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Memory. RAM is stored on internal microchips on-line ROM (Read only Memory) Stored permanently on chips in the computer Usually not altered or erased. Gives the computer its instructions when turned on

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Memory l.jpg
Memory

  • RAM is stored on internal microchips on-line

  • ROM (Read only Memory)

    • Stored permanently on chips in the computer

    • Usually not altered or erased.

    • Gives the computer its instructions when turned on

    • Contains the BIOS-Basic input/output System, amongst other things, which tells your computer how to operate and allows the software to take over.


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Computer Memory

  • Memory refers to data stored on microchips, storage refers to data stored permanently on disk, tap, CD - etc. A more definitive definition of Memory vs Storage

  • Early systems had 640K of RAM which was primarily reserved for DOS, this is sometimes termed base memory which is up to 1MB.

  • Current systems still reserve 640 K of RAM for DOS, as well as other functions such as keyboard buffer and video memory.

  • There are many different types of RAM that have evolved to serve various purposes. This link provides a RAM guide


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Computer Memory

  • Primary Storage (System Memory)

    • RAM (Random Access Memory) - on line

      • Short Term - lost when computer is turned off

      • Limited in amount available

      • Very fast, random access to information

  • Dynamic Ram (DRAM)

    • Cheaper type of Memory chip - pretty slow

    • Access time to chip measured in nanoseconds

      • Chip name -12=120 nano. -7=70 nano.

    • If CPU runs faster than memory you have problems

      • Takes at least two clock cycles to refresh memory

      • Wait states for DRAM


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CacheMemory Caching

  • Caching techniques avoid wait states.

  • A block of high speed RAM, typically Static RAM (SRAM) placed between the CPU and ordinary RAM

  • Cache Controller keeps likely needed data in Cache memory for high speed access.

  • Larger the cache memory, the more likely that the needed data will be available

  • Typical cache today is 64K - 128 K but can be higher

  • Primary cache or (L1) is in the CPU chip (typically 16K) Secondary Cache memory is external up until the P6.


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Mass Storage

  • Secondary Storage (Mass Storage)

    • Permanent storage and retrieval ability

    • Very large capacity

    • Not as fast as on line memory

  • Hard, Floppy, Zip disks, tape, CD-ROM Cartridge

    • Sequential and Random Access Media


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Hard Drives

  • Speed influenced by:

    • How fast the drive spins (7200-10,000 rpm)

    • Average Access (Seek) Time (5-8 milliseconds)

    • Data Transfer Rate-measured in MB/Sec.

      80+ Mb/Sec. Depending on the interface.

    • SCSI fastest and can be daisy chained

  • Storage Capacity

    • Used to be constrained to .5 GB by DOS 5/6 and BIOS

    • Interfaces such as ATA (.5 GB max), SCSI and IDE drives were not limited but had be partitioned.

    • Windows 95 allowed 2 GB, Windows 98 - no limit

    • More is better - typically 4 GB +


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Floppy Drives

  • Floppy Drives (3.5" and 5.25" Disk Drives)

    • 3.5" Disk Drive (High density = 1.44MB Medium = 720K)

    • 5.25" Disk Drive (High Density = 1.2MB Double = 540K)

  • Formatting Floppy Disks

    • Format a: formats disk to capacity of drive

    • Format a: /f:720 formats medium density

    • incorrect format will mess up your disk

  • Write protect

  • Disk Care

  • Floptical Disks up to 230Mb, Zip Disks 100MB +


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Input / Output Devices

  • Input devices

    • Keyboards 84 keys old std. 101 is current

    • Mouse (Serial Port)

    • Light Pens

    • Touch Screen

    • Voice

    • Joy Stick

    • Scanners

    • Video/Camera

    • Modem?


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Output Devices

  • Output Devices

  • Monitor (soft copy) CRT

    • MDA - Monochrome Display Adapter (2 colors)

    • CGA - Color Graphics Adapter -RGB- (16 colors)

    • EGA - Enhanced Graphics Adapter (64 colors)

    • VGA - Video Graphics Array (256 & up) & SVGA

  • Prior to VGA video signal was digital, almost all VGA is no analog

  • Pixels - Resolution (640X480 to 1280X1024)


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Output Devices continued

  • Standard is SVGA - 800 X 600, 1024x768

    • Influences on speed are memory, horizontal (kHz) and vertical scan rate (Hz)Refresh rate (Hz), interlacing,

    • VESA tries to establish video standards

    • 3D Video AcceleratorsAGP

  • Printers

    • Impact Printers - dot matrix (9 and 24 pin); daisy wheel

    • InkJet - better image resolution but slow

    • Thermal - specialized application

    • Thermal transfer (wax) - best color printers

    • Laser - 300 -1200 dpi


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Communication Ports

  • Serial Ports - Com Port, RS-232C

    • One lane wide - turns 8, 16, 32 wide path into 1

    • Speed measured in BPS 600 - 115,200 potential to go as high as 1 mill. in near future.

    • Usually used for modems and some printers

  • Parallel Ports

    • 8 lanes wide - Lpt ports

    • Most commonly used for printers but with bi-directional other connections are possible

    • Up to 100 times faster than serial



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Windows 98 Operating System

  • DOS - Where we came from

    • How to get around

    • Formatting disks

    • Copying files

    • Some basic commands

    • File and directory structure