| Computer Memory - Our human brain contains a large
number of memories or instructions we received from many sources such as
school, work, life experiences, etc. When information is received from one
or more of our senses, we react based our memories.
The computers memory functions
much the same as your own brain. The CPU along with this internal memory,
makes up the computer's "brain."
MEMORY is a term that is used
to represent storage that has "almost" instantaneous access by the CPU or
other processor. Every computer will have some type of
memory. However, the memory we speak of the most often is Random
Access Memory (RAM).
RAM is the primary memory used
when we "boot" (start up) a computer. During boot-up the PC's operating
system and device drivers are loaded into RAM.
RAM has many functions, but
its primary function is to store programs and drivers for the various
system devices. It is probably the most important type of memory in your
PC.
Each time we start up the
computer, memory is filled with instructions to give it in ability to do
work. You control which instructions will go into the computer's
brain by loading or starting software programs.
Once a program is in memory, the computer will evaluate inputs from
many devices and react accordingly. The type of instructions that can be
placed in memory are:
- How to print a letter or
document to a printer.
- How to calculate the answer
to a math problem.
- How to send information
over a telephone line to another computer.
Each time you
start another program you empty the computer's brain and install a
different set of instructions, thus giving the computer a different
ability. The most typical input is commands you type on the
keyboard.
 When you enter a command from your
keyboard, the CPU (microprocessor) processes the command and calls for
data (a program or data file) to be copied from a storage device (hard
disk, floppy, CD-ROM, etc.) into memory, where it is stored temporarily
until the CPU needs it.
The memory then provides the
data to the CPU more quickly than from the storage device. This data may
be a program or actual data such as a letter you previously typed.
"RAM" is what you are referring to when you say "my system has 8, 16, 32
MB of memory".
Memory Types - Your personal PC may contain several different types, each with a
different purpose.
Some of the terms you will hear concerning memory are: RAM, DRAM,
SRAM, EDO RAM, SDRAM, ROM, PROM, EPROM, EEPROM, FLASH, internal and
external cache, etc. In this tutorial we will cover the three basic
types of memory found in a computer:
- RAM - Random Access
Memory.
- ROM - Read Only Memory.
- Cache - A fast storage type of
memory.
Before
we confuse you more, let us give you a table which will list these types
and more, and the normal uses for them:
| Memory Type |
How it is
Used |
| ROM |
Read only Memory used
for BIOS chips, CMOS chips, and Special function
Chips. |
| RAM |
Main Memory - FPM RAM,
EDO & BEDO RAM, Synchronous DRAM (SDRAM) |
| DRAM |
Actual memory chips on
SIMM boards or Motherboard (Main Memory)-DRAM is actually FPM, EDO
RAM, or SDRAM on a chip. |
| SRAM |
Static RAM, used as
External (L2)CACHE. L2 SRAM is on chips. L2 On-board cache is in the
CPU chip. It comes in 3 basic types - Async SRAM, Sync SRAM, and PB
SRAM (Pipelined Burst RAM - the fastest). |
| FPM
|
Some modern computers
today use Fast Page Mode DRAM. The difference between FPM DRAM and
regular DRAM is in the way the memory is accessed by the controller.
When data needed is in the same page or row that the previous data
was found, The controller only has to indicate the next column
location to access the data. By not having to generate a complete
address the memory is accessed a little faster. |
| EDO
RAM |
Extended Data Out RAM
Memory used on Pentium or later type motherboards. EDO RAM is not
designed for 486 or earlier motherboards. EDO RAM is on 72-pin
SIMMs. EDO RAM comes in plain EDO and Burst EDO (BEDO RAM) versions.
EDO and BEDO RAM are ok in systems with bus speeds up to
66MHz. |
| SDRAM
|
Synchronous DRAM
(Pentium w/MMX has SDRAM as main memory). SDRAM memory is on 168-pin
DIMM chips. SDRAM comes in several types with speeds from 10, 15,
20, and 25 nanoseconds. |
| FLASH |
Normally, it is memory
on a card. The size of a PCMCIA card. |
| Cache Memory |
Normally, it is memory
on a card. The size of a PCMCIA
card. |
How Much RAM Memory Do You
Need?
No one can
say exactly - you need to know things about your system operating system,
the type of applications you will run on your PC (graphics, multi-media,
word processing, etc). To give you an idea of what we are talking about,
refer to the chart below.
| Quantity |
General Uses |
| 4 MB
|
DOS applications, maybe
Windows 3.1, a few old word processing packages, etc. |
| 8-12
MB |
Windows for Workgroups,
small word-processing, E-Mail, only a few (1 to 3) applications
open. Maybe an Internet package such as Internet Explorer or
Netscape, AOL, etc. Will be somewhat inefficient. |
| 12-16
MB |
Windows for Workgroups,
supposedly Windows 95 (not really!), Word processing, E-Mail, WEB
interfaces, FAX, spreadsheets, and low level graphics applications.
Few applications open simultaneously. |
| 16-24
MB |
You can now load
Windows NT Server, Windows NT Workstation, and Windows 95. NT Server
works inefficiently at this level. Some number crunching,
spreadsheets, E-Mail, WEB browsers, some graphics and audio-visual
(but weak). |
| 24-32
MB |
Now you can do heavy
applications. Spread sheets, statistical analysis programs, large
databases, and multiple applications open. Even a little graphics
and games - a an acceptable speed. |
| 32-64
MB |
Starting into decent
graphics, with word processing, page layouts, even some good "audio
visual" type applications. |
| 64-128 |
You are now ready for
medium to high level graphics and animation - if you have the other
necessary hardware. Photo editing, multimedia, word processing,
illustration graphics, the whole nine yards! |
| 128+
MB |
Now you are talking!
This is the level for efficient Windows NT Servers with many users.
Multimedia and about everything
else! |
Just remember this: You can have all the RAM memory you can install;
but, if you do not have adequate internal and external cache, good video
cards, a 32-bit or 64-bit bus, etc., you will still operate somewhat
slower.
Purchasing
Memory
What do you need to know before purchasing memory?
One of the first things
you need to do is determine if you need more memory and why. Ask yourself
the following questions.
- Am I getting messages from applications (especially Windows
applications) indicating there is not enough memory to run applications,
save files, etc.?
- Are your applications which run graphics, games, spreadsheets, etc.
performing at a slow rate?
- Is your hard drive light flashing when running programs and you are
not saving files at the time?
If the answer is yes to any of the above then you probably need
more memory in your system.
the next step is to consult the
technical manual that came with your computer.
Most manuals, whether on-line or physical, will tell you exactly what
type of memory your system supports.
If there is a
specific way in which memory must be configured, the manual should tell
you. If you can not get information in this way, contact the
manufacturer's help desk.
When you boot your PC, you
usually see a display of memory which shows Conventional and Extended
memory.
The combination of extended, conventional, and upper memory usually
will add up to the total number of memory you have installed on your
PC.
There are several questions
you need to ask before purchasing memory:
- What type of memory can my PC accept?
- 30 pin SIMM, parity or non parity?
- 72 pin SIMM, parity or non parity?
- 168 pin DIMMs?
- How much memory do I have?
- What is the speed of DRAM memory my PC accepts (in nanosecond
speed)?
- Do I have open memory slots on my motherboard? (if not, you will
probably have to get larger capacity SIMMs such as a 32MB SIMM rather
than multiple 16 MB SIMMS.
- How much memory will my PC accept? Am I "max'd out"? Some machines
such as a EDS 386 only had 8 slots for SIMM chips, for a max of 32MB
of memory.
The next step is finding a source to purchase from. One
of the best sources is http://www.pricewatch.com/
For a complete discussion of all types of memory, I suggest you go
to http://www.kingston.com/ or http://www.centon.com/on the WEB.
 
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