A+ Certification Guide Chapter 5 Random Access Memory
Chapter 5 Objectives 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.
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.
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
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
RAM Types Illustrated
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.
Know These Before Taking Exam RAM Type Pins Common Type and Speed Defining Characteristic SDRAM 168 PC133 = 133Mhz This original version of SDRAM is rarely used on new computers and has given way to DDR. DDR 184 PC3200 = 400MHz/ 3200MB/s Double the transfers per clock cycle compared to regular SDRAM. DDR2 240 DDR2-800 (PC2-6400) = 800MHz/ 6400MB/s External data bus speed (I/O bus clock) is 2 x DDR SDRAM. Rambus 184 and 232 PC800 = 1600MB/s Not used in new computers, but you still might see existing systems using RAMBUS memory modules.
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.
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.
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.
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
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. 1. Check to see if the locking tabs are swiveled out to open position. 2. Line up module to accommodate the notch that ensures that the module is being inserted in the right direction. 3. 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.
Installing Memory Channel A (Blue) should be installed (in pairs) before Channel B slots are used.
Installing Memory
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.
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.
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.
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.
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?
Chapter 5 Summary 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