A+ Certification Guide
Chapter 5
Random Access Memory
Chapter 5
Objectives

RAM Basics:
– Describe what RAM does, how it works, and how it relates to the system.

RAM Types:
– Describe types of RAM available, including SDRAM, DDR, and Rambus.

Operational Characteristics:
– Describe the features of memory modules and types of memory like ECC,
EDO, registered, and unbuffered.

Installing Memory Modules:
– Demonstrate how to install SIMMs and DIMMs properly.

Troubleshooting Memory:
– Describe issues with RAM due to incompatible memory speeds and
types.

Preventative Maintenance for Memory:
– Describe measures to take to keep memory modules clean and protected.
Random Access Memory


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Random access:
–
Means that memory addresses are dynamically allocated.
–
Different from ROM in which memory addresses are
pre-assigned to specifically coded functions.
What role does RAM play?
–
Provides CPU with data to process:
• Keyboard entries are sent to RAM addresses.
• Hard drive programs are sent to RAM addresses.
• Network data (web pages) are sent to RAM addresses.
RAM is faster than other storage, such as hard drives and USB
memory.
Installing more RAM is often the easiest way to improve system
performance without investing in a new system.
RAM Specifications to Know
(Before You Buy)


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Module type:
–
Number of pins (240,184, and 168) and placement
–
Number of RAM slots available for modules
Chip type:
–
SDRAM, DDR, RDRAM
Speed:
–
Needs to match up as multiple of motherboard front-side bus
speed
–
Measured in nanoseconds or in throughput.
Error checking:
–
Optional, purchased with database servers
Number of modules needed per bank
Dual channel or triple channel configuration
RAM Types

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

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SRAM = Static Random Access Memory:
–
Also known as L1, L2, and L3 cache memory
–
Does not require a memory refresh
–
Used with CPU to store frequently accessed data routines
–
Fast but expensive
–
Not generally upgradeable
SDRAM = Synchronous Dynamic Random Access Memory
DDR = Double Data Rate
DDR2 = Double Data Rate (enhanced)
Rambus
RAM Types Illustrated
RAM Types




(Continued)
SDRAM = Synchronous Dynamic Random Access Memory:
–
PCs made before 2000 commonly use this.
–
Rated by bus speed:
• 266Mhz bus uses PC266 SDRAM.
DDR = Double Data Rate SDRAM:
–
Rated by throughput speed in MBps.
–
PC2700 means it can deliver 2,700MBps.
DDR2 = Double Data Rate SDRAM (next-generation DDR):
–
Twice the speed of DDR.
–
PC2 prefix number designates a module as DDR2.
Rambus (RDRAM) and RIMM:
–
Not in common use.
Know These Before Taking Exam
RAM Type
Pins
Common Type and
Speed
Defining Characteristic
SDRAM
168
PC133 = 133Mhz
This original version of SDRAM is
rarely used on new computers and
has given way to DDR.
DDR
184
PC3200 = 400MHz/
3200MB/s
Double the transfers per clock cycle
compared to regular SDRAM.
DDR2
240
DDR2-800 (PC26400) = 800MHz/
6400MB/s
External data bus speed (I/O bus
clock) is 2 x DDR SDRAM.
Rambus
184 and 232
PC800 = 1600MB/s
Not used in new computers, but you
still might see existing systems using
RAMBUS memory modules.
Operational Characteristics

Memory modules are classified in various ways:
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–
–
–
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The amount of memory (in bits) found on the module
The differences between parity and nonparity memory
The differences between ECC and non-ECC memory
The differences between registered and unbuffered memory
The differences between single-sided and double-sided
memory
The following slides deal with these operational characteristics.
Memory Module Characteristics
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Single Inline Memory Module (SIMM):
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Single row of 30- or 72-edge connectors. Single refers to both
sides of the module having the same pinout.
Single Inline Pin Package (SIPP):
–
Variation on the 30-pin SIMM.
Dual Inline Memory Module (DIMM):
–
168-pin, 184-pin, and 240-pin versions. Dual refers to each
side of the module having a different pinout.
Small Outline DIMM (SODIMM):
–
A compact version of the standard DIMM module, for use in
notebook computers.
Rambus RDRAM Module or RIMM
–
A memory module using Direct Rambus memory (RDRAM)
chips.
Operational Characteristics
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Memory module width:
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8 bits = 1 byte.
–
Memory is sold as measured in bytes:
• Megabyte
• Gigabyte
–
Memory width refers to the 32-bit or 64-bit path:
• Usually matches processor/motherboard path.
A memory module is the same as a memory “bank”:
–
A bank of memory is one module installed in a single memory
slot.
–
Slots must be compatible with memory module:
• 72-pin slot versus 168- or 184-pin slot.
–
Multiple banks usually require matched pairs of memory
modules.
Operational Characteristics
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Parity and nonparity memory:
–
Error checking memory costs more.
–
Small performance decrease.
–
Two types:
• Parity checking:
– Use of a parity bit to compute a value that must match
another value to validate a data set
• ECC (error-correcting code):
– Memory that both finds and corrects errors
– Typically employed on servers
Registered versus unbuffered:
–
Buffered memory (registered):
• Enables system stability when large memory banks are
used
Installing Memory Modules
Preinstall precaution: Importance of ESD protection:
–
Memory can be damaged, and the damage may not show up for
weeks.
–
ESD strap must be attached to a ground or bare metal portion of the
chassis.
–
Hold memory modules by the side edges without touching either the
pins or the memory chips.
1.
Check to see if the locking tabs are swiveled out to open position.
2.
Line up module to accommodate the “notch” that ensures that the
module is being inserted in the right direction.
3.
Push module straight down into position:
–
A slight rocking motion from end to end helps seat stubborn
modules into the slot.
–
Engaging the locks requires extra firmness to force the locks to
close into the notches on the sides of the module.
Installing Memory

Channel A (Blue) should be installed (in pairs) before Channel B
slots are used.
Installing Memory
Troubleshooting Memory
Sources of problems:
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Incompatible module.
Overclocking/overheating.
Incompatible metals in slots and on pins:
–
Causes corrosion.
–
Need to be cleaned periodically.
Mismatched RAM speeds:
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Measured in nanoseconds.
–
Lower numbers mean faster access times.
–
Newer systems generally adjust to slowest module.
Determining if Cache RAM Has a
Memory Problem
Cache RAM holds a copy of the information in main memory.
Errors in cache RAM can appear to be errors in system RAM.
Procedure to determine if cache RAM is the cause of a memory problem:

Disable L2 cache first.
–
If the memory problem goes away, determine where L2 cache is
located (processor or motherboard).
–
If the motherboard uses removable cache module, replace it.
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If the motherboard uses nonremovable cache chips, replace the
motherboard.
–
If L2 cache is built in to the processor, replace the processor.
•
If the system runs normally, the replacement is successful.
–
If the problem persists after replacing the component containing
cache RAM, return the original component(s) to the system.

Disable L1 cache.
–
If the system runs normally, replace the CPU and retest.
–
If system runs normally after replacement, the L1 cache was faulty.
Troubleshooting Memory
RAM-Sizing Errors at Bootup
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Note the memory count reached onscreen when the memory error
is detected.
Check the motherboard documentation to see which modules
must be installed first.
Change one module at a time, starting with the one you think is
defective, until the error goes away.
Disable cache RAM in the BIOS setup when testing memory.
Preventative Maintenance for
Memory
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Keep the surfaces of the modules clean:
–
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Use compressed air or a data-rated vacuum cleaner to remove
dust.
Use the recommended voltage level for the memory
installed if your system's BIOS setup permits voltage
adjustments.
Install additional case fans over or behind the location
of memory modules to pull hot air out of the system.
Keep air intake vents in the front of the system clean.
Replace any defective cooling fans.
What Have You Learned?
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–
–
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What kind of memory would be useful to verify data
integrity?
How many memory modules are required for a CPU
with a 64-bit bus width?
What kind of memory module is typically used in
L1/L2 cache and does not require a constant
refresh?
In what speed standard is memory measured?
Chapter 5
Summary
– Describe what RAM does, how it works, and how it relates to
the system.
– Describe types of RAM available, including SDRAM, DDR,
and Rambus.
– Describe the features of memory modules and types of
memory like ECC, EDO, registered, and unbuffered.
– Demonstrate how to install SIMMs and DIMMs properly.
– Describe issues with RAM due to incompatible memory
speeds and types.
– Describe measures to take to keep memory modules clean
and protected.
Next Lesson: Chapter 6