Managing Memory

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Chapter 6

• Managing Memory

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You Will Learn

• About the different kinds of physical memory and
  how they work
• How to upgrade and troubleshoot memory
• How DOS and Windows 9x view and manage memory

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Physical Memory Review

• Temporarily holds data and instructions as CPU
  processes them
• Two categories
• ROM
• Retains its data when PC is turned off
• Stores data on chips socketed or soldered to
  circuit boards
• RAM
• Loses its data when PC is turned off
• Housed on SIMMs, DIMMs, or RIMMs

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ROM on the Motherboard

• Consists of memory chips that contain programs
  (ROM BIOS) that are acid-etched into the chips
  and cannot be changed
• EPROM (erasable programmable ROM) and EEPROM
  (electrically erasable programmable ROM) chips
  can be reprogrammed

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ROM on the Motherboard
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RAM on the Motherboard

• Serves as main memory
• Provides a memory cache
• Two categories
• Dynamic RAM (DRAM)
• Needs to be refreshed by the memory controller
• Usually stored on DIMMs, less commonly on RIMMs
• Static RAM (SRAM)

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DRAM Storage
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SRAM Storage
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SRAM and DRAM
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Static RAM Technologies

• Provide faster access than DRAM because data does
  not need to be constantly rewritten to SRAM
• SRAM chips are made of transistors that can hold
  a charge
• DRAM chips are made of capacitors that must be
  recharged
• Due to expense of SRAM chips, most computers have
  a little SRAM and a lot of DRAM

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How SRAM Is Used in Different Memory Caches
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How Memory Caching Works
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Different Types of SRAM

• Synchronous SRAM
• Burst SRAM
• Pipelined burst SRAM
• Asynchronous SRAM

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Dynamic RAM Technologies

• Always stored in SIMMs, DIMMs, or RIMM modules
• Major differences among modules
• Width of the data path that each accommodates
• The way data moves from system bus to module
• Goal is to increase overall throughput while
  retaining accuracy

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Examples of Memory Modules
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Summary of DRAM Technologies
continued
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Summary of DRAM Technologies
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SIMM Technologies

• Rated by speed, measured in nanoseconds (ns)
• Can use either EDO or FPM technology

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DIMM Technologies

• Rated by speed and amount of memory they hold
• Use either BEDO or synchronous SDRAM (SDRAM)
• Variations of SDRAM
• Regular SDRAM
• DDR SDRAM (SDRAM II)
• SyncLink (SLDRAM)

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DIMM Technologies
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RIMM Technologies

• Use a narrower data path than SIMMs or DIMMs in
  order to provide faster data transmission
• Data moves from the system bus sequentially
  through each RIMM module

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RIMM Technologies
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Parity and Error Checking

• Parity
• Error-checking procedure in which every byte has
  either an even or an odd number of ones
• Every byte occupies nine rather than eight bits
• ECC (Error-Correcting Code)
• New method of error checking that not only
  detects but also corrects an error in a single bit

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Parity
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Upgrading Memory

• Use type, size, density, and speed of memory that
  motherboard supports
• Match memory modules already installed
• Guidelines for selecting high-quality chips
• Tin or gold leads
• Remanufactured and used modules
• Re-marked chips

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How Much and What Kind of Memory to Buy

• How much memory do I have/need?
• How many memory slots on motherboard? What
  type/size of memory do they support?
• How much additional memory is cost-effective?
• Match memory modules to the motherboard

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How Much Memory Can Fit on the Motherboard?
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Example of an RDRAM Memory Configuration
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Installing Memory

• Protect chips against static electricity
• Use a ground bracelet
• Turn off power and remove cover to case
• Handle memory modules with care

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Installing a SIMM Module
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Installing a DIMM Module
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Installing a DIMM Module
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Troubleshooting Memory

• What if the computer does not recognize new
  SIMMs, DIMMs, or RIMMs, or if memory error
  messages occur?
• What if the system locks up or you regularly
  receive error messages about illegal operations,
  and General Protection Faults occur during normal
  operation and you have not just upgraded memory?

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How DOS Addresses Physical Memory

• Assigning addresses to both RAM and ROM
• Occurs during booting (sometimes called memory
  mapping)
• Is done by every OS

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Areas of the Memory Map

• Logical divisions determined by memory addresses
  rather than physical location
• Conventional (base) First 640K
• Upper 640K up to 1024K
• Extended Above 1024K
• First 64K are called high memory area (HMA)

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Areas of the Memory Map
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Memory Map of Upper Memory
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DOS Utilities That Manage Memory

• Himem.sys
• Device driver for all memory above 640K
• Allows DOS to access memory addresses above1 MB
• Emm386.exe
• Contains software that loads device drivers and
  other programs into upper memory

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Using Himem.sys
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Using Emm386.exe
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Creating and Using Upper Memory Blocks
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Chapter Summary

• How DOS and Windows 9x manage memory
• Memory
• Required for a system to work
• Stored on microchips, which are often stored on
  memory modules (SIMMs, DIMMs, or RIMMs)
• Adding more memory can sometimes greatly improve
  performance