MotherboardA motherboard is the main printed circuit board in a computer that contains the central processing unit, appropriate coprocessor and support chips, device controllers, memory, and also expansion slots to give access to the computer’s internal bus. The motherboard is the PCs center of activity. All devices in a computer are in some way connected to the motherboard.

After CPU, motherboard is the second most important component in the system and therefore, it definitely needs special attention.

The design of a motherboard is dependent on the type of CPU and mainly oriented around the chipset present onboard.

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The motherboard features decide the system performance to a great extent, upgrade potential, etc.

As there are numerous types of processors, there are different types of motherboards as well.

The classification is usually done on the basis of types of CPU sockets carried by these boards.

Functions of Motherboard

Motherboard provides a substrate upon which other components of a system such as CPU, RAM, ROM, Chipset, and Expansion Slots can reside.

Motherboard provides the electrical connection between various components in the system.

Motherboard provides interface for various add-on cards such as 3D graphics cards, NIC, Sound cards, etc. through various expansion slots such as PCI, ISA, AGP, etc.

Motherboard provides the necessary interface with a host of I/O devices. E.g., on-board IDE or SCSI interface for hard-disks, CD-ROM drives etc.

They also provide other traditional I/O connectors such as PS/2interface, RS232 serial COM ports, Bi-directional parallel port (LPT), Joystick connection through game port, floppy disk interface, etc.

The battery driven RTC chip on the motherboard stores CMOS setup information.

They provide IR port, CNR slot, IEEE 1394, USB for attaching emerging high-speed serial devices.

Components of a Motherboard

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There are various components of a motherboard which fixed together into a single unit leads to the proper functioning of a motherboard.

(1) Chips: The active devices on the motherboard are gathered together in chips. These are tiny electronic circuits which are crammed with transistors.

(2)Socket: These are holders, which have been soldered to the motherboard. The sockets are built to exactly match a card or a chip.

(3) Plugs, Connectors, and Ports: The motherboard also contains a number of inputs and outputs, to which various equipment can be connected. Most ports (also called I/O ports) can be seen where they end in a connector at the back of the PC. These are:

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Ports for the keyboard and mouse. Serial ports, the parallel port, and USB ports.

Sockets for speakers/microphone etc.

Motherboard Form FactorsA motherboard form factor just describes the dimensions or size of the motherboard and what the layout of the motherboard components is. It is

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important to understand the different motherboard form factors, because you cannot take any motherboard and place it in a computer case. You must put an ATX board in an ATX case.

Since the beginning of PCs, the following types of motherboard Form Factors appeared in the market:

Active and Passive Backplane. Full size AT Mini or Baby AT LPX ATX Mini-ATX NLX

Active and Passive Backplane:

In Passive Backplane, PC‘s major Motherboard components such as processor, memory chips, support circuitry, etc. are not placed on a single board; rather they are placed on a expansion boards plugged into slots of another board.

Allow easy upgrade of entire system. Active Backplane contain all typical components found on a typical

motherboard except the Processor and the components which are directly attached to the processor such as cache memory, system clock, etc.

Backplane systems didn’t gain much popularity.

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Active and Passive Backplane

Full Size AT:

Released in 1984. 12 Inches Wide and 13.8 Inches in length. Can fit into full size tower or desktop. Provision for 8 expansion slots. No uniform standard followed in component layout. Some older AT motherboards do not contain any onboard I/O ports

and contained I/O ports in the form of Pin Headers.

Full Size AT

Baby AT:

• 8.66 inches wide and 13 inches long.

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• Compatible with almost every type of case.

• Mounting in newer Baby-AT boards.

• Problem full length expansion cards.

Baby AT

LPX:

• 8.66 inches wide and 13 inches long.

• Developed for Slimline or Low Profile cases used by some branded manufactures.

• Western Digital first introduced this form factor in some of their systems.

• Single Slot motherboards and Riser cards.

• Built in video and I/O connectors.

• Limited Upgradability and poor cooling.

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LPX

ATX:

Released by Intel in 1995. The latest Pentium 4 motherboards are based on ATX version 2.3. 9.6 inches wide and 12 inches long. Integrated I/O port connectors. Better clearance for expansion cards. Proper positioning of CPU and Memory. Dust and Dirt control. Smaller length of internal I/O connector cables. Lower manufacturing costs.

ATX

Mini-ATX:

11.2 inches in length and 8.2 inches wide.

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More cost-effective.

Can fit into both ATX and mini-ATX cabinets

Mini-ATX

NLX:

• Quickly replaceable motherboards.

• Larger size processors and memory modules.

• Backplane flexibility.

• Additional features such as built-in multimedia solutions, video playback, extended audio, etc.

Comparison of Common Form Factors

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Style Width

(Inches)

Length

(Inches)

Cases Power Supply

Where Found

Full AT 12 11-13 Full Tower / Desktop

AT Style PC-AT 286/386

Baby AT 8.66 10-13 ALL but Slimline AT Style PC-AT 286/386/486

ATX 12 9.6 ATX ATX Current PCs

Mini-ATX 11.2 8.2 ATX ATX Current PCs

LPX 9 11-13 AT AT Old Retail PCs

Mini-LPX 8-9 10-11 AT AT Old Retail PCs

NLX 8-9 10-13.6 ATX ATX New Retail PCs

ChipsetThe Chipset is the glue that connects the microprocessor to the rest of the motherboard and therefore to the rest of the computer. On a PC, it consists of

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two basic parts -- the Northbridge and the Southbridge. All of the various components of the computer communicate with the CPU through the chipset.

Chipset History

• At one time, multiple, smaller controller chips performed different types of functions.

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• There was a separate chip (often more than one) for each function: controlling the cache, performing direct memory access (DMA), handling interrupts, transferring data over the I/O bus, etc.

• Over time these chips were integrated to form a single set of chips, or chipset that implements the various control features on the motherboard.

What is Chipset?

• A chipset is just a set of chips

• Logic circuits that are the intelligence of the motherboard.

• Controlling data transfers between the processor, cache, system buses, and peripherals—basically everything inside the computer.

• A highly integrated circuit used to perform a set of functions.

• The term “chipset” is also used to refer to the main processing circuitry on many video cards.

Chipset Features and Functions

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Chipset processor support:

• A chipset is designed to work with certain set of processors.

• Most chipsets support one “class” or generation of processor.

• Processor speed support is also controlled by chipsets as faster processors require chipset control circuitry capable of handling them.

• Some chipsets are capable of supporting more than one processor.

Chipset Cache support:

• Chipset determines how much secondary cache (L2) is supported.

• Determines secondary cache type support like asynchronous, synchronous burst & pipeline burst.

• Secondary cache write policy – Write back or Write through.

• Controls the maximum amount of memory the system can cache.

Chipset Memory Support :

• The chipset dictates the maximum amount of RAM that you can have on the system.

• The chipset controls the type of RAM that can be used. It determines whether our motherboard can have EDO, SDRAM, DDR SDRAM or RDRAM etc.

• Error correction logic is provided as part of the memory control circuits of the chipset. A chipset supports either parity, ECC or both. Some of the desktop does not support any of the above logic.

Chipset Timing and Flow control:

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• One of the chipset’s most important functions is controlling memory reads and writes, and transfers to the local bus (usually PCI and/or AGP) by the processor.

• The chipset performs address decoding.

• Cache and memory data transfer to and from the processor.

• The chipset controls the flow information from the local bus (PCI) to memory as well as from PCI directly to processor.

• Responsible for managing memory system timing – reducing the processor wait state and inserting wait states wherever necessary to ensure that the processor is not going ahead of memory.

• Auto detection of memory.

Peripheral and I/O Bus control:

• The chipset controls the various types of buses (PCI, AGP, ISA etc.) and transfers information to and from them and the processor and memory.

• The chipset dictates what types of buses the system can support.

• The chipset has bus bridges to connect together the different bus types that it controls.

• The chipset integrates the IDE/ATA Hard disk controller. The data transfer rate of the IDE devices depends on the chipset.

• Direct Memory Access and Bus Mastering of PCI devices is provided by the chipset.

• The interrupt controller provides the means by which I/O devices request attention from the processor to deal with data transfers. This work is performed by Interrupt controllers which are integrated in the chipset.

• USB support (USB controller) is implemented as part of the chipset.

• Plug and Play – is a specification which enables device to have their system resource usage (IRQ, DMA) set automatically.

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Power Management support:

• Most recent chipsets support a group of features that work together to reduce the amount of power used by the PC during idle periods.

• There are a number of different protocols that works together to make power management work like Energy Star, APM, DPMS, SMM, ACPI etc.

ARCHITECTURE OF CHIPSET

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WORKING OF CHIPSET

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Expansion SlotsThe most visible parts of any motherboard are the expansion slots. These look like small plastic slots, usually from 3 to 11 inches long and approximately 1⁄2 inch wide. As their name suggests, these slots are used to install various devices in the computer to expand its capabilities. Some expansion devices that might be installed in these slots include video, network, sound, and disk interface cards.If you look at the motherboard in your computer, you will more than likely see one of the main types of expansion slots used in computers today:

ISA PCI PCIe AGP AMR CNR

Each type differs in appearance and function. In this section, we will cover how to visually identify the different expansion slots on the motherboard.

ISA Expansion Slots:

If you have a computer made before 1997, chances are the motherboard has a few Industry Standard Architecture (ISA) expansion slots. They’re easily recognizable because they are usually black and have two parts: one shorter and one longer. Computers made after 1997 generally include a few ISA slots for backward compatibility with old expansion cards (although most computers are phasing them out in favor of PCI).

ISA expansion slots

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PCI Expansion Slots:

Most computers made today contain primarily Peripheral Component Interconnect (PCI) slots. They are easily recognizable because they are short (around 3 inches long) and usually white. PCI slots can usually be found in any computer that has a Pentium-class processor or higher.

PCI Expansion Slots

PCIe Expansion Slots:

The newest expansion slot architecture that is being used by motherboards is PCI Express (PCIe). It was designed to be a replacement for AGP and PCI. It has the capability of being faster than AGP while maintaining the flexibility of PCI. And motherboards with PCIe will have regular PCI slots for backward compatibility with PCI.

PCIe Expansion Slots

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AGP Expansion Slots:

Accelerated Graphics Port (AGP) slots are very popular for video card use. In the past, if you wanted to use a high-speed, accelerated 3D graphics video card, you had to install the card into an existing PCI or ISA slot. AGP slots were designed to be a direct connection between the video circuitry and the PC’s memory. They are also easily recognizable because they are usually brown, are located right next to the PCI slots on the motherboard, and are shorter than the PCI slots.

AGP Expansion Slots

There are seven different speed levels for PCIe, and they are designated 1X, 2X, 4X, 8X, 12X, 16X, and 32X. These designations roughly correspond to similarly designated AGP speeds. The slots for PCIe are a bit harder to identify than other expansion slot types because the slot size corresponds to its speed. For example, the 1X slot is extremely short (less than an inch). The slots get longer in proportion to the speed; the longer the slot, the higher the speed.The reason for this stems from the PCIe concept of lanes, which are the multiplied units of communication between any two PCIe components and are directly related to physical wiring on the bus. Because all PCIe communications are made up of unidirectional coupling between devices, each PCIe card negotiates for the best mutually supported number of lanes with each communications partner.

AMR Expansion Slots:As is always the case, Intel and other manufacturers are constantly looking for ways to improve the production process. One lengthy process that would often slow down the production of motherboards with integrated analog I/O functions was FCC certification. The manufacturers developed a way of separating the analog circuitry, for example, modem and analog audio, onto its

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own card. This allowed the analog circuitry to be separately certified (it was its own expansion card), thus reducing time for FCC certification. This slot and riser card technology was known as the Audio Modem Riser, or AMR. AMR’s 46-pin slots were once fairly common on many Intel motherboards, but technologies including CNR and Advanced Communications Riser (ACR) are edging out AMR. In addition and despite FCC concerns, integrated components still appear to be enjoying the most success comparatively.

An AMR slot

CNR Expansion Slots:The Communications and Networking Riser (CNR) slots that can be found on some Intel motherboards are a replacement for Intel’s AMR slots. Essentially, these 60-pin slots allow a motherboard manufacturer to implement a motherboard chipset with certain integrated features. Then, if the built-in features of that chipset need to be enhanced (by adding Dolby Digital Surround to a standard sound chipset, for example), a CNR riser card could be added to enhance the onboard capabilities. Additional advantages of CNR over AMR include networking support, Plug and Play compatibility, support for hardware acceleration (as opposed to CPU control only), and no need to lose a competing PCI slot unless the CNR slot is in use.

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PROCESSOR A processor is the logic circuitry that responds to and processes the basic instructions that drive a computer. The term processor has generally replaced the term central processing unit (CPU). The processor in a personal computer or embedded in small devices is often called a microprocessor.

The “brain” of any computer is the central processing unit (CPU). This component does all the calculations and performs 90 percent of all the functions of a computer.

From the 2MHz Intel 4004 launched in 1971 to the mind boggling 2 GHz Pentium 4 in 2002 from the same company-the Microprocessor technology has come across a long way over these thirty years.

A microprocessor is an integrated circuit (IC) that contains a complete CPU on a single chip.

All the processors are backward compatible with 8086, and therefore appropriately called as x86 processors.

The original IBM PC design was based on CPUs incorporating CISC architecture while its nearest rival, the Apple Macs were designed on Motorola 680x0 and IBM PowerPC processors features featuring RISC architecture.

Though initially all x86 processors came with CISC architecture, present day x86 processor architecture is actually a perfect blending of RISC and CISC.

Working of CPU

The CPU is centrally located on the motherboard. Since the CPU carries out a large share of the work in the computer, data pass continually through it. The

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data come from the RAM and the units (keyboard, drives etc.). After processing, the data is send back to RAM and the units.

The CPU continually receives instructions to be executed. Each instruction is a data processing order. The work itself consists mostly of calculations and data transport:

Data have a path to the CPU. It is kind of a data expressway called the system bus.

CISC and RISC instructions

CISC (Complex Instruction Set Computer):

The first CPUs had a so called Complex Instruction Set Computer (CISC). This means that the computer can understand many and complex instructions. The X86 instruction set, with its varying length from 8 to 120 bit, was originally developed for the 8086 with its mere 29000 transistors.

RISC (Reduced Instruction Set Computer):

The RISC instructions are brief and the same length (for example 32 bit long, as in Pentium Pro), and they process much faster than CISC instructions. Therefore, RISC is used in all newer CPUs. However, the problem is that the instructions arrive at the CPU in 8086 format. Thus, they must be decoded for every new CPU generation; the instruction set has been expanded. The 386 came with 26 new instructions, the 486 with 6 new instructions, and Pentium with 8 new instructions. These changes mean that some programs require at least a 386 or a Pentium processor to work.

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Processor Generation and Families

Processor Generation Processor Families

First Generation (P1) i8086, i8088, NEC V-20

Second Generation (P2) i80286

Third Generation (P3) i80386SX, i80386DX

Fourth Generation (P4) i80486SX, i80486DX, i80486DX2, i80486DX4, AMD 486DX4, AMD/Cyrix 586

Fifth Generation (P5) Intel Pentium, Pentium Overdrive, AMD K6, Cyrix M-I/M-II

Sixth Generation (P6) Pentium Pro, Pentium II, Celeron, Pentium III, Pentium IV, AMD K6-2, AMD K6-3, VIA Cyrix III

Seventh Generation (P7) AMD Athlon, AMD Duron, AMD Opteron, AMD Turium, Intel ItaniumI/ItaniumII

Inside a Modern Processor

BIU Internal Registers L1 Cache Control Unit ALU Integer Execution Unit FPU Branch Prediction Unit Virtual Memory Support

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Processor Data Bus

There are data busses both inside and outside the processor. Usually by the term Data Bus we mean External Data Bus. Internal data bus width is largely determined by the widths of the

CPU Internal Registers. Each wire in the data bus carries one bit information.

Processor Address Bus

The Front Side Bus: FSB is also known as the Processor Bus, Memory Bus, or System Bus and connects the CPU with the main memory and is used to connect to other components within the computer.

The FSB can range from speeds of 66 MHz, 133 MHz, 100 MHz, 266 MHz, 400 MHz, and up.

The FSB speed can generally be set either using the system BIOS or with jumpers located on the computer motherboard.

The address bus part of a host processor bus (FSB) or memory bus physically consists of a set of wires that carry the addressing information used to select a memory or information used to select a memory or I/O port location to which the data is being retrieved by the CPU.

As with the data bus, each wire in the Address bus carries a single bit of address information.

Backside Bus

The back side bus is a special bus that allows communication between the CPU and the l2 cache, which is a device that offloads some specialized computing tasks to make the CPU operate more quickly. Nothing besides the cache and CPU are connected to the back side bus.

Processor Control Bus

The control bus represents the different control signals such as Memory and I/O Device Read, Memory Write, DMA Hold, Interrupt, etc.

Some Lines are output only, some lines are input only.

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Processor numbers are based on a variety of features that may include the processor's underlying architecture, cache front side bus, and clock speed

• Architecture: Basic design of a microprocessor. May include process technology and/or other architectural enhancements.

• Cache (MB/KB): A temporary storage area for frequently accessed or recently accessed data. Having certain data stored in a cache speeds up the operation of the computer. Cache size is measured in megabytes (MB) or kilobytes (KB).

• Front Side Bus: The connecting path between the processor and other key components such as the memory controller hub. FSB speed is measured in GHz or MHz

• Clock Speed: Speed of the processor's internal clock, which dictates how fast the processor can process data. Clock speed is usually measured in GHz (gigahertz, or billions of pulses per second).

Hyper Threading (HT)

Hyper Threading is a new technology in Intel P4 processor to increase the CPU performance to immense level.

Hyper Threading means

1 physical processor and 2 logical processor.

Normally More than one processor systems will give a high performance than single processor. But introducing multiple processors in a system involves high cost. HT is a solution which is cost-effective and High-Performance.

See the video of HYPER-THREADING to understand about this topic.

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Processor Sockets

Socket Number Pins Pin Layout Voltage Supported Processors

Socket 1 169 17x17 PGA 5v 486 SX/SX2, DX/DX2, DX4 Overdrive

Socket 2 238 19x19 PGA 5v 486 SX/SX2, DX/DX2, DX4 Overdrive, 486 Pentium Overdrive

Socket 3 237 19x19 PGA 5v/3.3v 486 SX/SX2, DX/DX2, DX4, 486 Pentium Overdrive, AMD 5x86

Socket 4 273 21x21 PGA 5v Pentium 60/66, Overdrive

Socket 5 320 37x37 SPGA 3.3/3.5v Pentium 75-133, Overdrive

Socket 6 235 19x19 PGA 3.3v 486 DX4, 486 Pentium Overdrive

Socket 7 321 37x37 SPGA VRM Pentium 75-233+, MMX, Overdrive, AMD K5/K6, Cyrix M1/II

Socket Number Pins Pin Layout Voltage Supported Processors

Socket 8 387 dual pattern SPGA

Auto VRM Pentium Pro

Socket 370 (PGA370)

370 37x37 SPGA Auto VRM Celeron/Pentium III PPGA/FC-PGA

Slot A 242 Slot Auto VRM AMD Athlon PGA

Socket A (Socket 462)

462 PGA Socket Auto VRM AMD Athlon/Duron SECC

Slot 1 (SC242) 242 Slot Auto VRM Pentium II/III, Celeron SECC

Slot 2 (SC330) 330 Slot Auto VRM Pentium II/III Xeon

Processor Packaging

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DIP PGA CPGA SPGA FC-PGA DIP MCM LCC PLCC PQFP BGA SEC

Standardized Sockets and Slots

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Originally the purpose of providing a CPU socket on the motherboard was just to provide a place to insert a processor onto the motherboard.

However over the last few years Intel and AMD, the two major processor makers in the PC world, have defined several socket interface standards for PC motherboards.

These are standardized Socket and Slot specifications to be used with matching processors that are specifically designed for them.

Inserting a CPU

There are several types of CPU sockets available. Today virtually all desktop PCs come with some variation of the SEC packaging. Other CPUs are generally not worth upgrading and may be one of two common types of package:

Low-insertion-force (LIF) Zero-insertion-force (ZIF)

ZIF Socket with CPU Inverted

Computer Memory

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The term computer memory refers to any form of electrical storage device inside a computer. However, most often the term refers to fast, temporary forms of storage. If the processor needs to retrieve each and every piece of data from the hard disk drive, the speed of the processor will become considerable slow. But when the same piece of data is stored in the computer memory, the processor can access it more quickly. Most forms of memory are intended to store data temporarily.

Types of Computer Memory

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Cache and registers RAM ROM FLASH Memory EMBEDED Memory OTPICAL Memory

Cache:

To cache is to set something aside, or to store for anticipated use.

Caching, in PC terms, is the holding of a recently or frequently used code or data in a special memory location for rapid retrieval.

Speed is everything when it comes to computers.

While working, the CPU is constantly requesting and using information and

Executing code. The closer the necessary data is to the CPU, the faster the system can locate it and execute the operation.

High-speed memory chip generally used for caching is called static RAM (SRAM).

L1 Cache:

Starting with the 486 chips, a cache has been included on every CPU. This original on-board cache is known as the L1 (level 1) or internal cache.

All commands for the processor go through the cache. The cache stores a backlog of commands so that if await state is encountered, the CPU can continue to process using commands from the cache.

Caching will store any code that has been read and keep it available for

The CPU to use. This eliminates the need to wait for fetching of the data from DRAM.

Registers

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These are memory cells built right into the CPU that contain specific data needed by the CPU, particularly the arithmetic and logic unit (ALU).

L2 Cache:

Additional cache can be added to most computers, depending on the motherboard. This cache is mounted directly on the motherboard, outside the CPU.

The external cache is also called L2 (level 2) and is the same as L1, but larger. L2 can also (on some motherboards) be added or expanded.

L3 Cache:

Tertiary (third) caches originated out of server technology, where high-end systems use more than a single processor.

Initially an L-3 cache memory chips were built directly into the North Bridge but now it comes built-in with the processor.

RAM

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The capacitor can retain charge for a fraction of a second, so DRAM requires an entire circuitry to keep the capacitors charged. The process of recharging the capacitors is known as refreshing.

. Each transaction between the CPU and memory is called a bus cycle Memory controller handles the movement of data to and from the

CPU and the system memory banks. The memory controller is also responsible for the integrity of the data as it is swapped in and out.

o Parityo ECC

Types of RAM

Static RAM (SRAM): Dynamic RAM (DRAM): FPM DRAM: EDO DRAM: SDRAM: DDR SDRAM: RDRAM: DDR2: VRAM:

SRAM:

SRAM memory requires no refresh at all, it will maintain its information so long as it has sufficient power to keep it. This is due to the fact that internally, the SRAM component is made up of flip-flop circuitry, which does not depend on refreshing.

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DRAM:

The Dynamic RAM like SDRAM too consists of transistors, but it has only a pair of transistor unlike four to six transistors in SRAM. Another difference is that, DRAM stores each bit of data in a separate capacitor within an integrated circuit. Now a capacitor leaks charge, because of which data is stored in a DRAM for on it a tiny fractions of seconds before getting lost. To overcome this problem, the DRAM needs to be refreshed periodically. Because of periodic refreshing it gets its name as “dynamic” and hence called Dynamic RAM (DRAM).

The DRAM is slower than SRAM, but the advantage is that it requires less power is also inexpensive.

FPM DRAM:

The Fast Page Mode DRAM (FPM DRAM) is slightly faster than conventional DRAM. This is because of the fact that FPM DRAM works by eliminating the need for a row address if data is located in the row previously accessed. It is sometimes called page mode memory.

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EDO DRAM:

Extended data-out DRAM (EDO RAM) is much faster version of DRAM. Unlike conventional DRAM which can only access one block of data at a time, EDO RAM usually start fetching the next block of memory as soon as it sends the previous block to the processor. It is about five percent faster than FPM. Maximum transfer rate to L2 cache is approximately 264Mbps.

SDRAM:

This type of memory synchronizes its input and output signals with the incoming clock that is used in the system board. By doing so, data transactions can continually take place with each successive rising edge of the clock. SDRAM is about five percent faster than EDO RAM and its transfer rate to L2 cache is approximately 528 Mbps.

DDR RAM:

Double Data Rate SDRAM also known as DDR RAM is just like SDRAM except that ia higher bandwidth, meaning greater speed. This is achieved by transferring data on the up and down tick of clock cycle. Maximum transfer rate to L2 cache is approximately 1064 Mbps for 133 MHz

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RDRAM:

Rambus DRAM is a radical departure from the previous DRAM architecture. It was designed by Rambus and uses a special high-speed data bus called Rambus channel to transfer data between memory and processor. RDRAM memory chips works in parallel to achieve a data rate of 800 MHz or 1600 Mbps.

DDR2:

DDR2 is the recent version of DDR SDRAM. It offers new features and functions that enable higher clock and data rate operations. DDR2 transfer 64 bits of data twice every clock cycle. However, a drawback of DDR2 is that it is not compatible with the DDR SDRAM memory slots.

VRAM:

Video RAM is a type of RAM which can be read from and written to at the same time. This is called dual-ported memory. On the other hand DRAM is single ported, which means that the memory can be written to and read from, but one at a time and not simultaneously. VRAM is most commonly used on video accelerator because it outperforms the other memory type by being dual ported.

Flash Memory:

Flash Memory is used to quickly store data from electronic devices such as digital cameras and MP3 players. Unlike DRAM or SRAM, data written to flash memory doesn't require power to maintain the stored contents.

Embedded Memory:

Embedded Memory is a small, dense format frequently used on electronic devices with small form factors, such as PDAs and cell phones. While limited in storage capacity when compared with DRAM modules used on personal computers, embedded memory plays a crucial role in many electronic devices due to its small size.

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Optical Memory:

In Optical Memory, data is stored on an optical medium (i.e., CD-ROM or DVD), and read with a laser beam. While not currently practical for use in computer processing, optical memory is an ideal solution for storing large quantities of data very inexpensively, and more importantly, transporting that data between computer devices.

ROM

ROM is a nonvolatile memory that is installed by the vendor of the computer during the process of manufacturing the motherboard or secondary components that need to retain the code when the machine is turned off.

With the use of ROM, information that is required to start and run the computer cannot be lost or changed.

ROM is used extensively to program operation of computers, as well as devices like cameras and controls for fuel injectors in modern cars.

In Computers ROM generally holds instructions for performing owner on Self Test (POST) routine, and the BIOS information used to describe system configuration

Types of ROMs

PROM EPROM EEPROM

PROM:

A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory. Such PROMs are used to store programs permanently. They are frequently seen in computer games or such products as electronic dictionaries, where PROMs for different languages can be substituted.

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PROM

EPROM:

An EPROM, or erasable programmable read-only memory, is a type of computer memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile normally used in electronic circuits. Once programmed, an EPROM can be erased only by exposing it to strong ultraviolet light.

EEPROM:

EEPROM such as Flash memory (Electrically Erasable Programmable Read-Only Memory) allow the entire ROM (or selected banks of the ROM) to be electrically erased (flashed back to zero) then written to without taking them out of the computer (camera, MP3 player, etc.).

Flashing is much slower (milliseconds) than writing to RAM (nanoseconds) (or reading from any ROM).

EPROMs are easily recognizable by the transparent window in the top of the package, through which the silicon chip can be seen, and which admits UV light during erasing.

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Memory Packaging

Memory is available in various physical packaging. Roughly in order of their appearance, the major types of packaging include:

DIP

SIPP

SIMM

DIMM

SODIMM

RIMM

Dual Inline Pin Package (DIP):

• Early versions of RAM were installed as single chips, usually 1-bit-wide DIP (dual inline package)

• To upgrade or add memory, new chips had to be individually installed on the motherboard (eight or nine chips per row—nine chips if using parity). This could be challenging, because each chip had 16 wires that needed to be perfectly aligned before insertion into the base.

Single in-line Pin Package (SIPP):

One of the first module forms of DRAM, the SIPP is a printed circuit board with individual DRAM chips mounted on it.

A few 80286-based computers used (often non-standard) memory modules like SIPP memory (single in-line pin package).

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SIPP's 30 pins often bent or broke during installation, which is why they were quickly replaced by SIMMs which used contact plates rather than pins.

Single Inline Memory Module (SIMM):

Used in personal computers. A 30-pin. The first variant of SIMMs has 30 pins and provides 8 bits of

data (9 bits in parity versions). SIMMs have 30 contacts in a single row along the lower edge A 30-pin SIMM can have as few as two or as many as nine individual

DRAM chips. The second variant of SIMMs—also called PS/2 has 72 pins and

provides 32 bits of data (36 bits in parity versions).

Dual Inline Memory Module (DIMM):

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A DIMM or dual in-line memory module comprises a series of random access memory integrated circuits.

These modules are mounted on a printed circuit board and designed for use in personal computers.

DIMMs began to replace SIMMs (single in-line memory modules) as the predominant type of memory module as Intel's Pentium processors began to control the market.

The main difference between SIMMs and DIMMs is that SIMMs has a 32-bit data path, while DIMMs have a 64-bit data path.

Small Outline DIMM (SODIMM):

Small outline DIMM (SO-DIMM). Smaller version of the DIMM, used in laptops. Comes in versions with 72 (32 bit), 144 (64 bit), 200 (72 bit) pins.

SO-DIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs. As a result SO-DIMMs are mainly utilized in laptops.

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Rambus Inline Memory Module (RIMM):

Direct Rambus DRAM or DRDRAM (sometimes just called Rambus DRAM or RDRAM) is a type of synchronous dynamic RAM, created by the Rambus Corporation.

The first PC motherboards with support for RDRAM debuted in 1999. They supported PC800 RDRAM, which operated at 800 MHz over a 16 bit bus using a 184 pin RIMM form factor.

High speed 1066, 800, 711 and 600 MHz RDRAM storage Overheating causes the problem of hanging.

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Memory Allocation

How the memory is allocated for use by the CPU is called memory mapping

It uses hexadecimal addresses to define ranges of memory. The original processors developed by Intel were unable to use more

than 1 MB of RAM, and the original IBM PC allowed only the first 640 KB of memory for direct use.

MS-DOS applications were written to conform to this limitation. The first 640 KB was reserved for the operating system and

applications (designated as conventional memory). The remaining 384 KB of RAM (designated as upper memory) was earmarked for running the computer's own housekeeping needs (BIOS, video RAM, ROM, and so on).

Memory Mapping:

Conventional (base) memory Upper memory area (UMA) Expanded memory

(become obsolete nowadays) High memory area (HMA) Extended memory (XMS)

Conventional Memory:

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Conventional memory is the amount of RAM, typically 640 KB, addressable by an IBM PC or compatible machine operating in real mode.

Conventional memory is located in the area between 0 and 640 KB. Without the use of special techniques, conventional memory

is the only kind of RAM accessible in DOS mode and DOS mode programs.

Upper Memory Area:

The upper memory area (UMA), the memory block from 640 KB to 1024 KB, is designated for hardware use, such as video RAM, BIOS, and memory-mapped hardware drivers that are loaded into high memory.

Expanded Memory:

Expanded memory can provide up to 32 MB of additional memory, and because it is loaded from a 64-KB section, it is below the 1-MB limit and therefore recognizable by MS-DOS.

MS-DOS applications must be specifically written to take advantage of expanded memory.

80386 and newer processors can emulate expanded memory by using memory managers such as EMM386.EXE and HIMEM.SYS.

High Memory Area:

An irregularity was found in the Intel chip architecture that allowed MS-DOS to address the first 64 KB of extended memory on machines with 80286 or faster processors. This special area is called the high memory area (HMA).

A software driver called an A20 handler must be run to allow the processor to access the HMA.

Extended Memory Specification (XMS):

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RAM above the 1-MB address is called extended memory. With the introduction of the 80286 processor, memory was

addressable up to 16 MB. Starting with the 80386DX processor, memory was addressable up to 4 GB. Extended memory is

Accessed through an extended memory manager (HIMEM.SYS).

Shadow RAM:

Many high-speed expansion boards use shadow RAM to improve the performance of a computer. Shadow RAM rewrites (or shadows) the contents of the ROM BIOS and/or video BIOS into extended RAM (between the 640-KB boundary and 1 MB).

This allows systems to operate faster when application software calls any BIOS routines. In some cases, system speed can be increased up to 400 percent.

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Memory Errors: Detection and Correction

Almost all computers check every memory bit at system startup to determine whether there are any memory errors. There are two methods available to detect and correct the memory errors. These are:

Parity checking Error-correction code (ECC)

Parity Checking:

In parity checking, the computer manufactures add an extra bit to each byte of memory. This additional bit is known as a parity bit and is used to check the integrity of data contained in the RAM. A parity bit can be either odd or even.

An even parity bit is set to 1 if the total count of 1s in the given set of bits is odd (making total count of 1s including parity bit to even). If the total count of 1s is even, the even parity bit is set to 0. On the other hand, the odd parity bit is set to 1 if the count of 1s in the given set of bit is even(making total count of 1s including parity bit to odd). If the total count of 1s is odd, the odd parity bit is set to 0.

Whether it is an odd or even parity bit, the algorithm to determine the memory error is same. The parity bit checks that if a given byte of memory has the right number of binary zeros and ones in it. If the count changes, your computer knows an error occurred.

However, remember that parity checking is only an error detection mechanism and not an error correction mechanism. And because of not having any error correction mechanism, the parity checking is rarely used in modern day memory modules.

Error-Correction Code (ECC):

A more sophisticated mechanism of error detection and also to remove such memory errors is the error-correction code (ECC) mechanism. The ECC mechanism works in conjunction with the memory controller.

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The ECC mechanism functions in the following way:

When a data is stored in memory, the controller using ECC mechanism calculates a code that describes the bit sequence of the data to be stored in the memory. This code is stored along with the unit of data.

When the unit of data is requested for reading, the memory controller again calculates the code for about-to-be-read data using the original algorithm.

The memory controller then compares the newly generated code with the code generated when the data was stored.

If the codes match, the data is free of errors and is sent. If the codes don’t match, there is an error in the data that is being read.

The memory controller then determines the missing or erroneous bits through the code comparison.

The memory controller then corrects the erroneous data using some kind of error correction algorithm built into ECC.

The ECC scheme requires extra bits per byte of storage to store the code that contains the bit sequence of data to be stored or to be read. ECC memory requires five extra bits to protect an 8-bit byte, six to protect a 16-bit word, seven to protect a 32-bit word, and eight to protect a 64-bit word.