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Chapter 6
Managing Memory
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
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
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
ROM on the Motherboard
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)
DRAM Storage
SRAM Storage
SRAM and DRAM
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
How SRAM Is Used in Different
Memory Caches
How Memory Caching Works
Different Types of SRAM
 Synchronous SRAM
 Burst SRAM
 Pipelined burst SRAM
 Asynchronous SRAM
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
Examples of Memory Modules
Summary of DRAM Technologies
continued…
Summary of DRAM Technologies
SIMM Technologies
 Rated by speed, measured in nanoseconds (ns)
 Can use either EDO or FPM technology
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)
DIMM Technologies
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
RIMM Technologies
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
Parity
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
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 costeffective?
 Match memory modules to the motherboard
How Much Memory Can Fit on the
Motherboard?
Example of an RDRAM Memory
Configuration
Installing Memory
 Protect chips against static electricity
 Use a ground bracelet
 Turn off power and remove cover to case
 Handle memory modules with care
Installing a SIMM Module
Installing a DIMM Module
Installing a DIMM Module
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?
How DOS Addresses Physical Memory
 Assigning addresses to both RAM and ROM:
• Occurs during booting (sometimes called memory
•
mapping)
Is done by every OS
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)
Areas of the Memory Map
Memory Map of Upper Memory
DOS Utilities That Manage Memory
 Himem.sys
• Device driver for all memory above 640K
• Allows DOS to access memory addresses above
1 MB
 Emm386.exe
• Contains software that loads device drivers and
other programs into upper memory
Using Himem.sys
Using Emm386.exe
Creating and Using Upper Memory
Blocks
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