A+ PC Repair I (STEP) - Unit 07 RAM types and features

What is the best way to determine the total capacity and specific type of RAM your system can handle? A. Check the motherboard book. B. Open the case and inspect the RAM. C. Check the Device Manager. D. Check the System utility in the Control Panel.

A. Check the motherboard book.

Cindy installs a second stick of DDR2 RAM into her Core 2 Duo system, bringing the total system memory up to 2 GB. Within a short period of time, though, she begins experiencing Blue Screens of Death. What could the problem be? A. She installed faulty RAM. B. The motherboard could only handle 1 GB of RAM. C. The motherboard needed dual-channel RAM. D. There is no problem. Windows always does this initially, but gets better after crashing a few times.

A. She installed faulty RAM.

Steve adds a second 1-GB 240-pin DIMM to his PC, which should bring the total RAM in the system up to 2 GB. The PC has an Intel Core 2 Duo 3-GHz processor and three 240-pin DIMM slots on the motherboard. When he turns on the PC, however, only 1 GB of RAM shows up during the RAM count. Which of the following is most likely to be the problem? A. Steve failed to seat the RAM properly. B. Steve put DDR SDRAM in a DDR 2 slot. C. The CPU cannot handle 2 GB of RAM. D. The motherboard can use only one RAM slot at a time.

A. Steve failed to seat the RAM properly.

Which of the following Control Panel applets will display the amount of RAM in your PC? A. System B. Devices and Printers C. Device Manager D. Action Center

A. System

RAM Compatibility

An important point about DDR, DDR2, and DDR3 is that they "ARE NOT" compatible with each other. You can't use any version in a slot designed for another type. For example, you can use DDR3 DIMMs only in DDR3 slots. From a usability perspective, that's not so great, but if you're trying to remember which types are compatible, it's a lot easier. You can't mix and match them. Figure 3-5 shows a comparison of the keyings of DDR, DDR2, and DDR3, with a dotted line as a reference through the middle of each one. You can see that the notched key at the bottom of the circuit card is different for each. The standards aren't compatible, and this keying prevents technicians from inserting a DIMM into the wrong slot. A key consideration when purchasing RAM is to ensure that the RAM speeds are supported by the motherboard. If the speeds don't match, the motherboard defaults to the slower speed. For example, if your motherboard has a 100-MHz clock and you install PC3-12800 RAM, the RAM will run at 100 MHz instead of 200 MHz. It still works, but you won't get the benefit of the higher-speed RAM. EXAM TIP You might need to shop for memory, either to replace memory in your own system or to help someone else. If you can master how memory is named and marketed, you'll be able to identify the correct memory to purchase. In addition to matching the RAM speed with the motherboard speed, you should also match the RAM speed within banks when using dual-channel and triple-channel configurations. If one DIMM in a bank fails, you should replace both with a matched set. However, if you have to replace the failed DIMM with a spare, look for a spare that uses the same speed. For example, if Bank 0 currently has two PC3-12800 sticks and one fails, you should replace the failed stick with a PC3-12800 stick. PC3-12800 uses a 200-MHz clock. If you replaced it with a PC3-6400 (designed for a 100-MHz clock), both sticks would run at the slower speed or revert to single channel.

What is the primary reason that DDR2 RAM is faster than DDR RAM? A. The core speed of the DDR2 RAM chips is faster. B. The input/output speed of the DDR2 RAM is faster. C. DDR RAM is single-channel and DDR2 RAM is dual-channel. D. DDR RAM uses 184-pin DIMMs and DDR2 uses 240-pin DIMMs.

B. The input/output speed of the DDR2 RAM is faster.

Gregor installed a third stick of known good RAM into his Core i7 system, bringing the total amount of RAM up to 3 GB. Within a few days, though, he started having random lockups and reboots, especially when doing memory-intensive tasks such as gaming. What is most likely the problem? A. Gregor installed DDR RAM into a DDR2 system. B. Gregor installed DDR2 RAM into a DDR3 system. C. Gregor installed RAM that didn't match the speed or quality of the RAM in the system. D. Gregor installed RAM that exceeded the speed of the RAM in the system.

C. Gregor installed RAM that didn't match the speed or quality of the RAM in the system.

What is the term for the delay in the RAM's response to a request from the MCC? A. Variance B. MCC gap C. Latency D. Fetch interval

C. Latency

Silas has an AMD-based motherboard with two sticks of DDR2 RAM installed in two of the three RAM slots, for a total of 2 GB of system memory. When he runs CPU-Z to test the system, he notices that the software claims he's running single-channel memory. What could be the problem? (Select the best answer.) A. His motherboard only supports single-channel memory. B. His motherboard only supports dual-channel memory with DDR RAM, not DDR2. C. He needs to install a third RAM stick to enable dual-channel memory. D. He needs to move one of the installed sticks to a different slot to activate dual-channel memory.

D. He needs to move one of the installed sticks to a different slot to activate dual-channel memory.

Scott wants to add 512 MB of PC100 SDRAM to an useful desktop system. The system has a 100-MHz motherboard and currently has 256 MB of non-ECC SDRAM in the system. What else does he need to know before installing? A. What speed of RAM he needs. B. What type of RAM he needs. C. How many pins the RAM has. D. If the system can handle that much RAM.

D. If the system can handle that much RAM.

Rico has a motherboard with four RAM slots that doesn't seem to work. He has two RDRAM RIMMs installed, for a total of 1 GB of memory, but the system won't boot. What is likely to be the problem? A. The motherboard requires SDRAM, not RDRAM. B. The motherboard requires DDR SDRAM, not RDRAM. C. The motherboard requires all four slots filled with RDRAM. D. The motherboard requires the two empty slots to be filled with CRIMMs for termination.

D. The motherboard requires the two empty slots to be filled with CRIMMs for termination.

DDR2

DDR2 doubles the data rate of DDR. DDR2 is faster and uses less power than DDR. DDR2 uses a 240-pin DIMM that's not compatible with DDR or DDR3.

DDR3

DDR3 doubles the data rate of DDR2. It uses double pumping and further modifies the way that data is processed. It can transfer four times as much data as DDR and eight times as much data as SDRAM. DDR3 is faster and uses less power than DDR2. DDR3 uses a 240-pin DIMM that's not compatible with DDR or DDR2.

DDR

Double Data Rate SDRAM (DDR SDRAM, or SDRAM II, or simply DDR) is an improved version of SDRAM. While SDRAM uses only the leading edge of the clock each of the DDR SDRAM versions uses both the leading and trailing edge of the clock. DDR runs twice as fast as regular SDRAM, has one notch, and uses 184 pins. Instead of processing data for each beat of the system clock, as regular SDRAM does, it processes data when the beat rises and again when it falls, doubling the data rate of memory. If a motherboard runs at 200 MHz, DDR memory runs at 400 MHz.

SODIMM

Laptops use a smaller version of a DIMM called a SO-DIMM (small outline DIMM and pronounced "sew-dim"). MicroDIMMs are used on subnotebook computers and are smaller than SO-DIMMs. DDR SDRAM SODIMM: 200 pins DDR2 SDRAM SODIMM: 144 or 200 pins DDR3 SDRAM SODIMM: 204 pins

RAM Types: - RAM configurations -- Single channel vs. dual channel vs. triple channel

Many motherboards and CPUs support single-channel, dual-channel, and triple-channel memory architectures. Each single channel represents a separate 64-bit line of communication that can be accessed independently. With dual channel, the system can access 128 bits at a time; triple channel gives it access to 192 bits at a time. Using dual and triple channels provides an additional performance enhancement to DDR, DDR2, and DDR3, in addition to double pumping and other enhancements provided by the DDR versions. If you use a dual-channel motherboard with DDR3, it doubles the throughput of DDR3, providing 16 times more data throughput than SDRAM. If you are upgrading a computer's memory, it's important to understand these channels. You can purchase DIMMs in matched pairs. Where you install each DIMM determines how many channels your system will use and can affect the performance of RAM. Dual-channel motherboards are very common. If you look at a dual-channel motherboard, you see that it has four memory slots, two slots of one color and two slots of another color. Figure 3-3 shows a diagram of four memory slots labeled for a motherboard using an Intel-based CPU. Slots 1 and 3 are one color, and slots 2 and 4 are another color. Slots: Each slot can accept one DIMM. Banks: A bank is composed of two slots. In Figure 3-3, Bank 0 includes slots 1 and 3 and these two slots are normally blue. Bank 1 includes slots 2 and 4 and these slots are normally black. This is standard for Intel CPU-based motherboards. Channels: Each channel represents a separate 64-bit communication path. Slots 1 and 2 make up one channel, and slots 3 and 4 make up the second channel. EXAM TIP: On most motherboards, the slots are color-coded to identify the banks. Slots of the same color indicate the same bank, and matched pairs should be installed in these slots. You can install a single DIMM in slot 1, and the system will have a single-channel RAM. You can purchase DIMMs in matched pairs, and it's important to know in which slots to install them. For the best performance, you should install matched DIMMs in the same bank. Looking at Figure 3-3, you should install the matched pair of DIMMs in slots 1 and 3 (Bank 0), leaving slots 2 and 4 empty. The system will take advantage of the dual-channel architecture by using two separate 64-bit channels. What happens if you install the DIMMs in slots 1 and 2 instead? The system will still work; however, both DIMMs are installed in channel 1, so the system will work with only a single channel. RAM will be about half as fast as it could be if it were installed correctly to take advantage of the dual channels. Figure 3-3 and the previous explanation describe the color coding, banks, and channels for Intel-based CPU motherboards. However, most motherboards designed for AMD CPUs are organized differently, as shown in Figure 3-4. On these motherboards, slots 1 and 2 make up Bank 0, and slots 3 and 4 make up Bank 1. Channel 1 includes slots 1 and 3, and channel 2 includes slots 2 and 4. While this can be confusing between different motherboards, the good news is that most motherboard manufacturers use the same color for each bank. For Intel-based motherboards, Bank 0 includes slots 1 and 3, and these will be the same color (often blue). Bank 1 includes slots 2 and 4, and they will be a different color (often black). AMD motherboards also use one color for Bank 0 (slots 1 and 2) and another color for Bank 1 (slots 3 and 4). EXAM TIP: Many motherboards allow the use of different size DIMMs in different channels. However, for the system to use the multichannel capability, each DIMM within a bank must be the same size. If one DIMM in a bank is 1 GB and the second DIMM in the bank is 2 GB, the sizes are different and the system will use single channel. Also, you can use different speed DIMMs in the same bank, although this is not recommended. The speed of the bank will default to the lower-speed DIMM or, in some cases, to single channel.

RAM Types: - Parity vs. non-parity

Older SIMMs used an error-checking technology called parity. Using parity checking, a ninth bit is stored with every 8 bits in a byte. If memory is using odd parity, it makes the ninth or parity bit either a 1 or a 0, to make the number of ones in the nine bits odd. If it uses even parity, it makes the parity bit a 1 or a 0 to make the number of ones in the 9 bits even. Later, when the byte is read back, the memory controller checks the odd or even state. If the number of bits is not an odd number for odd parity or an even number for even parity, a parity error occurs. A parity error always causes the system to halt. On the screen, you see the error message "Parity Error 1" or "Parity Error 2" or a similar error message about parity. Parity Error 1 is a parity error on the motherboard; Parity Error 2 is a parity error on an expansion card.

RAM Types: - RAM configurations -- Triple channel

On some motherboards, you see six DIMM slots instead of four. This indicates the system supports triple-channel memory usage. Table 3-1 shows the configuration of the slots, banks, and channels for a motherboard using triple-channel RAM. Slots in each bank are commonly the same color, so you might see a motherboard with Bank 0 slots (slots 1, 3, and 5) all blue and with Bank 1 slots all black. Triple-channel DIMMs are sold in matched sets of three, similar to how dual-channel DIMMs are sold in matched pairs. When you install triple-channel DIMMs, you should install the matched set in the same bank. For example, if you bought one set, you'd install it in slots 1, 3, and 5.

RAM:

Random access memory (RAM) temporarily holds data and instructions as the CPU processes them and that the memory modules used on a motherboard are made of Dynamic RAM or DRAM. DRAM loses its data rapidly, and the memory controller must refresh it several thousand times a second. RAM is stored on memory modules, which are installed in memory slots on the motherboard. Several variations of DRAM have evolved over the years. Here are the four major categories of memory modules: - DIMM (dual inline memory module): All new motherboards for desktops sold today use this type of memory module. - SO-DIMM (small outline DIMM and pronounced "sew-dim"): Laptops use this smaller version of a DIMM.

DIMM

SDRAM made its debut in 1996 on a stick called a dual inline memory module (DIMM). The early SDRAM DIMMs came in a wide variety of pin sizes. The most common pin sizes found on desktops were the 168-pin variety DIMMs use a 64-bit data path. (Some early DIMMs had a 128-bit data path, but they're now obsolete.) A DIMM (dual inline memory module) gets its name because it has independent pins on opposite sides of the module. Early DIMMs did not run in sync with the system clock because they were too slow to keep up. Their speeds are measured in nanoseconds (ns), which is how long it takes for the module to read or write data. DDR SDRAM DIMM: 184 pins DDR2 SDRAM DIMM: 240 pins DDR3 SDRAM DIMM: 240 pins

RAM Speed

Some RAM is faster than other RAM, and with faster RAM you often see faster overall performance. As you'd expect, faster RAM is more expensive. If you're shopping for RAM, you want to ensure that you buy exactly what you need. This includes the correct DDR version, the correct number of channels if your motherboard supports multiple channels, and the correct speed. The speed of RAM is expressed as the number of bytes it can transfer in a second (B/s) or, more commonly, as megabytes per second (MB/s). However, the speed of most RAM isn't listed plainly. Instead, it's listed using standard names and module names such as DDR3-800 or PC3-12800, respectively. These names indicate their speed, but not directly. If you need to shop for RAM, you need to understand these names and how they relate to the speed. You can calculate the overall speed of any SDRAM DDR type by using a specific mathematical formula for that type. The formula includes the speed of the clock (Clk), a clock multiplier (Clk Mult) for DDR2 and DDR3, and doubling from double pumping (DP). The speed is calculated for a single channel, which is 64 bits wide, and then converted to bytes by dividing it by 8. The following formulas show how to calculate the speed of each of the DDR versions by using a 100-MHz clock: - DDR speed calculation: Clk x 2 (DP) x 64 (bits) / 8 (bytes) 100 MHz x 2 x 64 / 8 = 1,600 MB/s - DDR2 speed calculation: Clk x 2 (Clk Mult) x 2 (DP) x 64 (bits) / 8 (bytes) 100 MHz x 2 x 2 x 64 / 8 = 3,200 MB/s - DDR3 speed calculation: Clk x 4 (Clk Mult) x 2 (DP) x 64 (bits) / 8 (bytes) 100 MHz x 4 x 2 x 64 / 8 = 6,400 MB/s Table 3-2 shows how these speeds relate to the different naming conventions used with DDR types. You can see that the standard name is derived from the clock, the clock multiplier, and double pumping. For example, DDR3 uses a 4-times multiplier and double pumping. Therefore, it's eight times faster than SDRAM. The standard name is derived by multiplying the clock by 8. The module name is a little more cryptic, but if you calculate the speed by using the clock, you can see that the PC name indicates the calculated speed in MB/s. Also, you can see that the names include the version (DDR, DDR2, or DDR3). NOTE: SOME ROUNDING ALLOWED If you enjoy math, you can plug the fractional number 166 2/3 into the speed calculation formulas and see that they don't work out exactly. For example, DDR2-667 works out to about 5333.312 MB/s. Some manufacturers advertise this as PC2-5300, while others round it up to PC2-5400. Each DDR version supports multiple clock speeds, and each newer version supports faster clocks. Some of the clock speeds supported by different DDR versions are as follows: DDR: 100, 133 1/3, 166 2/3, and 200 MHz DDR2: 100, 133 1/3, 166 2/3, 200, and 266 2/3 MHz DDR3: 100, 133 1/3, 166 2/3, 200, 266 2/3, and 400 MHz"

SDRAM

Synchronized memory runs in step with the processor and system clock, and its speeds are measured just as processor and bus speeds are measured in MHz. Almost all primary DRAM used in computers today is SDRAM, but it's often listed as DRAM to avoid confusion with SRAM. (SRAM is static RAM used in processor memory caches, and SDRAM is dynamic RAM used on DIMMs.) SDRAM has two notches, and uses 168 pins.

RAM Types: - ECC vs. non-ECC

Today's PCs that need to watch for RAM errors use a special type of RAM called Error Correction Code RAM (ECC RAM). ECC is a major advance in error checking on DRAM. First, ECC detects any time a single bit is incorrect. Second, ECC fixes these errors on-the-fly. The checking and fixing come at a price, however, as ECC RAM is always slower than non-ECC RAM. ECC RAM uses additional circuitry and can detect and correct errors. This extra circuitry adds significantly to the cost of the RAM and should be purchased only when necessary. For example, spacecraft that might be exposed to solar flares commonly use ECC RAM. Additionally, some high-end scientific and financial servers need it to ensure that the data in RAM remains error-free. ECC DRAM comes in every DIMM package type and can lead to some odd-sounding numbers. You can find DDR2 or DDR3 RAM sticks, for example, that come in 240-pin, 72-bit versions. Similarly, you'll see 200-pin, 72-bit SO-DIMM format. The extra 8 bits beyond the 64-bit data stream are for the ECC. You might be tempted to say "Gee, maybe I want to try this ECC RAM." Well, don't! To take advantage of ECC RAM, you need a motherboard with an MCC designed to use ECC. Only expensive motherboards for high-end systems use ECC. The special-use-only nature of ECC makes it fairly rare. Plenty of techs with years of experience have never even seen ECC RAM. NOTE: Some memory manufacturers call the technology error checking and correction (ECC). Don't be thrown off if you see the phrase it's the same thing, just a different marketing slant for error correction code.

RAM Types: - Single sided vs. double sided

You'd think that single-sided and double-sided RAM refers to how many sides of a DIMM have chips. That makes sense, but it's not entirely accurate. Instead, single sided or double sided refers to how a system can access the RAM. In double-sided RAM, the RAM is separated into two groups known as ranks, and the system can access only one rank at a time. If it needs to access the other rank, it needs to switch to the other rank. In contrast, single-sided (or single-rank) RAM is in a single group; the system can access all RAM on the DIMM without switching. If you have a DIMM with chips on only one side, it is most likely a single-sided (single-rank) DIMM. However, if it has chips on both sides, it can be single rank, dual rank, or even quad rank. You often have to dig into the specs to determine how many ranks it is using. Usually, you'd think that double is better than single, but in this case, more rank is not better. Switching back and forth between ranks takes time and slows down the RAM. Single-sided RAM doesn't switch, and if all other factors are the same, single-sided RAM is faster than double-sided RAM. NOTE: DUAL-SIDED IS NOT DUAL CHANNEL Dual-sided (or dual-ranked) is not the same as dual channel. Dual channel improves performance, but a dual-ranked DIMM doesn't perform as well as a single-ranked DIMM.