Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
Chapter 4
RAM
Learning Objectives
In this lesson, you will learn to identify various RAM types, understand how various forms of RAM
function, and learn how to install or upgrade RAM. By the end of this lesson, you should be able to do
the following:

Identify the different types of RAM packaging

Explain the varieties of DRAM

Install RAM properly

Perform basic RAM troubleshooting
Discussion Point
Electrostatic discharge Recall from the first lesson in Chapter 2, the issues concerned with
electrostatic discharge (ESD) and the precautions to be taken when handling
components. The CPU and RAM are both very susceptible to ESD damage.
Pre-test
1.
What kind of RAM packaging would you typically find in modern Pentium-type systems?
2.
What controls the dynamic random access memory (DRAM) chip?
3.
Explain DDR-DRAM.
4.
List some different RAM packages.
5.
What is the typical type of RAM found in most systems today?
Lecture Outline
Historical/Conceptual
I.
Understanding Dynamic Random Access Memory (DRAM)
A. Introduction
Copyright © 2007 by The McGraw-Hill Companies
Page 1 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
1.
Chapter 4
Special semiconductor that temporarily stores ones and zeroes in microscopic capacitors
and transistors.
2.
Refers to byte-wide memory.
3.
Visualize like a spreadsheet:
a)
A 1 MB 8 RAM stick would be represented as 8 columns wide (8 bits = 1 byte) and
1,048,576 rows deep (1 MB).
B. Organizing DRAM
1.
Intel Processors since the 8088 require chips to be stored in 8-bit (1 byte) chunks.
An exception to the 8-bit rule is when parity was used. A byte with a parity bit would require a
chip 9 bits long. However, the data is still only 8 bits long.
2.
Older chips were stored in single bits requiring eight chips to make a byte.
3.
Not easy to determine actual width or capacity based on what’s written on chips.
4.
CPU accesses memory via MCC (as described in Chapter 2).
C. Practical DRAM
1.
Early RAM on the 8088 used an 8-bit–wide data bus.
2.
Some commands were more complex, requiring 2 bytes. The codebook (instruction set)
allowed this. They CPU would recognize commands that were 2 bytes wide and simply
read both commands.
3.
8086 chip would have worked with 16-bit data bus, but Intel made a marketing decision
using the cheaper and easier to implement 8088.
For many of us, “buses” tend to run together. What’s the difference between the address bus,
the external data bus, and the frontside bus?.
1. Address bus
This is what addresses memory. Like a house has an address, memory
has an address. We can store bytes of data in different addresses. The more address lines
we have on the address bus, the more bytes of data we can store.
2. External data bus
This is where the data is passed back and forth between CPU and
memory (via the MCC).
Copyright © 2007 by The McGraw-Hill Companies
Page 2 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
3. Frontside bus
Chapter 4
With the advent of cache onboard the chip and accessed directly from the
CPU (also known as the backside bus), the external data bus is now known as the
frontside bus.
D. DRAM sticks
1. 80386 required 32-bit–wide data bus (as opposed to 8088, 8-bit-wide). If chips were still
only 1 bit wide, this would have required a minimum of 32 chips on the board.
2. DRAM manufacturers began creating wider chips ×4 (4 bits wide), ×8 (8 bits wide), etc.
3.
Single inline memory modules (SIMM) came in 30-pin and then 72-pin modules. SIMMs
inserted into special SIMM sockets.
4.
Current RAM is 32 bits wide, 64 bits wide, and sometimes 128 bits wide. The width of the
frontside bus is dictated by the MCC being used.
5.
When replacing RAM, you need to know the width of the module being replaced. This is
different from the older method of identifying the width of the individual chips.
Discussion Point
Banking
In older PCs it was important to know how wide the data bus was and how wide the memory
stick was, because the widths had to match. Let’s say the address bus was 64 bits
wide. The memory stick (or sticks) needed to be just as wide to match the 64-bit bank.
If you had 32-bit memory sticks, you would need two to fill the bank. If you had a 64-bit–
wide memory stick, one stick would be enough.
Today, most sticks are 64 bits wide and most motherboards are 64 bits wide. As 128-bits–wide
motherboards emerge on the market, the same banking principle will likely apply. You’ll
need wider sticks or you’ll need to use two sticks per bank.
Discussion Point
Identifying RAM capacity
Except for parity, it is virtually impossible to distinguish one RAM size module from another
(width or depth) by simply looking at it. Although it is sometimes possible to find
information on the Web based upon the coding you find imprinted on the chips, it is
Copyright © 2007 by The McGraw-Hill Companies
Page 3 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
best to label RAM chips when you buy them so you will always be able to distinguish
one from another.
E. Consumer RAM
1.
Even though RAM comes in packages wider than bytes, RAM is still described in bytes,
such as a 256-MB stick or a 512-MB stick.
Discussion Point
Terminology
Most PC professionals call a RAM module a “stick.” If buying RAM, you would typically ask for
a xx-pin stick with yy MB RAM where xx equates to the number of pins on the RAM
module and yy equates the amount of RAM.
Essentials
II. Types of RAM
A. Synchronous dynamic RAM (SDRAM)
1.
Synchronized with the system clock.
2.
Came on stick called a dual inline memory module (DIMM).
3.
Wide number of pins on DIMMs. 168 pins common on desktops. Laptops had 68 pins, 144
pins, 172 pin micro-DIMM. Laptops also had small outline-DIMM (SO-DIMM) of 72 pin,
144 pin, or 200 pins.
4.
Most were 64 bits wide. (72 pin SO-DIMM was 32 bits.)
5.
Instead of an access speed, it has a clock speed measured in MHz. Common speeds were
66, 75, 83, 100, and 133 MHz.
B. Rambus DRAM (RDRAM)
1.
RDRAM could support speeds on the frontside bus of up to 800 MHz. This was needed for
the quad-pumped CPUs.
2.
Originally thought to be the next best thing, RDRAM suffered delays in manufacturing and
was significantly more expensive than SDRAM.
3.
Commonly called a RIMM (though RIMM doesn’t specifically stand for anything).
Copyright © 2007 by The McGraw-Hill Companies
Page 4 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
4.
184-pin sticks for desktops. 160-pin SO-RIMM for laptops.
5.
Requires all RIMM slots (in a pair) to be populated. Continuity RIMM (CRIMM) sticks
were essentially RIMM terminators.
6.
RDRAM was proprietary and licensed to work only with Intel systems for several years.
The goal was to push AMD out of the marketplace, but the result was growth of other types
of memory and memory chips.
C. DDR SDRAM
1.
Fast RAM supported by AMD and other manufacturers.
2.
Doubles the throughput over SDRAM (makes two processes for each clock cycle).
3.
Commonly referred to as DDR, DDR RAM, and DDRAM.
4.
Comes in 184-pin DIMMs.
5.
Slots are keyed with guide notches, so you cannot insert RAM in incorrect slots.
6.
Base clock is 100 MHZ to 300 MHz with the DDR speed rating double the clock speed. To
determine the PC speed rating (bytes per second), multiply the DDR speed in MHz by 8.
For example, a chip with a clock speed of 200 and doubled DDR speed rating of 400 would
be referred to as a PC 3200 (400 MHz × 8).
7.
Supported as standard system RAM, even by Intel for the Pentium 4.
8.
Can make use of dual-channel architecture.
a)
Similar to RAMBUS in how it improves performance.
b) Works only when two slots are populated.
8.
Dual slots are often blue. If third slot exists, it is black.
D. DDR2
1.
Doubled the clock to increase buffering and overall performance.
2.
Uses 240-pin DIMM (not compatible with DDR DIMM).
3.
PC Rating determined similar to how DDR is determined (with another doubling), and
prefixed by a 2. For example, for DDR2 with a clock speed of 200 MHz, the DDR I/O
Copyright © 2007 by The McGraw-Hill Companies
Page 5 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
speed would be 400 MHz, the DDR2 speed rating would be DDR2-800, and the PC speed
rating would be PC2-6400
Discussion Point
RAM speeds
In general, it is not a good idea to mix speeds on your RAM sticks. While this practice may
sometimes work on some motherboards, it is far from predictable or consistent. The
results may vary from working fine to intermittent crashes. Sometimes you can use one
speed in one bank and another speed in another bank, but it is best not to mix speeds
in the same bank.
Although your system can use faster RAM than your motherboard needs, you will not see any
improvements over normal operations.
E. RAM variations
1.
Double-sided DIMMS
Many sticks come in single-sided versions and double-sided
versions. Some double-sided sticks can’t go into all motherboards.
2.
Latency
a)
Refers to how quickly the RAM responds to the electrical signal.
High latency High wait time. Takes longer for RAM to respond. CL3 is high latency.
b) Lower latency Lower wait time. RAM can get the signal out in fewer clock ticks.
CL2 is low latency.
c)
The goal is to match the RAM with the motherboard. If necessary, when swapping
RAM, the RAM timings can be adjusted in BIOS as discussed in Chapter 5.
2.
Parity and ECC Detect errors in memory.
a)
Parity allows the computer to detect whether an error occurred in the reading or
writing of data in memory.
b) Error correction code (ECC) is an improvement over parity. Not only can errors be
detected, but they can also be corrected.
c)
ECC is slower because of the extra calculations required.
Copyright © 2007 by The McGraw-Hill Companies
Page 6 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
d) Parity and ECC are used only on higher end systems. Often applications will check
and/or correct errors on the fly instead of depending on the hardware to do so.
2.
Buffered registered DRAM
a)
Typical motherboards have only four memory slots and can accept only four memory
sticks.
b) More than four sticks of DRAM causes electrical challenges that can be overcome
with “buffered registered DRAM.”
c)
If the motherboard accepts more than four sticks of RAM, it may require buffered
DRAM.
III. Working with RAM
A. Adding more RAM almost always improves overall system performance, processing speed, and
stability.
1.
Determine whether insufficient RAM is the cause of system problems.
2.
Pick the proper RAM for the system.
3.
Use good installation practices such as keeping RAM sticks in anti-static packaging and
following strict ESD practices.
4.
Two symptoms show need for more RAM:
a)
General system sluggishness.
b) Disk thrashing or excess hard drive accessing, generally indicates using excessive
movement of files between RAM and swap file or virtual memory space on hard drive.
B. Do you need more RAM?
1.
Is you system sluggish? Slow running system, especially with more programs running
indicates RAM may be a bottleneck.
2.
Are you experiencing disk thrashing? Disk thrashing occurs when data is swapped between
physical RAM and virtual RAM (the paging file). The symptom of disk thrashing is that
the disk drive LED is blinking feverously and you can hear it almost constantly moving.
Copyright © 2007 by The McGraw-Hill Companies
Page 7 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
Cool Tools
FreeMeter is a free utility mentioned in the text that can be downloaded from
www.tiler.com/freemeter. It provides the same information you can obtain from a
Windows tool by pressing CTRL-SHIFT-ESCAPE keys at the same time (to open Task
Manager) in many Windows operating systems. However, FreeMeter is a little clearer in
stating how much physical memory is available and being used.
1. Download and Install FreeMeter into a Windows operating system.
2. Launch FreeMeter and observe the disk activity. Excessive disk activity may be disk
thrashing due to low memory.
3. Observe physical memory information and page file information on FreeMeter. A low
percentage of available memory (less than 10%) may be an indication that memory is a
bottleneck and your system would significantly benefit from more RAM.
4. Press CTRL-SHIFT-ESCAPE to launch the Task Manager and select the Performance tab.
Note that the operating system will almost always create and use a page file, even with
a lot of RAM. Just because the page file exists doesn’t mean data will constantly be
swapped back and forth between the RAM and the hard drive.
5. Compare the Task Manager physical memory counters with the physical memory
information shown in FreeMeter.
6. Compare the Task Manager PF Usage display (page file usage) with the page file
Information in FreeMeter.
3.
System RAM recommendations. Microsoft’s system RAM recommendations for various
Windows operating systems are very low. As the old joke goes, don’t try this at home.
Instead, consider installing additional memory to reach the reasonable minimum, for solid
performance or if you are a power user.
a)
Windows 2000. Reasonable minimum: 128 MB. Solid performance: 256 MB. Power
User: 512 MB.
b) Windows XP. Reasonable minimum: 256 MB. Solid performance: 512 MB. Power
User: 1 GB.
Copyright © 2007 by The McGraw-Hill Companies
Page 8 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
c)
Chapter 4
Windows Vista. Reasonable minimum: 512 MB. Solid performance: 1 GB. Power
User: 2 GB.
4.
Determining current RAM capacity. Use Properties for My Computer to see the RAM
configuration.
C. Getting the right RAM
1.
Different types of RAM were discussed in the preceding pages. You must put the same
type of RAM into a motherboard that accepts it. The first step is to determine what the
motherboard will accept. You will typically check the manual for this answer.
2.
Open the case and see what’s installed. Make certain the power is off. For example, if you
system can accept 2 GB and the tools tell you that you have 1 GB installed, you might
jump to the conclusion that you can add 1 GB more. However, opening the case might
show you that you have four 256-MB sticks. There’s no room for new RAM unless you
replace the existing RAM.
3.
Mix and match at your peril. Different RAM sizes aren’t always handled well in
motherboards. It’s best to choose RAM sticks that match technology, capacity, and speed.
4) Mixing speeds
a)
Its best not to mix speeds.
b) Worst case, you may cause random lockups and data corruption.
c)
Best case, it’ll work at the slowest speed.
d) You can place higher rated RAM into a slower rated motherboard. The RAM will
work at the slower rate of the motherboard.
Cool Tools
CPU-Z was introduced in Chapter 3, “Microprocessors.” It’s also quite useful here. Pulling the
RAM out is an ESD risk, and even then the numbers on the sticks don’t always tell what
kind of memory you have. Now use CPU-Z.
1. Launch CPU-Z.
Copyright © 2007 by The McGraw-Hill Companies
Page 9 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
2. Select the Memory tab and observe both the Type and Size of your memory. Observe the
CAS# Latency.
3. Select the SPD tab (SPD stands for Serial Presence Detect). Notice that in Memory Slot
Selection, you can select any of the slots.
4. Select Slot 1 and observe the Module size, the Max Bandwidth.
5. If it exists, select Slot 2 and observe the Module size, the Max Bandwidth.
D. Installing DIMMs and RIMMs
1. The sticks are keyed so they can go in only one way.
2. Line up the keys and place the stick in the slot.
3. Push down and the tabs will lock into position.
4. SPD ( Serial Presence Detect). Upon power-up, the SPD chip detects the memory in the
system and reports it to the BIOS.
a)
Any program can query the SPD. CPU-Z, a Cool Tool, displays some of the SPD
information.
5. The RAM count.
a) Upon power-up, BIOS will count and report the amount of RAM detected.
b) This is often a binary count, so 256 MB wouldn’t be exactly 256 million.
c) Usually a ballpark number tells you you’ve been successful.
E. Installing SO-DIMMs on laptops
6. For years, laptops had proprietary RAM packages, making this difficult. However, the
acceptance of SO-DIMMs over the years has made it much easier.
7. First, power off, unplug, and remove the battery pack. Follow ESD procedures.
8. Identify the access point for the SO-DIMM. This is usually either under the keyboard or
via an access panel on the back.
9. Replace the SO-DIMM.
IT Technician
Copyright © 2007 by The McGraw-Hill Companies
Page 10 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
IV. Troubleshooting RAM
A. Memory errors can include parity errors, ECC error messages, system lockups, page faults, and
other error screens in Windows.
B. Write down memory error addresses. If the error returns with the same address each time, it is
likely a RAM stick failure.
1.
If the error address changes, it is likely not a RAM failure.
2.
System lockups and page faults often indicate RAM problem.
3.
RAM and parity errors can trigger non-maskable interrupt (NMI) that results in Blue
Screen of Death (BSoD).
4.
Not all intermittent errors are caused by bad RAM. Dying power supply, electrical
interference, and buggy applications or hardware can also produce intermittent errors.
C. Testing RAM
1.
Several RAM testing devices are available but many are expensive.
2.
Can replace one stick at a time until problems disappear.
3.
Use a software-based tester such as Memtest86.
Cool Tools
Memtest86 is a tool that can be used to test your memory. To use this tool, follow these steps.
1. Go to www.memtest86.com and download memt32.zip.
2. Unzip memt32.zip and view the extracted files.
3. Run the Install program. This will launch a DOS prompt. Place a formatted floppy in your
floppy drive and enter a at the prompt. Press ENTER. In a moment, you will have a
floppy with Memtest86 on it. It will not be readable under Windows.
4. Use this floppy to boot up on any system. Memtest86 will automatically start and run. Let it
run continuously so that you can look at the progress at different times. It takes about
an hour and half to complete a full pass of all memory tests.
V. Beyond A+
Copyright © 2007 by The McGraw-Hill Companies
Page 11 of 12
Mike Meyers’ A+ Guide to Managing and Troubleshooting PCs Instructor’s Manual
Chapter 4
A. Advances in RAM are often seen in games first. To see where RAM is headed, watch the RAM
on video cards.
B. DDR3 and DDR4 are on the horizon.
Copyright © 2007 by The McGraw-Hill Companies
Page 12 of 12