A+ Certification Guide

1. A+ Certification Guide Chapter 5 Random Access Memory

2. Chapter 5Objectives • RAM Basics: • Describe what RAM does, how it works, and how it relates to the system. • RAM Types: • Describe types of RAM available, including SDRAM, DDR, and Rambus. • Operational Characteristics: • Describe the features of memory modules and types of memory like ECC, EDO, registered, and unbuffered. • Installing Memory Modules: • Demonstrate how to install SIMMs and DIMMs properly. • Troubleshooting Memory: • Describe issues with RAM due to incompatible memory speeds and types. • Preventative Maintenance for Memory: • Describe measures to take to keep memory modules clean and protected.

3. Random Access Memory • Random access: • Means that memory addresses are dynamically allocated. • Different from ROM in which memory addresses are pre-assigned to specifically coded functions. • What role does RAM play? • Provides CPU with data to process: • Keyboard entries are sent to RAM addresses. • Hard drive programs are sent to RAM addresses. • Network data (web pages) are sent to RAM addresses. • RAM is faster than other storage, such as hard drives and USB memory. • Installing more RAM is often the easiest way to improve system performance without investing in a new system.

4. RAM Specifications to Know(Before You Buy) • Module type: • Number of pins (240,184, and 168) and placement • Number of RAM slots available for modules • Chip type: • SDRAM, DDR, RDRAM • Speed: • Needs to match up as multiple of motherboard front-side bus speed • Measured in nanoseconds or in throughput. • Error checking: • Optional, purchased with database servers • Number of modules needed per bank • Dual channel or triple channel configuration

5. RAM Types • SRAM = Static Random Access Memory: • Also known as L1, L2, and L3 cache memory • Does not require a memory refresh • Used with CPU to store frequently accessed data routines • Fast but expensive • Not generally upgradeable • SDRAM = Synchronous Dynamic Random Access Memory • DDR = Double Data Rate • DDR2 = Double Data Rate (enhanced) • Rambus

6. RAM Types Illustrated

7. RAM Types (Continued) • SDRAM = Synchronous Dynamic Random Access Memory: • PCs made before 2000 commonly use this. • Rated by bus speed: • 266Mhz bus uses PC266 SDRAM. • DDR = Double Data Rate SDRAM: • Rated by throughput speed in MBps. • PC2700 means it can deliver 2,700MBps. • DDR2 = Double Data Rate SDRAM (next-generation DDR): • Twice the speed of DDR. • PC2 prefix number designates a module as DDR2. • Rambus (RDRAM) and RIMM: • Not in common use.

8. Know These Before Taking Exam

9. Operational Characteristics • Memory modules are classified in various ways: • The amount of memory (in bits) found on the module • The differences between parity and nonparity memory • The differences between ECC and non-ECC memory • The differences between registered and unbuffered memory • The differences between single-sided and double-sided memory The following slides deal with these operational characteristics.

10. Memory Module Characteristics • Single Inline Memory Module (SIMM): • Single row of 30- or 72-edge connectors. Single refers to both sides of the module having the same pinout. • Single Inline Pin Package (SIPP): • Variation on the 30-pin SIMM. • Dual Inline Memory Module (DIMM): • 168-pin, 184-pin, and 240-pin versions. Dual refers to each side of the module having a different pinout. • Small Outline DIMM (SODIMM): • A compact version of the standard DIMM module, for use in notebook computers. • Rambus RDRAM Module or RIMM • A memory module using Direct Rambus memory (RDRAM) chips.

11. Operational Characteristics • Memory module width: • 8 bits = 1 byte. • Memory is sold as measured in bytes: • Megabyte • Gigabyte • Memory width refers to the 32-bit or 64-bit path: • Usually matches processor/motherboard path. • A memory module is the same as a memory “bank”: • A bank of memory is one module installed in a single memory slot. • Slots must be compatible with memory module: • 72-pin slot versus 168- or 184-pin slot. • Multiple banks usually require matched pairs of memory modules.

12. Operational Characteristics • Parity and nonparity memory: • Error checking memory costs more. • Small performance decrease. • Two types: • Parity checking: • Use of a parity bit to compute a value that must match another value to validate a data set • ECC (error-correcting code): • Memory that both finds and corrects errors • Typically employed on servers • Registered versus unbuffered: • Buffered memory (registered): • Enables system stability when large memory banks are used

13. Installing Memory Modules Preinstall precaution: Importance of ESD protection: • Memory can be damaged, and the damage may not show up for weeks. • ESD strap must be attached to a ground or bare metal portion of the chassis. • Hold memory modules by the side edges without touching either the pins or the memory chips. • Check to see if the locking tabs are swiveled out to open position. • Line up module to accommodate the “notch” that ensures that the module is being inserted in the right direction. • Push module straight down into position: • A slight rocking motion from end to end helps seat stubborn modules into the slot. • Engaging the locks requires extra firmness to force the locks to close into the notches on the sides of the module.

14. Installing Memory Channel A (Blue) should be installed (in pairs) before Channel B slots are used.

15. Installing Memory

16. Troubleshooting Memory Sources of problems: • Incompatible module. • Overclocking/overheating. • Incompatible metals in slots and on pins: • Causes corrosion. • Need to be cleaned periodically. • Mismatched RAM speeds: • Measured in nanoseconds. • Lower numbers mean faster access times. • Newer systems generally adjust to slowest module.

17. Determining if Cache RAM Has a Memory Problem Cache RAM holds a copy of the information in main memory. Errors in cache RAM can appear to be errors in system RAM. Procedure to determine if cache RAM is the cause of a memory problem: • Disable L2 cache first. • If the memory problem goes away, determine where L2 cache is located (processor or motherboard). • If the motherboard uses removable cache module, replace it. • If the motherboard uses nonremovable cache chips, replace the motherboard. • If L2 cache is built in to the processor, replace the processor. • If the system runs normally, the replacement is successful. • If the problem persists after replacing the component containing cache RAM, return the original component(s) to the system. • Disable L1 cache. • If the system runs normally, replace the CPU and retest. • If system runs normally after replacement, the L1 cache was faulty.

18. Troubleshooting Memory RAM-Sizing Errors at Bootup • Note the memory count reached onscreen when the memory error is detected. • Check the motherboard documentation to see which modules must be installed first. • Change one module at a time, starting with the one you think is defective, until the error goes away. • Disable cache RAM in the BIOS setup when testing memory.

19. Preventative Maintenance for Memory • Keep the surfaces of the modules clean: • Use compressed air or a data-rated vacuum cleaner to remove dust. • Use the recommended voltage level for the memory installed if your system's BIOS setup permits voltage adjustments. • Install additional case fans over or behind the location of memory modules to pull hot air out of the system. • Keep air intake vents in the front of the system clean. • Replace any defective cooling fans.

20. What Have You Learned? • What kind of memory would be useful to verify data integrity? • How many memory modules are required for a CPU with a 64-bit bus width? • What kind of memory module is typically used in L1/L2 cache and does not require a constant refresh? • In what speed standard is memory measured?

21. Chapter 5Summary • Describe what RAM does, how it works, and how it relates to the system. • Describe types of RAM available, including SDRAM, DDR, and Rambus. • Describe the features of memory modules and types of memory like ECC, EDO, registered, and unbuffered. • Demonstrate how to install SIMMs and DIMMs properly. • Describe issues with RAM due to incompatible memory speeds and types. • Describe measures to take to keep memory modules clean and protected. Next Lesson: Chapter 6