PC Maintenance: PC Maintenance: Preparing for A+ Preparing for A+

CertificationCertificationChapter 6: MemoryChapter 6: Memory

Chapter 6 ObjectivesChapter 6 Objectives Differentiate between types of memoryDifferentiate between types of memory Understand how memory holds dataUnderstand how memory holds data Identify physical types of RAMIdentify physical types of RAM Explain how an OS uses RAMExplain how an OS uses RAM Differentiate between conventional, upper, Differentiate between conventional, upper,

expanded and extended memoryexpanded and extended memory Get RAM usage information in an OSGet RAM usage information in an OS

Types of MemoryTypes of Memory Read-Only Memory (ROM)Read-Only Memory (ROM) Random Access Memory (RAM)Random Access Memory (RAM)

Dynamic RAM (DRAM)Dynamic RAM (DRAM) Static RAM (SRAM)Static RAM (SRAM)

Read-Only Memory (ROM)Read-Only Memory (ROM) Non-volatileNon-volatile Types of ROM chips:Types of ROM chips:

Programmable ROM (PROM)Programmable ROM (PROM) Erasable Programmable ROM (EPROM)Erasable Programmable ROM (EPROM) Electrically Erasable Programmable ROM Electrically Erasable Programmable ROM

(EEPROM)(EEPROM)

Random Access Memory (RAM)Random Access Memory (RAM)

SRAMSRAM Non-volatileNon-volatile Examples: L1 and L2 cachesExamples: L1 and L2 caches

DRAMDRAM VolatileVolatile Examples: system RAM, video RAMExamples: system RAM, video RAM

How RAM Stores DataHow RAM Stores Data Each chip has a grid of on/off capacitorsEach chip has a grid of on/off capacitors Each RAM chip’s grid has a width and Each RAM chip’s grid has a width and

depth, like a spreadsheetdepth, like a spreadsheet A A bankbank is a group of chips with a collective is a group of chips with a collective

width matching the buswidth matching the bus

11 00 11 11 00 00 11 1100 11 11 11 00 11 11 0011 11 00 00 11 11 00 0011 00 11 00 11 00 11 11

How RAM Stores DataHow RAM Stores Data Multiple chips combine their widths to Multiple chips combine their widths to

match the width of the busmatch the width of the bus

What is a Stick of RAM?What is a Stick of RAM? StickStick: A SIMM or DIMM that holds a group : A SIMM or DIMM that holds a group

of chipsof chips

SIMMsSIMMs Single Inline Single Inline

Memory Modules Memory Modules (SIMMs)(SIMMs) 30-pin (8-bit)30-pin (8-bit) 72-pin (32-bit)72-pin (32-bit) Both are now Both are now

obsoleteobsolete

DIMMsDIMMs Dual Inline Memory Modules (DIMMs)Dual Inline Memory Modules (DIMMs)

168-pin (64-bit)168-pin (64-bit) SDRAM synchronized with system busSDRAM synchronized with system bus DDR SDRAM is double the system bus speedDDR SDRAM is double the system bus speed

RIMMsRIMMs Rambus Inline Memory Modules (RIMMs)Rambus Inline Memory Modules (RIMMs)

184-pin (64-bit)184-pin (64-bit) Faster than DIMMsFaster than DIMMs Up to 8X or more of the system bus speedUp to 8X or more of the system bus speed More expensive, less popularMore expensive, less popular Waning in popularityWaning in popularity

How Many Sticks Per Bank?How Many Sticks Per Bank? SIMMsSIMMs

Four 30-pin SIMMs make up a 32-bit bankFour 30-pin SIMMs make up a 32-bit bank One 72-pin SIMM makes up a 32-bit bankOne 72-pin SIMM makes up a 32-bit bank Two 72-pin SIMMs make up a 64-bit bankTwo 72-pin SIMMs make up a 64-bit bank

DIMMs and RIMMsDIMMs and RIMMs One 168-pin DIMM makes up a 64-bit bankOne 168-pin DIMM makes up a 64-bit bank One 184-pin RIMM makes up a 64-bit bankOne 184-pin RIMM makes up a 64-bit bank

RAM ParityRAM Parity One-bit parity chip for error correctionOne-bit parity chip for error correction Primarily found on 72-pin SIMMs, now mostly Primarily found on 72-pin SIMMs, now mostly

obsoleteobsolete

Later variant Later variant was Error Code was Error Code Correction Correction (ECC) RAM(ECC) RAM

RAM SpeedsRAM Speeds Fast Page Mode (FPM)Fast Page Mode (FPM)

Speed measured in nanoseconds of delaySpeed measured in nanoseconds of delay Lower number is betterLower number is better

Synchronous Dynamic RAM (SDRAM)Synchronous Dynamic RAM (SDRAM) Speed synchronized with system busSpeed synchronized with system bus Measured in MHzMeasured in MHz Higher number is betterHigher number is better

Selecting RAMSelecting RAM Physical size of the stick (number of pins)Physical size of the stick (number of pins) CapacityCapacity SpeedSpeed Refresh technologyRefresh technology ParityParity

Understanding Memory Understanding Memory AddressesAddresses

A logically assigned location in RAMA logically assigned location in RAM Described using hexadecimalDescribed using hexadecimal Width of address bus determines available Width of address bus determines available

addressesaddresses

The First MegabyteThe First Megabyte 640K Conventional Memory640K Conventional Memory

Running Applications in Real-ModeRunning Applications in Real-Mode

360K Upper 360K Upper MemoryMemory Reserved Reserved

for system for system useuse

Expanded MemoryExpanded Memory Developed for 80286 systemsDeveloped for 80286 systems EMS (Expanded Memory Specification)EMS (Expanded Memory Specification) Also called LIM memory (Lotus-Intel-Also called LIM memory (Lotus-Intel-

Microsoft)Microsoft)

Expanded MemoryExpanded Memory Swaps data into and out of a 64K page Swaps data into and out of a 64K page

frame in upper memoryframe in upper memory

Extended MemoryExtended Memory Originally developed for 80386 systemsOriginally developed for 80386 systems Can be accessed directly by protected-Can be accessed directly by protected-

mode applicationsmode applications HIMEM.SYS required HIMEM.SYS required XMS (Extended Memory Specification) is XMS (Extended Memory Specification) is

the standardthe standard Still in use todayStill in use today

DOS Memory UsageDOS Memory Usage Use the MEM commandUse the MEM command

DOS Memory UsageDOS Memory Usage

The The MEM /C | MEM /C | MORE MORE command command provides provides more more informationinformation

Windows Memory UsageWindows Memory Usage Mostly automaticMostly automatic Check amount of Check amount of

RAM in System RAM in System PropertiesProperties

System InformationSystem Information

Virtual MemoryVirtual Memory

Windows Windows automatically automatically controls virtual controls virtual memory, but memory, but settings can be settings can be overriddenoverridden