RAM Chapter 1 part 4

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 RAM works, and how to install it properly.”

DRAM

DRAM DRAM (dynamic random access memory) is the most popular type of electronic memory Special type of semiconductor that stores ones and zeroes using microscopic capacitors and transistors Single chip can hold millions of these capacitor/transistor combinations 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.

Program Execution Program code is copied from your hard disk into RAM before it is executed 1011 0101 1001 0001 1011 0110 0001 1101 1101 1101 1100 0111 1001 1111 1100 1010

Organizing DRAM DRAM is considered the standard Low cost, high speed, and able to store data in a relatively small package Many varieties of DRAM DRAM stores programs and data in 8-bit (1-byte) chunks of memory Chips have historically been referenced with respect to their depth and width 1 MB x 4 256 K x 1

Organizing DRAM The depth and width are measured in units of bits Not easy to determine based on what’s written on chips The physical size and the internal organization of the chip are not directly related

Review: Memory Controller Chip The memory controller chip (MCC) device facilitates the flow of data from the RAM to the CPU Data is placed on the external data bus Width of data bus related to width or DRAM MCC

Practical DRAM 8086 used 16-bit data bus Much more expensive at the time At $12,000 per PC, would not have fueled the PC revolution Original 8088 chip used 8-bit data bus Market was ready for this Adapted to some commands needing 16 bits

Bus Review Address bus External data bus Frontside bus Backside bus This addresses the RAM Number of lines in address bus determines max RAM (32 lines = 4 GB, 36 lines = 64 GB) External data bus This is where data is placed once addressed MCC retrieves data from RAM on places on EDB Width of data bus dictates width of RAM Frontside bus Same as external data bus Backside bus Used to access cache For many students, “buses” tend to run together. Expect the question: “What’s the difference between the address bus, the external data bus, and the frontside bus? If you’re unable to coax the question out of them, look for an opportunity to provide the clarification. 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. External data bus This is where the data is passed back and forth between CPU and memory (via the MCC). Frontside bus 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.

DRAM Sticks

72-pin SIMMs A better solution was needed 72-pin SIMMs Modern CPUs have 64-bit external data buses 72-pin SIMMs have a notch in the middle Each 72-pin SIMM is 32 bits wide (two required)

Banking Combining the widths of DRAM to match the width of the external data bus is called banking The number of sticks that make up a bank depends on the chipset, which in turn depends on the CPU’s external data bus size EDB of 64 bits = 2 SIMMS 32 bits wide EDB of 64 bits = 1 DIMM 64 bits wide

Consumer RAM RAM has widths larger than bytes 8 bits wide = byte 16 bits wide = word 32 bits wide = double word However, still referred to in bytes 256 MB, 512 MB, 1 GB sticks

Essentials: Types of RAM CompTIA A+ Essentials Essentials: Types of RAM

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

SDRAM SDRAM (synchronous dynamic RAM) are tied to the system clocks Synchronized with system clock SDRAM is always a DIMM, but a DIMM isn’t always SDRAM Wide number of pins Small-outline DIMM (SO-DIIMM) used on laptops Faster than DRAMs 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

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.

DDR SDRAM Double Data Rate DDR SDRAM doubles the throughput of SDRAM 184-pin DIMM packages (desktops) 172-, 200-pin DIMM packages (laptops) Wide range of speeds Considered a standard today Dual slots are blue, third slot is black

DDR Speeds PC Speed Rating = Clock Speed DDR Speed Rating 100 MHz DDR200 PC1600 133 MHz DDR266 PC2100 166 MHz DDR333 PC2700 200 MHz DDR400 PC3200 217 MHz DDR433 PC3500 233 MHz DDR466 PC3700 250 MHz DDR500 PC4000 275 MHz DDR550 PC4400 300 MHz DDR600 PC4800 PC Speed Rating = Clock speed × 2 × 8

Dual-Channel Architecture Dual-channel architectures use two sticks of RAM together to increase throughput Similar to RAMBUS Works only if two sticks Dual slots often blue Third one often black 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.

DDR2 SDRAM DDR SDRAM doubles the throughput of SDRAM Doubled the clock, increasing buffering Does not speed up core RAM, but just the I/O 240-pin DIMM (not compatible with DDR)

DDR2 Speeds PC Speed Rating = Clock Speed DDR I/O Speed DDR Speed Rating PC Speed Rating 100 MHz 200 MHz DDR2-400 PC2-3200 133 MHz 266 MHz DDR2-533 PC2-4200 166 MHz 333 MHz DDR2-667 PC2-5300 400 MHz DDR2-800 PC2-6400 250 MHz 500 MHz DDR2-1000 PC2-8000 PC Speed Rating = Clock speed × 2 × 2 × 8

Double-Sided DIMMS Almost all sticks come as single-sided or double- sided Beware of double-sided sticks Some are thicker, which prevents populating all slots in some motherboards You motherboard may or may not be able to accept them.

Latency Latency Measure of how slow RAM may be. CL2 refers to low latency. Faster. It takes two clock cycles to get data. CL3 refers to high latency. Slower. It takes three clock cycles to get data. Often listed as CAS (column address strobe).

Parity and ECC Parity is a rudimentary method of checking the data to see if errors exist No error correction, just detection ECC (error correction code) is a special type of RAM used by high-end systems Major advance in error checking on DRAM Can also correct many errors RAM sticks of any size can use the ECC DRAM, but it is most common as 168-pin DIMMs A motherboard must 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.

Buffered/Registered DRAM Most motherboards support only four sticks of RAM More sticks present unique challenges To overcome output problems, sticks add a buffering chip Acts as intermediary between RAM and MCC

Working with RAM What’s wrong with this picture?

Working with RAM Avoid ESD damage Don’t touch pins or connectors directly RAM is highly susceptible to ESD damage.

Do You Need RAM? Two symptoms point to needing more RAM General system sluggishness, especially as more programs are opened Disk thrashing or excessive hard drive accessing, caused by excessive paging Note: Disk thrashing can also be caused by disk fragmentation. How do know if your disk is thrashing? Observe the LED at work Use FreeMeter (www.tiler.com/freemeter)

Page File Data can be moved between physical RAM and virtual RAM Data swapped in 64-K page blocks Too much too often causes disk thrashing Physical RAM Disk drive Game OS Note that this is a simplistic representation. Entire programs aren’t swapped back and forth between memory and the hard drive. Instead, 64-K pages are swapped based on what the system predicts won’t be needed soon. The name page file is derived from the 64-K “pages.” Word Browser E-mail

System RAM Recommendations Operating System Reasonable Minimum Solid Performance Power User Windows 2000 128 MB 256 MB 512 MB Windows XP 1 GB Windows Vista 2 GB Actual minimum requirements are much lower Usually leads to slower computer and unhappy user

Determining Current RAM My Computer Properties Windows key- Pause/Break key Task Manager Ctrl-Shift-Esc

Getting the Right RAM Identify capacity Identify empty slots What can the motherboard handle (look at the manual) Identify empty slots If all slots filled, you’ll have to pull some out For example, pull out 256-MB sticks to add 512-MB sticks CPU-Z is a great tool to determine what you have Also shows latency

Mixing and Matching Mixing DRAM speeds can cause the system to lock up, leading to data corruption You can use faster DRAM than the motherboard recommends, but you 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.

Installing DIMMs Swing the side tabs away from upright. Push the DIMM down somewhat hard. The two tabs should move back into place

Memory Details Signal presence detect (SPD) The RAM count Reports the size, speed, data width, and voltage of the installed RAM to the BIOS Can be read from BIOS CPU-Z shows SPD data The RAM count Part of Power On Self Test Counts addressable RAM and reports it Remember the subtle differences between counting in binary and decimal 512 MB does not equal 512 million exactly.

Installing SO-DIMMs in Laptops Make sure the system is off No AC connection Remove all batteries Remove the panel or lift the keyboard Slide the pins into position and then snap the SO-DIMM down into the retaining clips 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.

IT Technician CompTIA A+ Technician Troubleshooting RAM

Memory Errors Appear as Real memory errors Phantom errors Parity errors, ECC error messages, system lockups, page faults, and BSoD Real memory errors “Parity error at xxxxx” If xxxxx is consistently the same, you have a bad RAM stick Phantom errors Random memory addresses Due to power issues, dust, heat

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

Testing RAM Hardware RAM testing devices can be used to troubleshoot errors An economical option is to replace the existing sticks with new ones Memtest32 is a freeware tool that can be used to test RAM

Beyond A+ To get the graphics response needed, games need powerful video cards and video RAM Watch video cards to see where RAM is headed