chpt4 understanding and managing memory

8/9/2019 Chpt4 Understanding and Managing Memory

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Chapter 4Chapter 4Understanding and Managing Memory


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Physical MemoryPhysical Memory

What are the 2 main CategoriesMemory used in the PC?

ROM, RAM

What is ROM (read-only memory)?

Data are pre-recorded in them and

cannot be removed and can only be read.Mainly used to store contains programs(firmware) to handle the devices. Thecontents are not lost even when thecomputer is turned off (nonvolatile).

What is RAM (Random AccessMemory)?

Type of computer memory that can beaccessed randomly. They are volatile,meaning that they lose their contentswhen the power is turned off. RAM isnormally refer to as the main memory,

the memory available to programs.


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Static and Dynamic RAMStatic and Dynamic RAM

What are the type of RAM available?DRAM (Dynamic RAM)

Static RAM (SRAM)

What is Dynamic RAM?

Commonly used as memory for

computers. It inexpensive and slow. Itneeds to be refreshed every fewmilliseconds to maintain its data. Theyare volatile, meaning that they losetheir contents when the power isturned off.

What isS

tatic RAM?It can hold data longer that DynamicRAM when the computer loss its power.

Does not need to be refreshed, whichmakes it faster; but it is also moreexpensive than dynamic RAM. Mainlyused as Cache memory.


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Role of System Memory in the PCRole of System Memory in the PC

How does it affectsPerformance?Insufficient memory can cause a

processor to work at 50% or even morebelow its performance potential.

How does it provide Software Support?

Newer programs require more memorythan old ones. More memory will giveyou access to programs that you cannotuse with a lesser amount.

How it contribute toPC Reliability andStability?

Bad memory is a major cause ofmysterious system problems. Usinghigh-quality memory will result in a PCthat runs smoothly and exhibits fewerproblems. Also, even high-quality

memory will not work well if you use thewrong kind.

How it affect future RAM Upgrade?There are many different types ofmemory available, and some are moreuniversal than others. Making a wisechoice can allow you to migrate yourmemory to a future system or continueto use it after you upgrade yourmotherboard.


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Common Main Memory Module

What are the common RAM modules?SIMM, DIMM, RIMM

What is SIMM?SIMM (single inline memory module).Implemented in: FPM (fast pagememory), EDO (extended data out)

memory. Speed is around 50ns, 60ns,70ns.

What DIMM?DIMM (dual inline memory module).Impemented in SDRAM (synchronousDRAM) and SDRAM II (DDR SDRAM).

SDRAM runs at 66Mhz, 100Mhz,133Mhz, which the Bus speed. SDRAMII run twice the Bus speed internally, ieif bus speed is 133Mhz then theinternal speed is 266Mhz.

What is RIMM?Rambus Inline Memory Module. Has thecapability to transfer up to 1.6 billionbytes per second. Runs at 400Mhz to800Mhz. Has 184pins.

72-pins SIMM

168-pins SDRAM

RDRAM


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ECC RAM, Parity and NonECC RAM, Parity and Non--parityparity

What is ECC (Error Checking andCorrection) RAM?

A type of memory that includes specialcircuitry for testing the accuracy ofdata as it passes in and out of memory.

What is required to Support ECC RAM?

To use ECC RAM, the Mainboard mustsupports ECC (check CMOS)

What isP

arity Check?A simple implementation of errorchecking.

How it Works?Parity check is either odd or even. Aparity bit (1 or 0)is added to every data

unit that are transmitted. The paritybit for each unit is set so that all byteshave either an odd number or an evennumber of set bits.If Even parity is used, then the paritybit for the binary number 10110101 willbe 1, the data sent will be 101101011.

Can Parity correct Error?No. It detect error only.

Can it detects Dual bits error?No. It cannot detect dual bits error.


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Logical Memory StructureLogical Memory Structure

How is the System Memory beenOrganized Logically?Conventional Memory, Upper MemoryBlock, High Memory Area, Extendedmemory

What is Conventional Memory or Base

Memory?The first 640 KB of system memory.Use by standard DOS programs,drivers, memory-resident programs, andanything that runs under standard DOS.

What is Upper Memory?

The 384 KB immediately aboveconventional memory. It is reserved foruse by system devices and for specialuses such as ROM shadowing anddrivers.

What is High Memory Area?This is the first 64 KB of extendedmemory. It is the only area in theExtended memory accessible by realmode program.

What is Extended Memory?

All the memory above the high memoryarea until the end of system memory.Used for programs and data when usingan operating system running inprotected mode, eg any version ofWindows. (Technically, the high memory

area is part of extended memory).


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Memory MapMemory Map

16-bits Programs

(DOS and Windows)

Device drivers and TSRs

(Terminate & Stay Resident)

DOS

640KB

1024KB

1088KB

0KB

Base or

Conventional

Memory (640KB)

Upper Memory

(384KB)

High memory area

(the first 64K of

Extended memory)

Extended Memory

(includes HMA)


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ExerciseExercise Check PC Memory MapCheck PC Memory Map

1. Get to the Command Prompta) Type the command:

mem /c/pb) Check the amount of Convention,

Upper Memory and Extendedmemory available

c) Find out which drivers are loaded in

Conventional and Upper Memory

2. Reboot the PC with StartUp Diska) Type the command:

mem /c/pb) Check the amount of Convention,

Upper Memory and Extended

memory availablec) Find out which drivers are loaded in

Conventional and Upper Memoryd) Compare with the Results in (1)


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Managing Memory in DOSManaging Memory in DOS

Why does Memory need to be managedin DOS?

DOS programs work only in theConventional memory of 640K. Withdrivers, OS files, etc, loaded, programmay not have enough memory left torun. There is a need to maximum

available conventional memory.

How can it be done?

Loading drivers, OS files out ofConventional memory to the UpperMemory and High Memory Area.

What need to be done?Configure the Config.sys:

1. Activate the Extended Memory

Driver used is HIMEM.SYS

2. Activate the Upper Memory

Driver used is EMM386.EXE

3. Move device drivers and TSR to theUpper Memory or HMA

Using devicehigh


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Using Config.sys to Activate Memory Drivers

What is Config.sys used for?Use to activate device drivers

Which environment uses Config.sys?

For DOS environment only. Windows donot need the Config.sys

When does Config.sys activated?Every time the PC is activated

device = c:\dos\himem.sys

device = c:\dos\emm386.exe noems

DOS=high,umb

devicehigh = c:\mouse

no ems do not

create expandedmemory

High - Load DOS in High Memory Area

UMB - accessible to Upper MemoryLoading device high - Load

mouse driverto HighMemory Area

Contents ofCONFIG.SYS


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Expanded MemoryExpanded Memory

What is Expanded Memory (EMS

)?A technique to use more than 1MB(megabyte) of main memory in DOS -based computers.

Is it still use in PC?

No. Windows 3.0 and all later versionsof Windows use Extended MemoryManager. Programs can use extendedmemory without interfering with oneanother.

Can Expanded memory be simulate withWindows?

Yes, Windows can simulate expandedmemory by using the EMM368.EXEdriver. The driver must be loaded inConfig.sys.


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Windows Virtual Memory

What is Virtual Memory?An imaginary memory area supported bysome operating systems. Windows 9ximplemented VM by using the Hard Diskspace to act as Memory

What is the purpose?Allows for the larger applications andmultitasking features of Windowsrequiring more RAM than physically.

How is VM being used?

For example, virtual memory mightcontain twice as many addresses as mainmemory. A program using all of virtualmemory, therefore, would not be ableto fit in main memory all at once.Nevertheless, the computer couldexecute such a program by copying into

main memory those portions of theprogram needed at any given pointduring execution.


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Managing Virtual Memory in WindowsManaging Virtual Memory in Windows

Can the Virtual Memory be Disable?No Recommended. Without VirtualMemory, PC performance drops.

Where is the Physical Virtual Memorylocated?

VM is also known as Swap File. It islocated in Located inC:\Windows\win386.swp

Where can you Manage Virtual Memory?

1. Control Panel

2. System applet

3. Performance tab

4. Virtual Memory

How can the VM be optimized?

By setting both the Maximum andMinimum to the same value. Therecommended value is about 2 times thephysical system memory.


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Memory BankMemory Bank

What is Memory Bank?A memory bank is the smallest amountof memory your system's processor canhandle at one time.

What is it role?

It determine if you require upgrades inpairs or not.

How it works?

Each bank contains a number of slots.Memory must be installed in "banks" inorder to be recognized by the system.

You must fill an entire memory bankeach time you install new memory, and amemory bank may consist of one, two orfour memory sockets.

Rough Guideline?16-bit system (286 or 386/SX)

2-30-pin SIMM sockets equalone bank

32-bit system (later 386 or 486)

4-30-pin SIMM sockets equalone bank; 1-72-pin SIMM socketequals one bank

64-bit system (Pentium, PentiumMMX, Pentium Pro or Pentium II)

two 72-pin SIMM sockets equalone bank, and one 168-pin DIMMsocket equals one bank.


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Memory Per BankMemory Per Bank

32-bit

Memory

Bus

8-bitSIMM

8-bitSIMM

8-bitSIMM

8-bitSIMM

Requires 4 x SIMM in 1 bank

(4 x 8 bits = 32 bits)

486 PCs Pentium PCs

32-bits

SIMM 1

32-bits

SIMM 2

Bank 0

32-bits

SIMM 3

32-bits

SIMM 4

Bank 1

Requires 2 x 32-bits SIMM per bank

(2 x 32 bits = 64 bits)


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Memory Per BankMemory Per Bank

Pentium PCs

64-bits

DIMM 1

64-bits

DIMM 3

64-bits

DIMM 2

Requires 1 x 64-bits DIMM per bank

(1 x 64 bits = 64 bits)

Bank 0 Bank 1 Bank 2

chpt4 understanding and managing memory

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