Managing Memory

1
Chapter 6

• Managing Memory

2
You Will Learn

• About the different kinds of physical memory and
  how they work
• How to upgrade and troubleshoot memory
• About Windows memory management

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RAM on the Motherboard

• Loses all data when PC is turned off (except data
  stored on CMOS chip)
• Two categories
• Static RAM (SRAM)
• Fast
• Used as a memory cache
• Dynamic RAM (DRAM)
• Slower requires constant refreshing

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DRAM
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SRAM
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COAST
COAST, an acronym for Cache On A STick, is a
packaging standard for modules containing SRAM
used as an L2 cache in a computer. COAST modules
look like somewhat oversided SIMM modules.
COAST modules were somewhat popular in the early
1990s, but as of 2004, most cache is build-in to
either the CPU or the motherboard. COAST modules
decoupled the motherboard from its cache,
allowing varying configurations to be created.
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Memory Technologies
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How SRAM Is Used in Different Memory Caches
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How Memory Caching Works
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Dynamic RAM Technologies

• Stored on DIMM, RIMM, or SIMM modules (plug
  directly into motherboard)
• Differences among these modules
• Width of data path that each type accommodates
• The way data moves from system bus to module

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Examples of Memory Modules
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DRAM Technologies
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DRAM Technologies (continued)
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DRAM

• SIMM technologies
• Can use either EDO or FPM technology
• DIMM technologies
• Can use either BEDO (burst EDO) or synchronous
  RAM (SDRAM)
• RIMM technologies
• Each socket must be filled to maintain continuity

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Identifying the DIMM Module
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RIMM Technologies
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Error Checking and Parity

• Parity
• Error-checking procedure in which every byte has
  an even number of ones or an odd number of ones
• Older method of testing integrity of bits
• Stored in RAM or secondary medium
• Sent over a communications device
• Error-correcting code (ECC)
• Current method of error checking that can detect
  and correct an error in a single bit

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Parity
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Other Memory Features

• CAS (column access strobe) latency
• RAS (row access strobe) latency
• Both CAS and RAS refer to the number of clock
  cycles it takes to write or read a column or row
  of data

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Memory Speeds Factors to Consider

• Speed of memory in ns, MHz, or PC rating
• How much memory is installed
• Memory technology used
• CL (CAS Latency) rating
• ECC/parity or non-ECC/nonparity

CL- the number of clock cycles between the time a
read command is sent and the data is available
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Factors That Contribute to Memory Speed
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PC RATINGS
It is the rating standard that involves
Data-transfer speed on the Memory BUS between the
CPU and Memory when running any application. The
rating refers directly to the maximum bandwidth
obtainable and indirectly to the memory clock
rate. PC2100, for example, has a 2.1GB/S
maximum transfer rate, and a clock rate of
133MHz. PC4000, as another example, has a 4GB/S
ideal transfer rate and a 250MHz clock. To obtain
the clock rate from the PCXXXX rating, divide the
rating by 16. Multiply the MHz rating by 16 to
obtain the bandwidth rating.
The DDRXXX is just two times the actual clock
speed i.e. DDR400 is clocked at 200MHz. if you
want know the PC-XXXX speed of the DDRXXX speed,
times it by 8
DDR-IPC1600 DDR 200MHz Data-rate (100 Clk x 2)
1.6Gb/SecPC2100 DDR 266MHz Data-rate (133 Clk
x 2) 2.1Gb/SecPC2400 DDR 300MHz Date-rate (150
Clk x 2) 2.4Gb/SecPC2700 DDR 333MHz Data-rate
(166 Clk x 2) 2.7Gb/SecPC3000 DDR 366MHz
Data-rate (183 Clk x 2) 3.0Gb/SecPC3200 DDR
400MHz Data-rate (200 Clk x 2) 3.2Gb/Sec
DDR-IIPC4300 DDR 533MHz Data-rate (266 Clk x
2) 4.3Gb/Sec
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Upgrading Memory

• What to look for when buying memory chips and
  modules
• How much and what kind of memory to buy
• Reading ads about memory modules
• Installing memory

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What to Look for When Buying Memory Chips and
Modules

• Use type, size, density, and fastest speed
  supported by the motherboard
• Match tin leads to tin connectors and gold leads
  to gold connectors
• Beware of remanufactured and re-marked memory
  chips

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How Much and What Kind of Memory to Buy

• Determine how much memory you have and need
• Identify the number, type, and size of memory
  modules supported by your motherboard
• Determine how much memory can you afford
• Match memory modules to the motherboard

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Using Motherboard Documentation to Select Memory
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Using Motherboard Documentation to Select Memory
(continued)
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RDRAM Memory Configuration
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Installing Memory

• Protect chips against static electricity
• Usually modules pop into place easily and are
  secured by spring catches on both ends

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Installing a SIMM Module
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Installing a DIMM Module
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Installing a DIMM Module (continued)
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Installing a RIMM Module
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Troubleshooting Memory

• What to do if the computer does not recognize new
  SIMMs, DIMMs, or RIMMs, or memory error messages
  appear
• Recurring errors during normal operations can
  mean unreliable memory

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Windows Memory Management

• Evolution of OS memory management
• Windows 9x memory management
• Windows NT/2000/XP memory management

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Evolution of OS Memory Management

• DOS and Windows 9x
• Complicated must deal with conventional, upper,
  and extended memory for backward compatibility
• Windows NT/2000/XP
• Eliminates complexity memory is simply memory
  all memory addresses are used the same way
• Causes loss of backward compatibility

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Division of Memory Under DOS and Windows 9x
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Assignment of Windows 9x Memory Addresses
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How Memory Addresses Are Used
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How Memory Addresses Are Used (continued)
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Memory Management Evolution
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Windows 9x Memory Management

• Views and manages memory addresses as DOS did
• Runs in protected mode and uses virtual memory
  does a better job managing extended memory than
  DOS

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How Windows 9x and DOS Manage Memory Addressing
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Windows 9x and DOS Utilities That Manage Memory

• Himem.sys
• Device driver for all memory above 640K
• 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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How Windows 9x Manages Virtual Memory

• Automates virtual memory management
• Stores virtual memory in swap file and manages
  that memory for application programs
• Controlled by the VMM (memory paging)
• Symptoms of excessive memory paging
• Very high CPU use
• Very slow system response
• Constant hard drive use

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Windows NT/2000/XP Memory Management
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How Windows 2000/XP Manages Virtual Memory

• Default size of paging file is set to 1.5 times
  amount of RAM installed
• Guidelines for managing paging files
• Set initial and maximum size of file to same
  value
• Balance file size with disk space usage
• Move paging file to a volume other than boot
  volume
• Remember that memory dumps cannot be captured if
  the paging file is on a different physical disk
  from the OS

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Summary

• Memory
• Required in order for a system to work
• Stored on microchips, which are often stored on
  memory modules (SIMMs, DIMMS, RIMMs)
• Adding more memory can improve system performance
• How DOS, Windows 9x, and Windows NT/2000/XP
  manage memory