Chapter 4: RAM
Types of RAM
A.
Synchronous DRAM (SDRAM)
1.
Synchronized with the system clock
2.
Came on a stick called a dual inline memory module (DIMM)
3.
Came in a wide number of pins on DIMMs
a) 168 pins are common on desktops.
b) Laptops had 68-pin, 144-pin, and 172-pin micro-DIMMs.
c) Laptops also had small-outline DIMMs called SO-DIMMs of 72 pins, 144 pins, or
200 pins.
4.
Based on clock speed measured in MHz
a) Five clock speeds commonly used on the early SDRAM systems: 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 big leap in DRAM, RDRAM suffered delays in
manufacturing and was significantly more expensive than SDRAM.
3.
Commonly called a RIMM (RIMM doesn’t specifically stand for anything).
C.
Double data rate SDRAM (DDR SDRAM)
1.
Fast RAM supported by AMD and other manufacturers
2.
Doubles the throughput over SDRAM (two processes for each clock cycle)
3.
Commonly referred to as DDR, DDR RAM, and DDRAM
4.
Comes in 184-pin DIMMs
5.
Keyed slots with guide notches – cannot insert RAM in incorrect slots
6.
DDR speed rating and PC speed rating based on clock speed
a) Base clock is 100 MHz to 300 MHz with the DDR speed rating double the clock
speed.
b) 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 PC standard system RAM
8.
Can make use of dual-channel architecture
a) Similar to Rambus in how it improves performance
b) Requires two identical sticks of DDR snapped into two paired slots
D.
DDR2
1.
Speed increase comes by clock-doubling the input/output circuits on the chips.
2.
DDR2 uses 240-pin DIMM (not compatible with DDR DIMM).
E.
DDR3
1.
DDR3 has higher speeds, more efficient architecture, and 30 percent lower power
consumption than DDR2 RAM.
2.
DDR3 uses 240-pin DIMM (not compatible with DDR2).
3.
DDR3 doubles the buffer of DDR2 from 4 bits to 8 bits.
4.
Some DDR3 modules also include XMP, or Extreme Memory Profile, that enables
overclocking RAM.
5.
Some chipsets that support DDR3 also support a feature called triple-channel memory or
quad-channel architecture, which works a lot like dual-channel, but with three or four
sticks of RAM instead of two.
6.
More recent Intel and AMD systems support quad-channel memory.
7.
DDR3 I/O speeds are quadruple the clock speeds due to increased buffer size.
8.
PC rating is determined similar to how DDR2 is determined (with another doubling),
and prefixed by a 3. For example, for DDR3 with a clock speed of 200 MHz, the DDR
I/O speed would be 800 MHz, the DDR3 speed rating would be DDR3-1600, and the
PC speed rating would be PC3-12800.
F.
DDR3L/DDR3U
1.
DDR3L is a low-voltage version of DDR3.
a) Runs at 1.35V compared to 1.5V or 1.65V of regular DDR3
2.
DDR3U is ultra-low-voltage and runs at 1.25V.
3.
Low voltage means less heat generated, which is good for server farms or data centers.
4.
The DIMM is slot-compatible with DDR3.
G.
DDR4
1.
Higher density and lower voltages than DDR3
2.
Can handle higher data transfer rates
3.
Uses 288-pin DIMM, and is not backwardly compatible with DDR3 slots
H.
RAM variations
1.
Double-sided DIMMs.
a) Every type of RAM stick comes in one of two types: single-sided RAM and
double-sided RAM.
b) Some motherboards can’t use double-sided sticks.
2.
Latency refers to how quickly the RAM responds to the electrical signal.
a) Numbers reflect how many ticks of the system clock it takes before the RAM
responds.
b) RAM with a lower latency—such as CL17—is faster than RAM with a higher
latency—such as CL19.
c) The goal is to match the RAM with the motherboard.
3.
Parity and ECC
a)
b)
c)
d)
4.
Parity RAM allows the computer to detect whether an error occurred in the reading
or writing of data in memory.
Error correction code (ECC) is an improvement over parity. Not only can errors be
detected, but they can also be corrected.
ECC is slower because of the extra calculations required.
ECC is used only on higher-end workstations and servers.
Registered and buffered memory
a) Registered RAM (or buffered RAM) refers to a small register installed on some
memory modules to act as a buffer between the DIMM and the memory controller.
b) The motherboard will use either buffered or unbuffered RAM (typical consumer
RAM), not both.
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 antistatic packaging and
following strict ESD practices.
B.
Do you need more RAM?
1.
Two symptoms show the need for more RAM:
a) General system sluggishness
b) Excessive hard drive accessing
1) Programs take forever to load.
2) Running programs seem to stall and move more slowly than you would like.
2.
Virtual memory is a portion of the hard drive used as an extension of RAM.
a) A portion of an HDD or SSD is set aside as a page file or swap file.
b) When the PC starts running out of real RAM because you've loaded too many
programs, the system swaps programs from RAM to the page file, opening more
space for programs currently active.
c) Disk thrashing occurs when the operating system needs to access the page file too
frequently.
3.
System RAM recommendations
a)
32-bit Windows: 2 GB to get by; 4 GB for best results
b) 64-bit Windows: 4GB to get by; 8 GB for a solid machine; 16+ GB for any
machine doing serious, processor-intensive work
c)
macOS: minimum 2 GB; 4 GB better minimum; 8 GB for good
performance; more for peak performance
d) Linux: many distros get by on very minimal system requirements
4.
Determining current RAM capacity
a) Use the System Control Panel applet.
b) Use Performance tab in Task Manager.
5.
ReadyBoost
a) Enables the use of flash media devices as super-fast, dedicated virtual memory
Troubleshooting RAM
A.
B.
C.
Memory errors can include parity errors, ECC error messages, system lockups, page faults,
and other error screens.
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 a non-maskable interrupt (NMI) that results in a
proprietary crash screen.
a) Windows Blue Screen of Death (BSoD)
b) macOS pinwheel of death
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.
Testing RAM
1.
You can replace one stick at a time until problems disappear.
2.
Windows 7 and later include the Windows Memory Diagnostics tool, which can
automatically scan your computer’s RAM when you encounter a problem.
3.
Memtest86+ is also an example of software for testing RAM.