1. RAM
Chapter 3

2. Overview In this chapter, you will learn how to
Identify the different types of RAM packaging
Explain the varieties of DRAM
Install RAM properly
Perform basic RAM troubleshooting
Instructor Tip
When gaining attention and establishing common ground, ask questions such as, “What is RAM?” or “Who here has ever installed RAM?”
For a positive statement, tell the class, “In this lesson, we are going to learn how to recognize various forms of RAM, how it works, and how to install it properly.”

3. DRAM

4. Program Execution
Program code is copied from your hard disk into RAM before it is executed…

5. DRAM
DRAM (Dynamic Random Access Memory) is the most popular type of electronic memory
Special type of semiconductor that stores individual 1’s and 0’s using microscopic capacitors and transistors
Note: We tend to interchange the terms RAM and DRAM. Just be aware that DRAM is really a type of RAM. Most PCs use DRAM, so when we refer to the RAM we are usually talking about DRAM. When we refer to DRAM, we are talking about RAM.

6. Organizing DRAM
DRAM is considered as the standard RAM due to its low cost, high speed, and ability to store data in a relatively small package
The RAM stores programs and data in 8-bit (1-byte) chunks of memory
DRAM chips are always referenced with respect to their depth and width
1 Meg x 4
256 K x 1

7. Organizing DRAM The depth and width are measured in units of bits
They can only be differentiated using the information printed on the chip itself
The physical size and the internal organization of the chip are not directly correlated

8. Byte Size RAM

9. Multiple Rows of RAM

10. Location of DRAM The Northbridge knows the real location of the DRAM
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 DIPP chips, it is best to label RAM when you buy them so you will always be able to distinguish one from another. Parity RAM always has an odd number of chips (often three or nine), whereas non-parity always has an even number of chips.

11. RAM Sticks

12. DIPP (Dual Inline Pin Packages)
The first generation DRAM chips used DIPPs
Two rows of pins extending from either side of the package
Very delicate, making the installation process difficult
Dealing with Old RAM
Often in the PC world, old technology and ways of doing things get reimplemented with some newer technology. Learning how things worked back in the ancient days can stand a tech in good stead. Perhaps more importantly, many thousands of companies—including hospitals, auto repair places, and more—use very old, proprietary applications that keep track of medical records, inventory, and so on. If you’re called to work on one of these ancient systems, you need to know how to work with old parts, so try this. Get the use of an old computer, such as a 386 or 486. Ask your uncle or cousin or Great Aunt Edna if they have a PC collecting dust in a closet that you can use. Failing that, go to a secondhand store or market and buy one for a few dollars. Open up the system and check out the RAM. Remove the RAM from the motherboard. Replace it to familiarize yourself with how it used to be. You never know when some critical system will go down and need repair immediately—and you’re the one to do it!

13. 30-pin SIPP (Single Inline Pin Package)
SIPP is a type of package where the RAM is soldered to a small board that can be inserted in to the motherboard
Made RAM installation and removal much simpler
Plugged directly into the motherboard through a special socket
Easy to install but are delicate

14. 30-pin SIMM (Single Inline Memory Modules)
SIMMs are physically similar to SIPPs, but have no pins
Inserted into special SIMM sockets
Always 8 data bits (1 byte) wide
All nonparity 30-pin SIMMs have an even number of chips
The type of motherboard would indicate whether parity or nonparity chips are needed
Each individual SIMM is called a stick
“X 8”, “X 9”, and “X 3” are the three widths of DRAM available
Three common sizes in 30-pin SIMMs are 256 KB, 1 MB, and 4 MB

15. Different Chip Layouts on a SIMM
Label your sticks of memory – you can’t tell what size by looking at a stick of memory.

16. SIMM Chips and Parity
When purchasing SIMM chips the question is whether you need parity or not
You could get a clue from the chips already in the PC – an even (nonparity) or odd (parity) number of chips
Some PCs let you turn parity off so you could mix and match

17. Speed The system clock controls the CPU speed
The earlier types of RAM were called Fast Page Mode (FPM) RAM
Access speed (in nanoseconds) refers to the time taken by the FPM DRAM chip to supply the chipset with the requested data
Each motherboard required a certain speed
A lower access speed number means faster access.

18. Talking the Talk Each SIMM is called a stick
Never say 30-pin SIMM or ask for parity or nonparity. Instead say “by 3” or “by 8” or “by 9”. These are the most common widths
X8 is nonparity
X9 is parity
X3 is a x9 in a 3-chip package
Three common sizes are 256KB, 1 MB, 4MB – so ask for a “4x8” or “1x3”
Never give speed in nanoseconds – say I’d like some 50’s
Discussion Point
Terminology
Most PC professionals will call a RAM module a “stick.” If buying RAM, you would typically ask for a 30-pin stick, a 72-pin stick, or a 168-pin stick.
“I’d like 16 sticks of 1x8 sixties, and four
sticks of 256x9 eighties.”

19. Banking
Combining the widths of DRAM to match the width of the external data bus is called banking
The number of SIMMs that make up a bank depends on the chipset, which in turn depends on the CPU’s external data bus size

20. Banking
The most important banking rule is that all SIMMs in the same bank must be identical
The connectors where the bank is installed are also collectively called a bank
Discussion Point
Banking Math
It is really easy to figure out the banking system for PC RAM. A bank must be able to provide data to the CPU equal to the width of the CPU’s data bus. Because we know 72-pin SIMMs are 32 bits wide, you need two to equal a bank on a 64-bit Pentium. But it only takes a single 72-pin SIMM to equal a bank on a 32-bit 486 CPU.
Imagine how much room you would need on a Pentium motherboard if you were going to use 30-pin SIMMs (at 8 bits each). It would take 8 sticks of 30-pin SIMMs to equal one bank! Compare that to a single 168-pin DIMM (at 64 bits each) per bank.
128-bit CPUs are expected to be in the market soon. These would naturally require two 168-pins DIMMs per bank.

21. Banking
A bank without any SIMMs is called an unpopulated bank, and a bank filled with SIMMs is called a populated bank
A bank must be either completely populated or completely unpopulated
This formula can be used to determine the number of sticks needed to make a bank – One bank = Width of the CPU’s external data bus ÷ Width of the SIMM/DIMM
It takes four 30 pin slots in a 486 to make a bank

22. 72-pin SIMMs
Modern CPUs have 64-bit external data buses and do not use the 30-pin SIMMs
72-pin SIMMs are an inch longer than 30-pin SIMMs, and have a notch in the middle
Each 72-pin SIMM is 32-bits wide
The term “X 32” describes nonparity SIMM and “X 36” describes parity SIMM

23. Four 72-pin SIMM Slots

24. 72-pin SIMMs
A label can be used for identifying between a parity and nonparity 72-pin SIMM
Types of parity SIMMs
True (parity bit for every 8 bits)
TTL (emulates parity and costs less)

25. SIMM Sizes and Talk 1x32 = 4MB, no parity 1x36 = 4MB, parity
Thru 4, 8, 16 x 32(or 36)
All x32’s are nonparity – all x36’s are parity
The size is figured like this: 2x32 means 2MB of 32-bits, or 8MB of 8-bits (size=8MB)
“I’d like 4 sticks of 4x32 fifties”

26. DIMM (Dual Inline Memory Module)
The 168-pin DIMM is the most popular DRAM package in use today
Extra pins to handle functions such as buffering and ECC
144-pin SO-DIMMs (Small Outline) are used in laptops

27. The Magic Banking Formula
One bank = width of the CPU’s external bus ÷ width of the SIMM or DIMM
How many 30-pin SIMMs are needed to make a bank on a 486?
A 486 has a 32-bit external data bus
30-pin SIMMs are 8 bits wide
We need four (32 ÷ 8) 30-pin SIMMS per bank
How many 168-pin DIMMs are need to make a bank on a Pentium III?
A Pentium III has a 64-bit external data bus
168-bit DIMMS are 64 bits wide
We need one (64 ÷ 64) DIMM per bank
30-pin SIMMS
8 bits wide
72-pin SIMMS
32 bits wide
168-pin DIMMs
64 bits wide

28. CPUs, External Data Bus, and Address bus Sizes
Summary
CPUs, External Data Bus, and Address bus Sizes
CPU
External Data Bus Bits
Address Bus Bits
Intel 8086 16 20
Intel 8088 8
Intel 80286 24
Intel 80386DX 32
Intel 80386SX
AMD AM386DX
AMD AM386SX
Intel 80486DX
AMD AM486DX
Intel Pentium 64
AMD Athlon
AMD Duron
Intel Pentium Pro
Intel Pentium II
Intel Pentium III
Exercise
RAM Identification
This is a good opportunity to have students identify many types of RAM packages. Hold up various RAM sticks and ask individual students to identify them. Or you might give an impromptu written quiz: Have the students take out a sheet of paper, and when you hold up the RAM stick, ask them to write down its type. Alternately, you can pass around various RAM sticks with numbered labels on them. Ask the students to write down the number and the type of RAM stick for each.

29. Improvements in DRAM Technology

30. EDO DRAM
EDO (Extended Data Out) is a type of DRAM that provides the system quicker access to data
Looks exactly like the regular DRAM, so you should label it
To take advantage of the EDO, the chipset must be designed to handle it
Now considered obsolete

31. SDRAM
SDRAM (Synchronous Dynamic Random Access RAM) are tied to the system clocks
Faster than DRAMs
Only available on DIMMs
Use clock speed instead of access speed
SDRAM is always a DIMM, but a DIMM isn’t always SDRAM
What makes SDRAM faster?
Before SDRAM the system had to send the signal to DRAM, wait a certain number of clicks (this number was rounded up just to be sure the data would be ready), and then access the RAM for the data. Using the system clock, the chipset now knows exactly when the data is ready – speeding up the process

32. PC100/133 Standards
The PC100 and 133 standards define the construction of a high-speed DRAM
Require the use of DIMMs or SO-DIMMs, and a unique chip called the serial presence detect (SPD) to be installed on every DIMM stick
The SPD provides the system with all the details of DIMM

33. ECC
ECC (Error Correction Code) is a special type of RAM used by high-end systems
Major advance in error checking on DRAM
RAM sticks of any size can use the ECC DRAM, but it is most common as 168-pin DIMMs
A motherboard should be designed to use ECC, to take advantage of the ECC RAM
Tech Tip
Registered DRAM
Most servers and many high-end workstations sport a DRAM variant called registered DRAM that facilitates high-volume data flow in and out of RAM. Registered DRAM has logic circuits— quite logically named registers—that buffer control signals to synchronize with the system clock. This sort of RAM helps these systems keep track of the hugely complex data transfers and manage multiple sticks of RAM. Typical home and office PCs, in contrast, use unbuffered (meaning without registers) DRAM, optimizing for speed rather than perfect data transfers.

34. RDRAM RDRAM (Rambus DRAM) is a new type of RAM Speeds of up to 800 MHz
Comes on sticks called RIMMs
184-pin for desktops and 160-pin SO-RIMM for laptops
All slots must be populated - unused slots must have a CRIMM (Continuity RIMM)
Terminology
RDRAM, or Rambus DRAM, is also called RIMM sticks.
RDRAM speeds start with “PC” followed by the speed, so 800 MHz RDRAM is known as PC800 and 1066 MHz RDRAM is known as PC1066.

35. DDR SDRAM (Double Data Rate)
DDR SDRAM (Double Data Rate SDRAM) doubles the throughput of SDRAM
184-pin DIMM packages
Speed of 200 or 266 MH.
Used in lower-end systems

36. Dual-Channel Architecture
Dual-channel architectures use two sticks of RAM together to increase throughput
Double-sided SIMMs/DIMMs
Double-side sticks have chips on both sides
DUAL DDR has a few quirks such as this one:
Motherboards that use NVIDIA’s nForce2 chipset have three DDR SDRAM slots, but dual channel only works if you populate the two blue dual slots and leave the third black slot empty
While every PC uses DRAM in one of its many variations for their RAM, other forms of RAM are found in PCs with names like VRAM and SGRAM.

37. Installing RAM
The A+ Certification Core Hardware Exam wants you to know how to install older types of RAM, not just the RAM in common use today.

38. Do You Need RAM? Two symptoms point to needing more RAM
General system sluggishness
Disk thrashing or excessive hard drive accessing
How do know if your disk is thrashing?
Observe the LED at work
Use FreeMeter (

39. Mixing DRAM Packages
Modern motherboards have been designed with slots for more than one type of DRAM
The motherboard jumper may have to be moved to enable two different types of DRAMs to work together
Most current motherboards have only DIMM slots

40. Speed
Mixing DRAM speeds can cause the system to lock up every few seconds, leading to data corruption
Experimenting won’t harm anything but the data
You can use faster DRAM than the motherboard recommends but won’t see an increase in performance
You can put different speeds of DRAM in different banks as long as they are both faster than the speed specified
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 (i.e., PC133 on a 100 MHz motherboard), you will not see any improvements over normal operations.

41. Banks All systems number their banks, usually starting at zero
All banks do not take all sizes of DRAM
Some systems require you to populate bank 0 first…most systems don’t care

42. Installing SIMMs
A notch on one side will prevent you from installing it incorrectly
Insert on an angle, then rotate up and snap into place
What is wrong?

43. Installing DIMMs Swing the side tabs away from upright
Push the DIMM down somewhat hard – the two tabs should move back into place
Tech Tip
Mixing PC100 and PC133
Although in theory it should work to add a PC133 stick to a system running at 100 MHz that already has a stick or two of PC100, such a move can greatly destabilize a PC. The frustrating part about this is that mixing destabilizes some systems, but not others. Worse, it doesn’t seem to matter which chipset or processor type the systems have. A motherboard from one manufacturer supporting a Pentium III with a VIA chipset will have no problems, for example, but a motherboard from another manufacturer with an identical chipset and CPU combination will crash from here to Tuesday. About the best advice I can offer is don’t mix at all and thus avoid all the fuss.

44. Installing SO-DIMMs in Laptops
Remove the panel or lift the keyboard
Slide the pins into position, snap the SO-DIMM down into the retaining clips
Make sure the system is off
No AC connection
Remove all batteries
Exercise
RAM Installation
Have the students install various RAM sticks in various systems. Again, and as always, reinforce proper ESD protection.
You can install the RAM improperly, such as by mismatching the RAM or ignoring banking rules, and ask the students to diagnose the problem.

45. Check the RAM
A halt before the RAM check could indicate improperly installed RAM

46. Troubleshooting RAM
Parity errors, ECC error messages, system lockups, and page faults are a few types of memory errors
Real and phantom are the two types of parity errors
If you get the error “Parity error at xxxxx”, write down the address – a real parity error will occur at the same place in memory and indicates a bad RAM stick
Real errors are errors that the chipsets detect from the parity chip

47. Troubleshooting RAM
Phantom errors arise due to software problems, heat or dust, and fluctuations in force
NMI (non-maskable interrupt) is a type of interruption that cannot be ignored by the CPU…resulting in a Blue Screen of Death (BSoD)
Bad RAM and parity error can trigger an NMI
If you get intermittent parity errors, check out the power supply

48. Testing RAM
Hardware RAM testing devices can be used to troubleshoot errors
An economical option is to replace the existing sticks with new ones

49. MRAM Desirable RAM characteristics are
Non-volatility
Low price
Fast speed
Low power consumption
By mid-decade a new type of RAM should become available called MRAM (Magnetoresistive Random Access Memory)
Will use magnetism instead of electrical charges
Like videotapes, audio cassettes, and hard drives
Smaller chip size, faster, cheaper