Windows 98 & WinME Memory Management
-
http://aumha.org/a/memmgmt.htm
You
can also read more about this in a Knowledge Base (KB)
article Q253912 at Microsoft's site -
http://support.microsoft.com/support/kb/articles/Q253/9/12.asp
Microsoft
has a tendency to change the links to KB articles, so if a link
fails to work enter the article's Q number in the search
box on the following page. As you can determine from the information
in the link itself, the Microsoft link above leads to the article
with the Q number of Q253912.
http://support.microsoft.com/default.aspx?pr=kbinfo&
Memory-card
readers
If you
use several different kinds of devices that use their own kinds
of memory cards, you can purchase memory-card readers that can
read the different cards.
For instance,
an MP3 player uses MMC cards, a Personal Digital Assistant (PDA)
uses Compact Flash cards, and a Sony Vaio notebook computer uses
it own Memory Stick cards.
You could
spend a long time transferring files from the devices to a desktop
computer by using, say, USB cables. But if you buy an inexpensive
memory-card reader, you can eliminate the need to plug and unplug
lots of different USB cables.
The 6-in-1
Media Reader requires a 3.5" drive bay of the kind that
houses a floppy disk drive. It reads Multimedia Cards (MMC), Secure
Digital (SD), Memory Stick, PC Card (PCMCIA), Compact Flash, and
SmartMedia card formats. You can copy the contents of one type
of card to the desktop computer's hard drive, insert a different
card, and copy the contents to it, or you can just copy the contents
to the hard drive.
You can
buy the 6-in-1 Media Reader from http://www.simply.co.uk/.
The USB
2.0 6-in-1 Flash Reader, is an external USB device that
can be connected to either a notebook or desktop computer. It
also has a USB 1.1 port that enables you to connect a printer
or scanner to it.
You can
buy a 6-in-1 Flash Reader from http://www.watford.co.uk/.
Motherboard
and BIOS settings
The
motherboard's manual will also provide you with any jumper settings
that might be used to set the RAM's speed - for 66MHz EDO RAM,
PC 100 SDRAM at 100MHz, PC 133 SDRAM at 133MHz, etc. - and the
BIOS settings that might set the speed instead of motherboard
jumpers, as well as set other optional settings such as the bank
interleave and timing settings.
For
images of and information on the jumpers and DIP switches
used on motherboards to enable various functions, visit the Motherboard
page of this site.
You
can also visit this page of the PC Guide - http://www.pcguide.com/ref/mbsys/cache/char_Cacheability.htm
to read an article on RAM cacheability. There are also
several other pages devoted to RAM on this site.
Visit
this site for a guide called How
to Install Memory in Your PC.
And
visit http://www.geocities.com/budallen98_98/dennis.html
and search for the article called How Much RAM Will Windows
98 "USE".
Unfortunately,
the ability of Windows to use RAM does not always coincide with
ability of a motherboard's chipset to cache RAM, so be
sure to check your motherboard's manual before you upgrade. The
motherboard's chipset determines how much RAM can be cached. If
the motherboard has an elderly chipset, the amount of RAM it can
cache might be limited to as little as 64MB.
If
a motherboard can only cache 64MB of RAM, such as one with
the elderly Intel TX chipset, and you install 128MB, even
if it works, it will slow the system down significantly, because
the excess RAM cannot be cached, and so will be accessed in the
same relatively slow manner as the virtual memory swap file that
Windows sets up on the hard disk drive is accessed.
The
moral of the story - if you have an ageing PC, always find
out how much RAM your motherboard can cache before upgrading.
Only
purchase a new computer that has at the
very least PC 133 SDRAM.
This kind of RAM is certified to run at 133MHz.
If
you are looking for a system with the fastest available RAM consider
one with DDR RAM, or the more expensive, but not necessarily
superior Rambus RAM, which
is supplied in modules called RIMMs.
If
you are buying RAM as an upgrade, purchase it from a supplier
of quality RAM such as Crucial. The Memory Selector
at the top of this page will take you to the RAM information on
Crucial's site that applies to your system.
RAM
of poor quality will isn't worth any savings you can make, because
it can be the source of all kinds of system failures.
Motherboards
that use EDO RAM supplied as SIMM modules are no
longer being made, but you can still purchase EDO RAM from suppliers
such as Crucial, or second-hand from computer auction sites.
Make
sure that the RAM installed or installable on your motherboard
is supplied as one or more DIMM (or, if your motherboard
supports it - RIMM) modules.
Unless
your motherboard can run the RAM speed and the bus speeds independently
of one another (as is the case with the FIC VA-503+ AT form-factor
motherboard), remember not to use ordinary 66MHz RAM when the
motherboard bus (FSB) is set to run at 100MHz - the newer PC100
(100MHz) SDRAM is required.
Likewise
do not use PC 100 SDRAM, which runs at 100MHz, on a 133MHz system
bus. Use PC 133 SDRAM.
DDR
SDRAM and Rambus RAM --
What is RAM and what does it do? -- Which
DDR RAM? -- How to install RAM?
-- How to identify the size
of RAM modules? -- Different types of
RAM? -- Mixing brands can often cause
problems -- Memory Frequently Asked
Questions
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