Memory

Memory

Terms and Definitions

Chapter Objectives

After completing this chapter you will:

• Understand memory-related terminology.

• Be able to install and remove memory chips.

• Understand how memory works with different operating systems.

• Be able to optimize memory under different operating systems.

• Be able to troubleshoot memory problems.

Memory Overview

• Types of Memory:

– RAM (Random Access Memory) is volatile memory found on the

motherboard and stores the operating system, the software

applications, and the data being used by all of the software.

– ROM (Read Only Memory) is a non-volatile type of memory that

keeps data in chips even when the computer is shut off.

• Types of RAM:

– DRAM (Dynamic RAM) is less expensive, but slower than SRAM. It

requires periodic refreshing of the electrical charges holding the 1s

and 0s.

– SRAM (Static RAM) is faster but more expensive than DRAM. It is

also known as cache memory or L2 cache.

Memory Overview

• Memory Terms:

– Refreshing – Periodically rewriting information to the memory chip.

– Nanosecond – A billionth of a second.

– Pipelining – The process by which microprocessors and memory

obtain computer software instructions in a timely fashion.

– Cache Memory – also known as SRAM – can be found on the

motherboard, but normally is found inside the CPU. Cache memory

holds the most frequently used data so the CPU does not return to the

slower DRAM chips to obtain the data.

Memory Physical Packaging

• Types of Memory Packaging:

– DIP (Dual In-line Package) – A chip that has a row of legs running

down each side.

– SIMM (Single In-line Memory Module) – Available in 30-pin and 72-

pin configurations.

– DIMM (Dual In-line Memory Module) – 168-pin configuration and

used in Pentium, Pentium Pro, Pentium II or Pentium III

motherboards.

– DDR DIMM – 184-pin configuration and used in AMD Athlon

computers, Pentium 4 computers, and high-end servers.

– RIMM – Type of memory module used on video adapters and future

motherboards.

Memory Physical Packaging

• Methods of Error Checking:

– Parity – A method for checking the accuracy of data going in or out of

the memory chips.

– Non-parity – Memory chips that do not use any error checking.

– ECC (Error Correcting Code) – Uses a mathematical algorithm to

detect up to four-bit memory errors and correct one-bit memory

errors.

• A computer system that uses parity must have parity memory installed.

Memory Physical Packaging

Memory Chips

Memory – Figure #1

Memory Physical Packaging

184-Pin DDR DIMM and RIMM

Memory – Figure #2

Memory Chip Capacity

• Most Common Memory Capacity

• DIP chips

– 64Kb, 256Kb, or 1MB

• 30-Pin SIMM Modules

– 256Kb, 512Kb, 1MB, 2MB, and 4MB

• 72-Pin SIMM Modules

– 4MB, 8MB, 16MB, 32MB, 64MB, and 128MB

• DIMM Modules

– 8MB, 16MB, 32MB, 64MB, 128MB, 256MB, 512MB, and 1024MB

• RIMM Modules

– 64MB, 128MB, and 256MB

Identifying Chip Capacity and Speed

• The only way to be certain of the capacity is to install the SIMM in a

computer or research the manufacturer’s number on the internet.

• Access Time – How fast information goes into a memory chip or is

removed from the chip.

• The lower the number of nanoseconds, the faster the access time of the

memory chips.

Identifying Chip Capacity and Speed

Chip Capacity

Memory – Figure #3

Identifying Chip Capacity and Speed

Memory Chip Access Time

Memory – Figure #4

Memory Chip Technologies

• Technology to provide faster DRAM speeds:

– FPM (Fast Page Mode)

– EDO (Extended Data Out)

– BEDO (Burst EDO)

Memory Chip Technologies

• SDRAM (Synchronous DRAM) provides very fast burst memory access by placing new

memory address on the address bus before prior memory address retrieval and execution

completes.

– The PC100 SDRAM DIMMs are designed for the 100MHz front side bus.

– The PC133 SDRAM DIMMs are designed for the 133MHz front side bus, but will work

with the 100MHz motherboards.

– SPD (Serial Presence Detect) is an extra EEPROM feature of SDRAM DIMM PC100

and PC133 standard that adjusts the motherboard timings for the best CPU and RAM

performance.

– Registered SDRAM or Buffered SDRAM delays all data transfers by one clock to

ensure accuracy. It is used in network servers and higher end computers.

– Unbuffered SDRAM is the memory type most often used in home computers and in

low-to-medium powered computers.

• VCM (Virtual Memory Channel) is a memory chip alternative to SDRAM that fits in DIMM

slots. The motherboard chipset must support it.

Memory Chip Technologies

• Other Types of RAM:

– RDRAM (Rambus DRAM) – Developed by Rambus, Inc. and used in

Pentium 4 computers and some video adapters. RDRAM is packaged in

RIMMs.

• When RIMMs are used, all memory slots must be filled. Put an C-RIMM

(Continuity RIMM), which is a blank RIMM, in any empty slot.

– DDR RAM (Double Data Rate RAM) – also called DDR SDRAM – Data can

be transmitted on both sides of the clock signal (rising and falling edges).

– VRAM (Video RAM) – A type of memory found on a video card.

– WRAM (Windows RAM) – Dual-ported memory found on video adapters.

– SGRAM (Synchronous Graphic Random Access Memory) – Used on

video adapters and graphics accelerators and have special memory

techniques that speed up graphics-intensive functions.

Memory Chip Technologies

Memory – Table #2

Memory Banks

• Bank or Memory Bank is one or more memory chips that work together

to transfer data to and from the CPU and a device.

• External Data Lines or External Data Path is the electronic lines that

allow the microprocessor to communicate with external devices.

• Parity Chip is a memory chip on a memory bank that checks for data

accuracy.

Memory Banks

8088 Memory Banks

Memory – Figure #6

Memory Banks

80386 Memory Banks

Memory – Figure #7

Buying the Right 72-Pin SIMM

• Purchasing the correct memory can be difficult. Advertisements for

memory can often be confusing and even misleading. Always refer to

your motherboard documentation for the correct type of memory to install

with your computer.

Buying the Right 72-Pin SIMM

Sample of 72-Pin SIMM Advertisements

Memory – Figure #8

Populating Pentium and Higher Motherboards

• Computers with a Pentium processor and SIMM sockets have two

SIMMs that must be installed in one bank for the computer to operate.

• Pentium Pro computers usually have one DIMM socket as a bank and

two 72-Pin SIMM sockets for another bank of memory.

• Pentium 4s ship with DIMM or RIMM sockets.

Populating Pentium and Higher Motherboards

Pentium Memory Banks

Memory – Figure #9

Populating Pentium and Higher Motherboards

Pentium

Memory – Figure #10

Buying the Right DIMM or RIMM

• Be careful with purchasing DIMMs and always refer to the

documentation.

• DIMM Terminology:

– CAS (Column Address Strobe) Latency is the amount of time that

passes before the processor moves on to the next memory address.

– RAS (Row Address Strobe) is a signal that selects a specific

memory row.

Buying the Right DIMM or RIMM

Sample 168-Pin DIMM Advertisements

Memory – Figure #11

Buying the Right DIMM or RIMM

Sample DDR RAM DIMM and RIMM Advertisements

Memory – Figure #12

Memory Installation Rules

• When you start a bank, fill a bank.

• Use memory chips of the same capacity in a memory bank.

• All the chips in a bank should have the same access speed, if possible.

• All the chips in a bank should be of the same type, if possible.

• Some manufacturers require that higher capacity chips be placed in the

first bank.

• Always refer to the motherboard documentation for memory installation

requirements.

Same Capacity Chips in Bank

• Memory chips in a bank must work together. Each chip in the bank must

hold the same number of bits as the other chips.

– Two SIMM sockets require two equal capacity SIMMs to be installed.

– Always refer to the motherboard documentation for installation

requirements.

Laptop Memory

• Types of Laptop Memory:

– SO-DIMM (Small Outline-DIMM) – Special, smaller DIMM used in

laptop computers.

– SO-RIMM (Small Outline-RIMM) – Special, smaller RIMM used in

laptop computers.

Flash Memory

• Flash Memory is a type of non-volatile memory that holds data even when the

computer power is off.

– It is used with laptops because it is small, fast, and consumes little power.

– PCs use flash memory as a replacement for the BIOS chip.

• CompactFlash (CF) – is a small 50-pin removable storage device that allows

speeds up to 16 MBps CF has two main standards, CompactFlash and CF+

• SmartMedia – A trademark of the Toshiba Corporation and is used in a variety of

devices such as cameras, PDAs, musical instruments, printers, faxes, MP3

players, and scanners. There are two versions of SmartMedia cards – 3.3V and

5V.

• USB flash drives – also called a memory stick – allows storage up to 1 GB with

higher capacities expected.

Installing Memory Chips

• Installation Steps:

– Determine which chip capacities can be used for the system.

– Determine how much memory is needed.

– Determine what capacity chips go in each bank.

• Before removing or installing memory chips, always refer to the

documentation for you computer.

• Use an anti-static wrist strap when removing or installing memory chips.

Removing a DIMM/RIMM

• To remove a DIMM or a RIMM, push down on the outside edges of the

DIMM’s retaining tabs. The DIMM/RIMM lifts slightly out of the socket.

Removing a DIMM/RIMM

DIMM/RIMM Removal

Memory – Figure #17

Installing a DIMM/RIMM

• To install a DIMM or RIMM, align the notches on the DIMM/RIMM with the socket

and press down until the tabs close on the memory module.

• The following concepts summarize the most important memory installation steps:

– Always refer to the motherboard or computer documentation before

purchasing or installing memory.

– Install SIMMs into Pentium or higher computers in groups of two.

– When installing DIMMs, install one DIMM per bank.

– When installing RIMMs, install one RIMM per bank and fill the empty banks

with C-RIMMs.

– When installing PC100 and PC133 SDRAM DIMMs, install one DIMM per

bank.

– When installing DDR SDRAM DIMMs, insert one DIMM per bank.

Installing a DIMM/RIMM

DIMM/RIMM Installation

Memory – Figure #21

Configuring the Computer

• After memory has been installed in a computer, changes to the CMOS

Setup are required to recognize the new memory.

• The memory count during POST should equal the amount of memory

installed.

How Much Memory?

• The amount of memory that can be installed on the motherboard depends on two

things: the motherboard manufacturer and the microprocessor.

• Memory Modes:

– Protected Mode allows applications to access memory above 1 MB.

Applications must be specifically written for protected mode in order to use it.

– Real Mode – Early computers that could not access memory above 1 MB.

Most DOS applications were written for real mode microprocessors.

• Memory Map is a graphical representation of the amount of a microprocessor’s

memory addresses.

• UMA (Upper Memory Area) or Reserved Memory Area is an area of the

memory map between 640K and 1 MB that was traditionally reserved for ROM

chips. Unused portions of UMA can be made into upper memory blocks.

How Much Memory?

Intel Microprocessor Address Lines

Memory – Table #3

How Much Memory?

8088 Memory Map

Memory – Figure #22

How Much Memory?

Memory Map for 80386 through Pentium

Memory – Figure #23

Memory and Software Considerations

• Whether or not an application can use all of the RAM in the computer

depends on the operating system installed on the computer and the

operating system that the application was written for.

– An application specifically written for the DOS/Windows environment

running on a system with Windows 9x, NT, 2000, or XP behaves as if

it was installed on a system with DOS.

– An application specifically written for Windows NT/2000/XP will not

work in a Windows 9x or DOS/Windows 3x environment.

DOS/Windows 3.X and Memory

8088 Memory Map

Memory – Figure #24

Conventional Memory

• Conventional Memory is the area from 0 to 640K. DOS and all DOS

applications written for the 8088 computers ran in conventional memory.

• Upper Memory Area or Reserved Memory is the area of the memory

map between 640K and 1MB that was traditionally reserved for ROM

chips.

• EMS (Expanded Memory Specification) or Expanded Memory or LIM

(Lotus, Intel, Microsoft) Memory is a 64KB space in the memory map

normally reserved for ROM chips that allows paging up to 32MB of

memory, 64KB at a time.

Expanded Memory

Expanded Memory

Memory – Figure #25

Extended Memory

• XMS (Extended Memory Specification) or Extended Memory is the

area of the microprocessor’s memory map above 1 MB.

• For a system to use Extended Memory, the driver HIMEM.SYS must be

installed in the CONFIG.SYS file or automatically by the Windows

operating system.

Extended Memory

80386, 80486, and Pentium Memory Map

Memory – Figure #26

Adding More Cache/RAM

• Adding more RAM can make a noticeable difference in the performance

of a computer. For today’s computer, it is recommended to have at least

128MB of RAM.

• Disk Cache is a portion of RAM set aside for hard drive data that speeds

up hard drive operations.

• Windows 9x, NT, 2000, and XP have an integrated caching program for

CD and DVDs.

Windows 9X/NT/2000/XP Disk Caching

• Windows 98, NT, and 2000 have efficient memory management through

the VMM (Virtual Memory Manager).

– Virtual Memory is a method of using the hard disk space as RAM.

– Swap File is a block of hard drive space used like RAM by

applications.

– Pages – 4KB blocks of memory that the memory space is divided into.

Windows 9X/NT/2000/XP Disk Caching

Windows 98/NT/2000/XP Virtual Memory Usage

Memory – Figure #27

Monitoring Memory Usage Under Windows

• Each of these Windows utilities evaluate different performance areas: the

file system, the IPX/SPX compatible protocol, the kernel, the memory

manager, and Microsoft Network Monitor Performance Data.

– System Monitor is used with Windows 9x

– Performance Monitor is used with Windows NT

– Performance Utility is used with Windows 2000

• Thread is a unit of programming code that receives a slice of time from

Windows so it can run concurrently with other units of code.

Using a RAM Drive

• A RAM Drive is a virtual hard disk drive created from RAM. It is the

opposite of virtual memory.

• Most DOS applications run fine under Windows 9x, but those with

problems can be run in the Windows 9x’s MS-DOS mode.

• DOS applications run in an NT/2000/XP process called NTVDM (NT

Virtual DOS Machine). The NTVDM process simulates a 486 computer

running DOS.

Troubleshooting Memory Problems

• The following tips help with memory management:

– Add more RAM to help with performance

– Adjust virtual memory size

– Turn off the screen saver

– Remove the desktop wallpaper scheme or use a very plain one

– Put the swap file on the fastest hard drive

– Do not put the swap file on multiple partitions that reside on the same hard drive

– Put the swap file on a hard disk partition that does not contain the operating system

– Adjust your Temporary Internet Files setting

– Defragment the hard drive

– Remove unnecessary files and applications from the hard drive

– Empty the Recycle Bin