A+ Guide to Hardware, 4e. Chapter 6 Upgrading Memory

Transcription

1 A+ Guide to Hardware, 4e Chapter 6 Upgrading Memory

2 Objectives Learn about the different kinds of physical memory and how they work Learn how to upgrade memory Learn how to troubleshoot problems with memory A+ Guide to Hardware, 4e 2

3 Introduction Memory technologies have evolved rapidly Study development to grasp current technology Memory-related tasks performed by a PC technician Upgrading memory Adding more memory to a system Troubleshooting problems with memory A+ Guide to Hardware, 4e 3

4 RAM Technologies RAM (random access memory) Holds data and instructions used by CPU Volatile (data does not persist after PC is turned off) ROM (read-only memory) In firmware on motherboard; e.g., ROM BIOS Non-volatile (retains data after PC is turned off) Reviewing other salient features of RAM RAM is stored in modules: DIMMs, RIMMs, SIMMs Types: static RAM (SRAM) and dynamic RAM (DRAM) Memory cache is made up of SRAM (it is faster) A+ Guide to Hardware, 4e 4

5 Figure 6-1 DRAM on most motherboards today is stored on DIMMs A+ Guide to Hardware, 4e 5

6 RAM Technologies (continued) Differences among DIMM, RIMM, and SIMM modules Width of the data path each module accommodates The way data moves from system bus to the module Older DRAM worked asynchronously with system bus Newer DRAM works synchronously with system bus Retrieves data faster as it keeps time with system clock Goal of each new technology Increase overall throughput while retaining accuracy A+ Guide to Hardware, 4e 6

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8 SIMM Technologies SIMMS have a 32-bit data path Speeds (access times): 60, 70, 80 nanoseconds (ns) Smaller number indicates greater speed Components making up the access time Processor requests the data Memory controller locates data on the SIMM Data is placed on the memory bus The processor reads the data off the bus Memory controller refreshes memory chip on SIMM A+ Guide to Hardware, 4e 8

9 DIMM Technologies DIMM (dual inline memory module) Has independent pins on opposite sides of module Can have memory chips on one or two sides Has 168, 184, or 240 pins on edge connector Has a 64-bit data path and holds 8 MB - 2 GB RAM Synchronous DRAM (SDRAM) Has two notches, and uses 168 pins DDR (Double Data Rate) and DDR2 DIMM DDR SDRAM runs 2 x faster than regular SDRAM DDR2 SDRAM is faster than DDR, uses less power A+ Guide to Hardware, 4e 9

10 DDR Verses DDR2 DDR memories are officially found in 266 MHz, 333 MHz and 400 MHz versions, DDR2 memories are found in 400, 533, 667and 800 MHz + versions. Both types transfer two data per clock cycle. DDR memories are fed with 2.5 V while DDR2 memories are fed with 1.8 V. A+ Guide to Hardware, 4e 10

11 DDR Verses DDR2 On DDR memories the resistive termination necessary for making the memory work is located on the motherboard, DDR2: this circuit is located inside the memory chip. This is one of the reasons why it is not possible to install DDR2 memories on DDR sockets and vice-versa. DDR modules have 184 contacts DDR2 modules have 240 contacts. Internally the controller inside DDR memories works preloading two data bits from the storage area (task known as prefetch ) while the controller inside DDR2 memories works loading four bits in advance. A+ Guide to Hardware, 4e 11

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13 DDR2: Latencies On DDR memories the CAS Latency (CL) parameter which is the time the memory delays delivering a requested data, can be of 2, 2.5 or 3 clock cycles. On DDR2 memories CL can be of 3, 4 or 5 clock cycles. On DDR2 memories, depending on the chip, there is an additional latency (AL) of 0, 1, 2, 3, 4 or 5 clock cycles. So in a DDR2 memory with CL4 and AL1 the latency is 5. A+ Guide to Hardware, 4e 13

14 LAPTOP - SODIMM SODIMM is Small Outline DIMM. SODIMM is a smaller DIMM which is designed for use in notebook computers and other spacerestricted environments. SODIMM is sometimes written as SO-DIMM. A+ Guide to Hardware, 4e 14

15 Thee types of SODIMM s Contact Count Data Bus Width A+ Guide to Hardware, 4e 15

16 CAS When selecting a RAM card, the lower the CAS latency (given the same clock speed), the better the system performs. Current DDR RAM should have a CAS latency of about 3, or optimally 2 (and more recently 1.5). DDR2 RAM can have latencies ranging from 2.5 to 6. A+ Guide to Hardware, 4e 16

17 DDR2: Latencies DDR2 memories work with higher latencies than DDR memories. In other words, they delay more clock cycles to deliver a requested data. Does this mean that DDR2 memories are slower than DDR memories? Not necessarily. They delay more clock cycles, but not necessarily more time. A+ Guide to Hardware, 4e 17

18 If we compare a DDR memory to a DDR2 memory running under the same clock, the one with the lower latency will be the fastest. Thus, if you have a DDR400 CL3 memory and a DDR2-400 CL4 memory, your DDR400 will be faster. Keep in mind that DDR2 memories have an additional parameter called AL (additional latency), which must be added to their nominal latency (CL) in order to get the total latency. When comparing memories with different speeds, you need to consider the clock in your math. A+ Guide to Hardware, 4e 18

19 On a DDR400 CL3 memory, this 3 means that the memory delays three clock cycles to start delivering the requested data. Since this memory runs at 200 MHz, each clock tick measures 5 ns (T= 1/f). Thus its latency is 15 ns. A+ Guide to Hardware, 4e 19

20 Now on a DDR2-533 CL3 AL0 memory, this 3 also means that the memory delays three clock cycles to start delivering the request data, but since this memory runs at 266 MHz, each clock tick measures 3.75 ns, so its latency is of ns, making this memory faster to data delivery than our DDR400 CL3 memory. So a DDR2-533 CL4 and AL0 memory has the same latency as a DDR400 CL3. Notice that we are assuming the additional latency as zero, or we would need to take it into account, i.e., a DDR2 CL3 AL1 memory has in reality a latency of four clock cycles. A+ Guide to Hardware, 4e 20

21 Some manufacturers announce their memory module latencies thru a series of four number, like or or The latency we ve been talking about (CL) is the first number on the sequence. A+ Guide to Hardware, 4e 21

22 How To Read CAS RAM manufacturers typically list the recommended timing for their RAM as a series of four integers separated by dashes (e.g or or and so on). These four integers refer to the following settings, CL - TRCD - TRP - TRAS. A+ Guide to Hardware, 4e 22

23 CL CL = CAS Latency time: The time it takes between a command having been sent to the memory and when it begins to reply to it. It is the time it takes between the processor asking for some data from the memory and the memory returning it. A+ Guide to Hardware, 4e 23

24 TRCD TRCD = DRAM RAS# to CAS# Delay: The number of clock cycles performed between activating the Row Access Strobe and the Column Access Strobe. This parameter relates to the time it takes to access stored data. A+ Guide to Hardware, 4e 24

25 TRP TRP = DRAM RAS# Precharge: The amount of time between the 'precharge' command and the 'active' command. The 'precharge' command closes memory that was accessed and the 'active' command signifies that a new read/write cycle can begin. A+ Guide to Hardware, 4e 25

26 TRAS TRAS = Active to Precharge delay: The total time that will elapse between an active state and precharge state. A+ Guide to Hardware, 4e 26

27 What the heck does it mean? The lower the CAS latency (given the same clock speed), the less time it takes to fetch data from it. So in novice terms, 'the lower CAS latency, the better it is.' A+ Guide to Hardware, 4e 27

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30 False DDR3 SDRAM DDR3 is part of the SDRAM family of technologies and is one of the many DRAM (dynamic random access memory) implementations. DDR3 SDRAM is an improvement over its predecessor, DDR2 SDRAM. A+ Guide to Hardware, 4e 30

31 DDR3 SDRAM The primary benefit of DDR3 is the ability to transfer I/O data at eight times the data rate of the memory cells it contains, thus enabling higher bus rates and higher peak rates than earlier memory technologies. However, there is no corresponding reduction in latency, which is therefore proportionally higher. DDR3 standard allows for chip capacities of 512 megabits to 8 gigabits, effectively enabling a maximum memory module size of 16 gigabytes A+ Guide to Hardware, 4e 31

32 DDR3 SDRAM DDR3 memory provides a reduction in power consumption of 30% compared to DDR2 modules due to DDR3's 1.5 V supply voltage compared to DDR2's 1.8 V or DDR's 2.5 V. The 1.5 V supply voltage works well with the 90 nanometer fabrication technology used in the original DDR3 chips. A+ Guide to Hardware, 4e 32

33 Error Checking and Parity Bank: smallest group of working memory chips Example: eight memory chips used in 8-bit data path Parity: error-checking based on an extra (ninth) bit Odd parity: parity bit is set to make odd number of ones Even parity: parity bit set to make even number of ones Parity error: number of bits conflicts with parity used Example: odd number of bits read in even parity system ECC (error-correcting code) Detects and corrects an error in a single bit Application: ECC makes 64-bit DIMM a 72-bit module A+ Guide to Hardware, 4e 33

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35 DDR3 evolution from DDR2 SDRAM DDR3 SDRAMs are following the same path that previous generations of DDR & SDRAMs have, and are thus slated to provide higher data rates than DDR2 SDRAMs. This new architecture comes with enhancements that help with the design of the physical layer, system, and controller interface. Architectural changes were required to enable external controllers to communicate at these higher rates and the DDR3 memory device to provide I/O throughput up to 1,600 Mbps. A+ Guide to Hardware, 4e 35

36 DDR3 evolution from DDR2 SDRAM The performance limiter for DRAMs has been and continues to be the internal memory array. Increasing external data rates to keep up with performance demands is difficult to scale at the internal memory array level. The DDR2 architecture uses a 4n prefetch scheme that enables four words to be accessed in the internal memory array for every command. This was not sufficient to keep up with higher external data rates, however, and an 8n prefetch was introduced with DDR3. A+ Guide to Hardware, 4e 36

37 DDR3 evolution from DDR2 SDRAM Because calibration for improved timing is essential with higher data rates, the DDR3 architecture has introduced two new features. MPR & JEDEC A+ Guide to Hardware, 4e 37

38 DDR3 evolution from DDR2 SDRAM MPR For read calibration during initialization, a multipurpose register (MPR) provides the means for calibrating the read operation at the controller side, with a data pattern sent out from this register rather than the memory array. This feature can be useful when the memory array is not used to generate the data read pattern. A+ Guide to Hardware, 4e 38

39 DDR3 evolution from DDR2 SDRAM JEDEC For applications requiring the use of DDR3 DIMMs, the JEDEC standard prescribes the fly-by topology. This fly-by topology is different than DDR2 DIMMs, where the signals are routed to arrive at the same time for all of the memory components on the DIMM. In the case of the fly-by topology, signals are routed to each component in serial-like fashion and flight times to memory devices are skewed. This improves signal integrity from the reduction of A+ Guide stubs to Hardware, but requires 4e additional complexity for the 39

40 DDR3 evolution from DDR2 SDRAM JEDEC In the case of the fly-by topology, signals are routed to each component in serial-like fashion and flight times to memory devices are skewed. This improves signal integrity from the reduction of stubs but requires additional complexity for the controller. A+ Guide to Hardware, 4e 40

41 DDR3 - SPEEDS DDR ,400 MB/s DDR ,533 MB/s DDR ,667 MB/s DDR ,800 MB/s A+ Guide to Hardware, 4e 41

42 DDR3 A+ Guide to Hardware, 4e 42

43 CAS Latency and RAS Latency Two ways of measuring speed CAS stands for column access strobe RAS stands for row access strobe Both types measure read/write clock cycles Two or three clock cycles per column or row of data CAS latency is used more than RAS latency A+ Guide to Hardware, 4e 43

44 Tin or Gold Leads Connectors inside memory slots are tin or gold Edge connectors on memory modules follow suit Tin leads should match tin connectors Gold leads should match gold connectors Prevents corrosive chemical reactions between metals A+ Guide to Hardware, 4e 44

45 Memory Speeds Measures: ns, MHz, PC rating, CAS or RAS Latency Example: SDRAM, DDR, and RIMM measured in MHz PC rating: total bandwidth between module and CPU Example: 200 MHz x 8 bytes = 1600 MB/sec = PC1600 Factors to consider when looking at overall speed: How much RAM is installed and the technology used Speed of memory in ns, MHz, or PC rating ECC/parity or non-ecc/nonparity CL or RL rating Use of dual channeling A+ Guide to Hardware, 4e 45

46 How to Upgrade Memory The basic technique: add more RAM modules Problems solved with new memory: Slow performance Applications refusing to load An unstable system Note empty memory slots on most new computers Accommodate new DIMM or RIMM A+ Guide to Hardware, 4e 46

47 How Much and What Kind of Memory to Buy Questions to ask before performing an upgrade: How much memory do I need? How much RAM is currently installed in my system? How many memory modules are currently installed? What kind of memory modules are currently installed? How much memory can I fit on my motherboard? What kind of memory can I fit on my motherboard? How do I select and purchase the right memory? Refer to system utilities to determine capacity Motherboard documentation guides choice of add-ons A+ Guide to Hardware, 4e 47

48 Figure 6-14 How three DIMM slots can use four 64-bit memory banks supported by a motherboard chipset A+ Guide to Hardware, 4e 48

49 Figure 6-16 Selecting memory off the Crucial Web site A+ Guide to Hardware, 4e 49

50 Figure 6-18 Installing a SIMM module A+ Guide to Hardware, 4e 50

51 Figure 6-19 Install RIMM modules in banks beginning with bank 0 A+ Guide to Hardware, 4e 51

52 Figure 6-20 Installing a DIMM module A+ Guide to Hardware, 4e 52

53 Troubleshooting Memory Common problems: Boot failure A system that hangs, freezes, or becomes unstable Intermittent application errors General Protection Fault (GPF) errors Caused by memory errors in Windows A+ Guide to Hardware, 4e 53

54 Upgrade Problems Dealing with unrecognized add-on or error message Remove and reinstall the module Check for the suitability of the module for the board Ensure that the module is the correct size Remove the module and check for error message Test the module in another socket Clean the module edge connectors Try flashing BIOS A+ Guide to Hardware, 4e 54

55 Recurring Problems Symptoms of an unreliable memory: The system locks up Error messages about illegal operations often display General Protection Faults occur during normal operation Some troubleshooting tasks Run updated antivirus software to check for viruses Replace memory modules one at a time Try uninstalling the new hardware Test, reseat, or replace RAM Verify that virtual memory settings are optimized A+ Guide to Hardware, 4e 55

56 Summary RAM categories: static RAM (SRAM), dynamic RAM (DRAM) Modules used to store DRAM: SIMM, DIMM, RIMM Synchronous DRAM (SDRAM): moves to the beat of the system clock Simple parity checks identify one corrupted bit Error correcting code (ECC) detects and corrects one flipped bit A+ Guide to Hardware, 4e 56

57 Summary (continued) Memory speeds are measured in ns, MHz, PC rating, CAS or RAS Latency When upgrading memory, use the type, size, and speed the motherboard supports New modules should match those already installed Install new modules by inserting them into the appropriate slots When troubleshooting, first try the simple technique of reseating the module A+ Guide to Hardware, 4e 57