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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 troub

leshoot memory How DOS and Windows 9x view and manage

memory

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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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Summary ofDRAM Technologies

continued

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Summary ofDRAM 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 theyhold

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 haseither 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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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 newSIMMs, DIMMs, or RIMMs, or if memoryerror messages occur?

What if the system locks up or you regularlyreceive error messages about illegal operations,and General Protection Faults occur duringnormal 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 memorymapping)

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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UsingHimem.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 onmemory modules (SIMMs, DIMMs, or RIMMs)

Adding more memory can sometimes greatly

improve performance