Understanding Memory

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Understanding Memory

• A Essentials Boot Camp
• Ivan Hurt
• Computer Tech Instructor

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What is memory?

• Where the computer temporarily stores electronic
  instructions and data

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Random Access Memory (RAM)

• Primary storage or main memory
• CPU and applications store information and
  instructions for future use
• Considered volatile memory
• Loses all its stored information when it is
  disconnected from its power source
• CPU uses unique locations of RAM, called memory
  addresses, to store information

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RAM Speed

• Measured in nanoseconds (ns, or billionths of a
  second)
• Older computers ranged from 80 ns to 120 ns.
• Today, it is common to find RAM access speeds of
  50 ns and faster
• You can determine the access speed of memory by
  looking at the last printed number on most DRAM
  chips for example, BAC4G302H-05 means the access
  speed is 50 ns.
• When installing new memory in a system is to
  match the speed of the memory to the speed of the
  motherboard's bus.

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RAM Size

• Bit -Binary digit equal to 0 or 1Byte
• Byte - 8 bits
• Kilobyte - 1024 bytes
• Megabyte - 1,048,576 bytes
• Gigabyte - 1,073,741,824 bytes
• Terabyte - 1,099,511,627,776 bytes

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Memory Concepts
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Read-Only Memory

• Often called ROM
• Installed on the motherboard and on some types of
  expansion boards
• ROM chips contain the system BIOS
• BIOS main function is to carry out boot
  operations by communicating with I/O devices and
  programs

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Static Random Access Memory

• Holds data as long as there is power available to
  the chip
• Power is provided by the system battery
• Through the use of its own internal clock, SRAM
  is synchronized with the motherboard's bus speed,
  thereby helping SRAM achieve higher speeds than
  DRAM.
• Level 2 is stored on SRAM chips
• Comes in sizes of 128 MB to 4 GB and is more
  expensive than DRAM.

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FPM, EDO, BEDO DRAM

• Fast Page Mode (FPM) DRAM
• Faster than DRAM but is relatively slow compared
  to other enhancements
• is not suitable for motherboard bus speeds
  greater than 60 MHz.
• Extended Data Output (EDO) DRAM
• Capability to hold several pieces of information
  at a time without having to be refreshed
• EDO was intended to run with Pentium systems
  rated between 60 MHz and 75 MHz
• Faster than FPM memory
• Burst EDO (BEDO) DRAM
• Process multiple (up to four) memory addresses at
  a time in small bursts

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DDR DDR2 SDRAM

• Double Data Rate SDRAM (DDR SDRAM)
• Sometimes referred to as SDRAM II
• Has a bus clock speed of 100 MHz and a transfer
  of data rate equal to 200 MHz
• Packaged on a 184-pin DIMM.
• DDR2 SDRAM
• transfers data at 2x the speed of standard DDR
• Comes in a 240-pin memory module
• Not backward compatible with DDR.

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MDDR RDRAM

• MDDR
• Also called Mobile DDR SDRAM
• Used in mobile devices
• Has a lower voltage of 1.8V, a lower power
  consumption.
• RDRAM (Rambus) DRAM
• Proprietary memory from Rambus, Inc.
• Improves on memory latency by transferring data
  in and out of memory at about 600 MHz
• Used a narrow bus width and comes on proprietary
  memory modules called RIMMs
• Used in conjunction with the newer Pentium 4s
  offered by Intel

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Video Memory

• Memory used on graphics cards
• Used for
• Higher resolution
• Faster video refresh rates
• 4 types of memory
• Video Random Access Memory (VRAM)
• Windows Random Access Memory (WRAM)
• Synchronous Graphics RAM (SGRAM)
• GDDR3 and GDDR4 (Graphics Double Data Rate 3 and
  Graphics Double Data Rate 4)

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4 types of video memory

• 4 types of video memory
• Video Random Access Memory (VRAM)
• Windows Random Access Memory (WRAM)
• Synchronous Graphics RAM (SGRAM)
• GDDR3 and GDDR4 (Graphics Double Data Rate 3 and
  Graphics Double Data Rate 4)

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4 types of memory cont

• Video Random Access Memory (VRAM)
• Bit depth is the number of bits assigned through
  VRAM to each pixel
• Specifically designed for video
• Acts as a buffer between the CPU and the monitor
• Windows Random Access Memory (WRAM)
• Does not mean Microsoft Windows memory
• Similar to VRAM
• More memory address storage space, resulting in
  better color depth and video resolution (1600 x
  1200)
• Faster than VRAM

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4 types of memory cont

• Synchronous Graphics RAM (SGRAM)
• Uses its own program instructions, called masked
  write and block write commands\
• Provide better throughput for graphic-intensive
  applications.
• Synchronized with the CPU clock speed and can
  support up to 100 MHz
• GDDR3 and GDDR4 (Graphics Double Data Rate 3 and
  Graphics Double Data Rate 4)
• Developed by ATI Technologies
• Target game consoles such as PlayStation and Xbox
  360

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Virtual Memory (Swap File)

• Operating systems are typically configured with a
  predetermined amount of hard drive space set
  aside to act as a memory buffer area for main
  memory (RAM).
• Data is temporarily moved, or swapped between
  memory and the hard drive
• Moving data out of main memory and placing it
  into a swap file frees up valuable space in main
  memory for other purposes.
• Swap file size can vary depending on the amount
  of free space available on the hard drive
• Manually configured. You can manually configure
  the swap file size or let the operating system
  take care of its configuration.

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Virtual Memory (Swap File) cont

• If you are running an application that uses up
  all of the current RAM, the extra memory needed
  to run the application can be provided
  automatically from virtual memory.
• Memory area is managed differently from main
  memory.
• Real memory addresses are data is stored in
  memory addresses within RAM
• With virtual memory, the operating system
  logically divides the set-aside hard drive space
  into memory pages that contain virtual memory
  addresses.
• Can typically hold more memory addresses than RAM
  can.
• Memory mapping is process by which these virtual
  memory addresses are converted into real memory
  is called memory mapping.

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Please remember

• If you get an operating system message stating
  that you are low on virtual memory, the best two
  options are to increase the operating system
  paging file or add more RAM.

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Memory quick reference
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Memory quick reference cont.

• 72-pin DIMM is used for FPM and EDO DRAM
• 72-pin SODIMM is used for FPM DRAM and EDO DRAM
• 44-pin SODIMM is used for SDR SDRAM
• 168-pin DIMM is used for SDR SDRAM
• 184-pin DIMM is used for DDR SDRAM
• 200-pin SO-DIMM is used for DDR SDRAM and DDR2
  SDRAM
• 240-pin DIMM is used for DDR2 SDRAM

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Parity

• 8 bits in 1 byte. Parity checking adds another
  bit, called a parity bit (ninth bit), to each
  byte of information that is stored in memory to
  verify its integrity.

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How parity works

• Computer checks to verify the even or odd state
  of the byte
• If it does not match its original assignment of
  even or odd parity, a memory parity error occurs,
  and the system may halt.
• Some parity errors may show up on the computer
  screen if the parity check fails.
• Parity error 1 indicates that the parity error or
  check has failed on the motherboard.
• Parity error 2 indicates that the error has most
  likely occurred on a memory expansion board.
• Parity is a tool used only to detect errors in
  memoryparity does not fix memory problems.

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Error Correction Code or Error Checking and
Correction

• ECC works in conjunction with the memory
  controller to not only detect errors found in
  data as it passes out of memory but also to fix
  single-bit errors with its built-in logic.
• ECC adds a special bit to data, called an error
  correction code bit, which is decoded by the
  memory controller for accuracy

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Logical memory divisions
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Memory map
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Know these terms

• EMM386.EXE uses Limulation (conversion of
  extended memory to expanded memory) to open
  access to the UMBs. This makes it possible to
  load programs and device drivers into memory
  using the AUTOEXEC.BAT and CONFIG.SYS files of
  DOS.
• Memmaker was introduced with DOS 6.0. This
  utility allows you to free up conventional memory
  by loading device drivers and terminate-and-stay-r
  esident programs (TSRs) into UMBs.
• Himem.sys is a memory device driver that also
  opens the HMA and directs programs to memory
  addresses in extended memory. Himem.sys must be
  loaded in the config.sys file for access to
  extended memory.

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Installing SIMMs, DIMMs, and RIMMs

• Unplug the power to the computer.
• Remove the system unit case cover.
• Make sure you are wearing an ESD wrist strap.
• Identify the SIMM or DIMM slots.
• With both hands, line up the SIMM, DIMM, or RIMM
  with the open motherboard memory slot.

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Installing SIMMs, DIMMs, and RIMMs cont.

• Push firmly on both sides of the SIMM, DIMM, or
  RIMM until it is seated in the slot. (SIMMs
  should be inserted into the motherboard at a 45
  angle.)
• Replace the system unit case.
• Take off your ESD wrist strap.
• Plug the power cord back into the computer, and
  turn the computer on.

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Other memory notes

• SIMMs should be installed in increments of two or
  four memory modules per memory bank.
• DIMMs can be installed in units of one (one
  module) per memory bank.
• RIMMs should be installed in pairs and be the
  same size, type, and speed. If you fail to match
  paired memory modules, your system may not boot,
  or you may receive a POST error.

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BIOS

• Newer computers
• During memory count , your memory will be
  automatically configured
• Older computers
• Make changes to your memory settings in the
  system BIOS configuration utility before the new
  memory is recognized

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How to get into the BIOS

• Dell, Acer, Compaq/HP
• Press F2 or Delete key
• Phoenix BIOS
• Ctrl Alt S
• Ctrl Alt Esc
• F1 or F2