Computer Memory

Explain the progression of the types of memory chips used?

- A DIP (dual in-line package) chip has a row of legs running down each side. -The oldest motherboards use DIP chips for the DRAM. - SIMMs(single in-line memory modules) came along next. Two types of SIMMs were used: 30-pin and 72-pin. - The memory chip used today is aDIMM

Problem: The Computer Won't Boot/Intermittently Shuts Down

- If there is no RAM in the computer, or the RAM is damaged, or not installed securely, it can prevent the computer from doing anything at all, aside from draining electricity from your AC outlet. For example, the power supply fan turns but nothing else—no beeps and no displays. First, if the RAM were just installed, make sure that the RAM is compatible. Next, and in general, try reseating the RAM before you attempt to troubleshoot a CPU or motherboard. Add RAM if none exists. - If you suspect faulty RAM, corroded contacts, or a faulty RAM slot, you can try taking the RAM out, cleaning the RAM and RAM slot if necessary (with compressed air), and putting the RAM back in. - Next, if the computer has two memory modules, try booting it with just one (if the motherboard allows it), or try moving memory modules to different slots. - Use a POST card tester. - If necessary, replace the memory module with an identical one (if you have an extra one handy), or at worst, purchase a new one if you have identified the memory module as the source of the problem. - Heat sinks can be purchased for RAM. In some cases, RAM can overheat and cause intermittent shutdowns.

Fully Buffered Memory

- introduces an advanced memory buffer between the memory controller and the memory module. - For this to work, a completely different memory module must be used, with the notch in a different location, making it incompatible with motherboards that support regular DDR or registered DDR. - This kind of memory module is known as a FB-DIMM. - An example would be PC3-10600F or PC3-10600FB.

DDR

Double Data Rate (DDR) is by far the most commonly used RAM on the planet. DDR is synchronized to the memory clock just like SDRAM; it's also called DDR SDRAM.

What is the main memory that the CPU uses to store or retrieve data.

Random-access memory (RAM)

Memory Latency/Column Address Strobe (CAS)

- Memory latency or Column Address Strobe (CAS) latency happens when a memory controller tries to access data from a memory module. It is a slight delay (usually measured in nanoseconds) while the memory module responds to the memory controller. - It is given a rating of CAS, or more commonly CL. - The higher the CL number, the longer the delay. - The general range of DDR3 memory is between CL5 and CL10. - However, the difference between the ratings is small, so it usually has an effect only on users that run powerful memory-intensive applications, for instance graphics rendering. Video editors, graphic designers, and gamers.

Registered Memory

- Registered memory (also known as buffered memory) improves the integrity of the signal between RAM and the memory controller by electrically buffering the signals using an extra register. - This is done for stability, especially when using multiple memory modules; however, this could cause additional latency. - An example of DDR3 registered memory would be PC3-10600R.

Problem: BIOS indicates a memory error:

- The BIOS can indicate a memory error through a gray message on the screen and a flashing cursor, or by beeping. If it beeps, you need to reference your motherboard documentation for the specific beep codes. - Sometimes a BIOS setting can be incorrect. For example, maybe the RAM's latency setting or some other setting needs to be modified. If the computer has a saved version of the BIOS settings, you can try reverting to them, or you can try loading the BIOS defaults. Sometimes the BIOS indicates the wrong amount of RAM. If this is the case, check the RAM as explained in the first bullet. Finally, a BIOS update can be the cure; perhaps the BIOS just doesn't have the programming necessary to identify the latest type of RAM that was installed.

Single-sided vs. Double-sided

- not quite literal. - Use your motherboard's documentation or a memory manufacturer's database to verify whether your motherboard accepts single-sided or double-sided memory modules, and acquire the compatible RAM from a reputable vendor. -Single-sided refers to a memory module with a single "bank" of chips. The computer's memory controller can access all the chips at once. The memory module might have chips on both physical sides, or only on one side, but it is known as single-sided memory module. - Double-sided memory modules have their chips divided into two "sides" known as banks. Only one "side" can be seen by the computer at any time. To use the second half of the storage available, the computer must switch to the second bank and can no longer read or write to the first half until it switches back again.

Single Channel

- original RAM architecture. -In modern computers, there is a 64-bit bus (or data channel) between the memory and the memory controller. -One or more sticks of RAM can be installed into the motherboard, but they share the same channel.

Rambus DRAM/RIMM

-Rambus DRAM is another type of synchronous dynamic RAM designed by the Rambus Corporation and used primarily at the turn of the millennium. -Because RDRAM was proprietary and not part of the JEDEC standard, many manufacturers would not support or license it. This and other factors led to the general demise of RDRAM -For PCs it's difficult to find it today, but a few components and gaming consoles use it. The chances of you working with it in a PC or seeing questions on the exam about it are unlikely -A few examples of RDRAM (also known as RIMMs) are PC800 (single channel, 16-bits wide, 1600 MB/ s bandwidth), the more advanced RIMM 3200 (dual channel, 32-bits wide, 3200 MB/ s), and RIMM 6400 (dual channel, 32-bits wide, 6400 MB/ s.)

Triple Channel

-Triple-channel architecture accesses three memory modules at the same time, in effect a 192-bit bus. -In this less common setup; a motherboard would have one of two configurations: 1) The first would be three channels of two different color memory slots each. A bank of RAM would include Channel A DIMM 0, Channel B DIMM 0, and Channel C DIMM 0. The first bank is usually blue, and the second bank is black. 2) The other configuration would have three blue slots, each its own channel, and a separate black slot that can be used for single channel mode, if the triple-channel option is not used. ***Triple channel is limited to Intel Core i7-900 series processors and the LGA 1366 socket.

Double Channel

-essentially doubles the data throughput -Two separate 64-bit channels are employed together resulting in a 128-bit bus. -To incorporate this, the proper motherboard will have color-coded matching banks. -Both DIMMs should be identical for best performance. This means the capacity, speed, and number of chips must be the same on both DIMMs. **The key is to install in pairs of the same color.

Where can the memory controller be? (older vs. newer)

1) Within the chipset: In older systems the memory controller is within the northbridge, which Intel calls the Memory Controller Hub (MCH). 2) Integrated to the CPU: In most of today's systems, the memory controller is part of the CPU (known as "on-die"). It does the same job regardless, but it's going to be faster than a northbridge memory controller.

Steps to Install RAM

1- Select the Correct Memory Module (Motherboard Compatibility: Use Memory Card Manufacturer Website) 2- Employ ESD Prevention Methods 3- Ready the MOBO (clear away any cables/devices that could get in the way) 4- Install RAM (hold by edges, look for orientation markings, touch chassis before touching RAM) 5- Test the Installation (With case open, boot, make sure BIOS recognizes RAM as the right type and speed, boot to O/S. Restart a few times to ensure it works.

What is the cause of most RAM problems?

A lot of the issues you see are because a user has purchased and installed a memory stick that is not compatible, or is semi-compatible, with the mobo. wrong speed, incorrect capacity, improper configuration, and so on. -Another possibility is that the RAM was damaged by ESD, and this damage manifests itself as intermittent problems.

What is the equation for Data Transfer Rate/Bandwith

Clock speed × bytes × 2 = Data Transfer Rate Example: 100 MHz × 8 × 2 = 1,600 MB/ s

DDR2

DDR2 builds on the original DDR specification by decreasing voltage (to 1.8 V) and by increasing speed. It increases speed through faster signaling, which requires additional pins. Standard DDR2 DIMMs have 240 pins and cannot be used in DDR1 memory slots.

DDR3

DDR3 was designed for lower power consumption, and higher reliability, while enabling higher levels of performance. 240-pin DDR3 DIMMs are similar to DDR2 DIMMs but are not backward compatible. As of 2012, DDR3 is the most common DIMM installed in new PCs, due to its capability to transfer twice as much data, using less voltage (1.2 to 1.5 V), and basically working faster and more efficiently.

DDR4

DDR4 modules have been introduced but are not mainstream. They have a lower voltage range, from 1.05 to 1.2 V than does DDR3 and are expected to go as high as 4,266 MT/ s. DDR4 has been delayed and may continue to be delayed for a while due to compatibility issues with other hardware.

What is the difference between DIMMs and SIMMs?

Dual in-line memory modules (DIMMs) have been in use for more than a decade. They are the successor to the single in-line memory module (SIMM). The main difference between the two is that DIMMs have separate electrical contacts on each side of the module (or stick), whereas SIMMs might have contacts on both sides, but they are redundant.

DRAM

Dynamic random-access memory (DRAM) is RAM that does need to be periodically refreshed. -This is because every bit of information stored in DRAM is stored in a separate capacitor. These capacitors lose their charge over time, causing the data to fade unless the capacitor is recharged or refreshed. -With DRAM, the 1s and 0s inside the chip must be refreshed. Over time, the charge, which represents information inside a DRAM chip, leaks out. The information, stored in 1s and 0s, is periodically rewritten to the memory chip through the refreshing process. The refreshing is accomplished inside the DRAM while other processing occurs. Refreshing is one reason DRAM chips are slower than SRAM.

ECC vs. non-ECC

Error Correction Code (ECC) in RAM can detect and correct errors. Real-time applications might use ECC RAM. Like parity RAM, additional information needs to be stored, and more resources are used in general. This RAM is the slowest and most expensive of RAM types. DDR3 ECC modules are identified with either the letter E, or ECC, for example PC3-10600E. -Most new PCs do not need or support parity or ECC RAM due to the low possibility of data corruption. If it is supported, but not necessary, these options can be disabled in the BIOS.

Hows does the Memory Controller move data?

It does this by moving the data along the address bus, which connects the memory controller to RAM.

Quadruple Channel

Quadruple channel architecture takes this idea to the next level. It works only when four identical memory modules are placed in the correct slots.

Parity vs. non-parity

RAM parity is when memory stores an extra bit (known as a parity bit) used for error detection. This means that the memory module can store 9 bits instead of 8 bits for every byte of data. So, parity RAM includes this extra bit, and the more common nonparity RAM does not. Parity RAM might be required when data integrity is a necessity.

What is SDRAM voltage?

SDRAM voltage is 3.3 volts.

What are the DDR2 standards? (+clock speed, t/s,transfer rate, module name)

SEE CHART

What are the DDR3 standards? (+clock speed, t/s,transfer rate, module name)

SEE CHART

SRAM

Static random-access memory (SRAM) is RAM that does not need to be periodically refreshed. *Memory refreshing is common to other types of RAM and is basically the act of reading information from a specific area of memory and immediately rewriting that information back to the same area without modifying it.

SDRAM

Synchronous DRAM (SDRAM) is DRAM that is synchronized to the base clock of the motherboard (also referred to as the system bus speed). -If your system bus (and corresponding memory bus) were 100 MHz, you would want to install compatible 100 MHz SDRAM because that SDRAM receives its clock signal from the system bus on the motherboard.

Memory Controller

The go-between; basically, information is stored in and retrieved from RAM with the help of the memory controller. When the CPU wants to store or retrieve data to and from RAM, the memory controller is the chip responsible for getting the job done.

What kind of memory chip is used today? How much pins...

The memory chip used today is a DIMM (dual in-line memory module), SDRAM 168 pins, DDR1 184, or DDR2/3 240 pins.

DDR1

The original DDR (aka DDR1) is actually SDRAM that has been double-pumped, meaning that twice the data is transferred but at the same clock speed. It does this by transferring data on the rising and falling edges of each clock signal (every cycle).

Problem: Page faults (hard faults), out-of-memory or low-on-virtual memory errors:

These are usually issues with the operating system or application that was running. However, you see less and less of these with each new Windows version. If a particular application keeps failing, or if you get a particular message listing a specific memory location over and over again, it can indicate a physical problem with RAM. Be sure to document error messages and any error codes or memory locations that display on the screen.

Problem: General protection fault (GPF)

This can cause a program to fail, and in older versions of Windows, it would cause the entire OS to shut down and display a black screen. Today, these errors are uncommon and are usually related to the OS, running applications, and CPU. It is also possible that memory errors can cause a GPF, for example writing to a read-only portion of memory, or a conflict in a particular part of memory, but again, these are rare.

Problem: Stop error, aka BSOD or Blue Screen of Death:

This is a critical system error that causes the operating system to shut down. Most of the time, these are due to device driver errors (poor code), but they can be associated with a physical fault in memory. One example of this would be an nonmaskable interrupt (NMI). An NMI can interrupt the processor to gain its attention regarding nonrecoverable hardware errors, resulting in a BSOD. The BSOD usually dumps the contents of memory to a file (for later analysis) and restarts the computer. If you don't encounter another BSOD, it's probably not much to worry about. But if the BSOD happens repeatedly, you want to write down the information you see on the screen and cross-reference it to the Microsoft Support website at http:// support.microsoft.com

What are typical SDRAM clock rates? What are they called?

Typical SDRAM clock rates are 66 MHz, 100 MHz, and 133 MHz; the physical RAM sticks are referred to as PC66, PC100, and PC133, respectively.

Where is SRAM usually used?

You can find SRAM used as cache memory for CPUs, as buffers on the motherboard or within hard drives, and as temporary storage for LCD screens. Normally, SRAM is soldered directly to a printed circuit board (PCB) or integrated directly to a chip.

Memory Limitations for Windows Versions: a) General 32-bit versions b) 32-bit Windows 7 starter c) 64-bit Windows Vista/7 home basic d) Windows Vista/7 home premium e) XP f) higher versions of W7 g) higher versions of Vista

a) 4GB b) 2GB c) 8GB d) 16GB e) 128GB f) 192B g) 128GB

The data or instruction that the processor needs is usually found in one of three places:

cache, DRAM, or the hard drive

When might the computer underclock?

if you were for some reason to install two different types of RAM, for example one stick of DDR3-1333 and one stick of DDR3-1066 and the motherboard supported both; then the system would run at the lower speed of 1066. This is an example of underclocking; **However, in a dual-channel system, this could cause the system to fail, if the motherboard insists that the pair of modules be identical. Also, if you install the latest type of RAM that is supposed to be compatible with the motherboard, be prepared to flash the BIOS so that the system can recognize the new RAM, especially in dual-channel and tri-channel environments.

To store data permanently, where would you need to store data?

it would need to be written to a hard drive or other device, which is slower and less uniform in its storage and delivery of data.

What is another (easier way) to calculate data transfer rate?

multiply the megatransfers per second (MT/ s) by 8. Why 8? Because DDR sends 8 bytes per transfer. -Now solve for DDR-400. Equation: 400 MT/ s × 8 = 3,200 MB/ s.