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Basic Hardware Overview(Continued)

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Chipset

• Recall that the chipset divides the motherboard traffic into two main categories based on speed.

• The Northbridge (a.k.a. Memory Bridge or Memory Hub or Host Bridge) handles the faster traffic.

• The Southbridge (a.k.a. I/O Bridge or I/O Hub) handles the slower traffic.

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PCI-X

• The PCI bus connects to the Southbridge.

• But as devices required more speed than the PCI standard allowed, a faster version, PCI-X (Peripheral Component Interconnect eXtended) was developed by IBM, HP, and Compaq.

• Whereas PCI allows up to 532 MB per second, PCI-X allows up to 1.06 GB per second.

• PCI-X is backward-compatible, – You can install a PCI-X card in a PCI slot (it will operate at the

slower PCI speed).

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AGP• Another faster variation on PCI developed

specifically for displays is AGP, Accelerated Graphics Port. – Came out in 1997– It works with the Northbridge instead of the Southbridge.– It has a special slot (usually brown in color) – Various throughputs: 266 MB/s (1X), 533 MB/s (2X);

and 1.07 GB/s (4X). – Supports pipelining – transmitting many instructions

together instead of one at a time.

• Being replaced by PCI Express.

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AGP slot

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PCI Express

• PCI Express, PCI-E or PCIe • Introduced by Intel in 2004. • Built to be fast like AGP (faster actually) but general

purpose like PCI.• It has point-to-point rather than a (shared) bus structure.

And has full-duplex serial connections called lanes –up to 32 lanes.

• In PCIe 1.1 each lane carries 250 MB/s (per direction). • PCIe 2.0 supports 500MB/s and PCIe 3.0 supports 1GB/s

PER LANE.

Extended ≠ Express

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In addition to power, hard-drives will have a data connection — either the older PATA (Parallel Advanced Technology Attachment) or the newer SATA (Serial Advanced Technology Attachment)

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Floppy Disk Drive• Early storage in PCs was a removable magnetic

medium known as the floppy disk. • In the early to mid-80’s a standard computer had a

dual floppy drive, the drives were designated A and B – leaving the hard drive when it became standard with the letter C.

• Early on, floppy disks shrunk in size and gained in capacity but this stopped at 3-1/2 inch floppy disk with 1.44 MB of storage that is standard today. – But it has become standard to not have a floppy drive.

“a cable with a twist”

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CD ROM Drive• CDs (Compact Disks) are an optical medium of storage that

has become standard in PCs. • A standard CD has about a thousand times the capacity of a

floppy disk. • Originally CDs were Read Only (CD-ROM), written by the

manufacturer and useful as a software delivery system. • As the amount of data users wanted to be portable grew, a

recordable CD (CD-R) filled the void. But it had the limitation of being Write Once. Finally the rewritable CDs (CD-RW) became available.

• DVDs are similar to CDs but have higher capacity. • Blu-ray

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Keyboard

• With early computers inputting was done by plugging wires in boards or flipping switches or paper tape or punch cards. But the keyboard made data entry user friendly.

• PCs have always had generic connectors to plug in devices so that users could adapt them to various purposes, but the keyboard is so standard it soon had a designated connector and controller on the motherboard. – But more recently the keyboard has gone back to a

generic port – namely the USB, Universal Serial Bus.

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Mouse• The mouse was not a standard input device in early PCs.

(They were initially frowned upon by people who considered themselves serious computer users.)

• But the user friendly graphical user interface (GUI) approach made using a computer more palatable to most users, and it soon became standard with its own designated connector.

– Again the trend for devices becoming standard and having designated connectors has changed recently with the introduction of the USB (universal serial bus) and USB keyboards and USB mice.

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Displays• The earliest display devices were lights or light-

emitting diodes (LEDs). However, the binary output was difficult to read.

• The monitor was an early standard output device. Early monitors were monochrome Cathode Ray Tubes (CRTs) – the same basic technology as television (of the time).

• Liquid Crystal Displays (LCD’s) and other “flat panel” displays have been replacing CRT’s.

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Expansion Cards

• In order to make PCs customizable, they have expansion slots – places where extra circuit boards called expansion cards can be added.

• The video card – extra circuitry needed to interface with the monitor – added to the capability of PCs.

PCI slot, PCI card

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PCI, Peripheral Component Interconnect, is a card, a slot, a bus, and a set of standards. These standards include Plug-N-Play.

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NIC

• PCs were initially stand-alone devices. But networking proved to be important and then crucial. The PC’s expansion slots allowed a user to add a Network Interface Card (NIC) to allow the computer to exchange information with other computers. – But now this circuitry is often right on the

motherboard rather than placed on an expansion card.

Wireless NIC

• A Wireless NIC or WNIC

• Has an antenna and uses electromagnetic waves (somewhat like radio or non-cable television) to communicate information.

• Many use a PCI slot.

• Alternatively one can use a USB wireless adapter.

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Ports• Some history …• In addition to expansion slots which allowed one

to add circuitry to interface with peripherals, older PCs also had two standard interface paradigms that if a device could use these, additional circuitry was not needed. The device could just be plugged in.

• These places to plug theses devices are called ports and the two OLD standards developed are serial connection and parallel connection.

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Serial Communication

• A serial connection sends information over the line one bit at a time.

• While serial data can flow along a single wire, there’s more to communication than just flow of information. The two devices must agree to communicate, so there are additional wires needed.

• A generic serial connector is the DB connector. (DB – databus) .

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Serial Port

• The serial port is now pretty old and not found on all computers.

• An old device designed for the serial port may require an adapter.

Serial DB9 connectors

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DIN connector• A DIN connector is one that meets the DIN

standards.• DIN stands for Deutsches Insitut für Normung eV,

the German version of ANSI, a organization that determines standards.

• On PCs DIN connectors are often used for keyboard and mouse. They may also been seen on routers and switches.

• The DIN connector for keyboard and mouse are actually mini-DIN connectors with 6 pins. The port was developed by IBM and is called PS/2.

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DB-9• The standard serial connector is called the DB-9.

Three pins are used for data (receiving and transmitting and ground) the rest are for control.

1. Carrier Detect – Is modem connected to a working phone line. 2. Receive Data - Computer receives information from modem. 3. Transmit Data - Computer sends information to the modem. 4. Data Terminal Ready - Computer tells the modem that it is ready 5. Signal Ground - Pin is grounded. 6. Data Set Ready - Modem tells the computer that it is ready to talk. 7. Request To Send - Computer asks the modem if it can send data. 8. Clear To Send - Modem tells the computer that it can send data. 9. Ring Indicator - Once a call has been placed, computer acknowledges

signal (sent from modem) that a ring is detected.

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Parallel Communication• A parallel connection sends many bits in parallel.

The original advantage of this is that it is faster, but the disadvantage is that it is more complicated to do.

• Parallel connections were used most often for printers and removable storage drives, which needed more speed than serial peripherals (e.g. a keyboard).

• Advances in serial connections (USB) have made them competitive with parallel connections. And devices such as printers conventionally thought of as strictly parallel devices are no longer thus.

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Parallel Port

• The parallel port is used along with a local communication standard that transmits 8 bits (a byte) at a time.

• Pins 2-9 and 18-25 carry the data (full duplex). Other pins control.

• The parallel-port standards are known as Enhanced Parallel Port (EPP) for non-printing devices and Extended Capabilities Port (ECP) for improved printing.

Female parallel port connector

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USB

• Universal Serial Bus (USB) is an attempt to have a universal port – a port which has reasonable speed, which many different devices can use at the same time, and which does not require expansion cards.

The USB A connector which plugs into the computer

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A USB socket in the back of the computer. Many computers have USB ports in the front. Some users are confused about the number of USB ports they have – assuming the front and back ports are distinct.

(Some monitors have USB ports.)

The USB B connector plugs into the device — distinct from the USB A connector that plugs into the computer.

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Connecting a USB device

• Connecting devices that use the old serial port, parallel port or an expansion slot require the system to be shut down, the device connected and then the system restarted.

• USB devices can be added while the system is up. This is known as hot plugging or hot swapping. – Distinct from Plug-N-Play (PNP) which is an

older standard.

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Up to 127 devices

• The USB standard supports up to 127 devices.

• A typical PC has one of two USB ports, one can connect more USB devices than there are USB ports by using USB hubs or daisy chaining.

USB hubs may or may not need their own power depending on the needs of the devices plugged into them

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USB Cable

• A USB connection is simpler hardware than a standard serial connection using a DB9 connector. – It has two wires for power : +5 volts and ground. So

devices that don’t require much power (e.g. a webcam) do not need an independent power source.

– It has a twisted pair of wires for carrying the data.

– Why is it twisted?

USB3 (aka SuperSpeed USB)

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USB3 (Cont.)

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Enumeration

• The PC must detect all of the USB devices and assign them addresses. This is known as enumeration.

• The PC also determines the manner in which it will exchange data with the device. – Interrupt: small amounts of data at intermittent times

– Bulk: larger chunks of data with error detection

– Isochronous: real-time stream of data without error detection

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Fire Wire

• The IEEE 1394 standard is for a fast serial cable that allows up to 63 devices to attach to a single port.

• Its high speed and isochronous data transfer make it useful for real-time data streaming.

• It supports Plug-and-play and hot plugging. • Originally developed by Apple and known as

firewire. Other companies have other names including Lynx and i.link.

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Fire Wire Connector

The standard supports a set of cables that have varying numbers of pins.

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RJ11 vs RJ45• The plugs used are the RJ-11 (modem) and the RJ-

45 (Ethernet NIC)• Both use Unshielded Twisted Pair (UTP) wires.

– Twisting reduces interference or cross-talk.

– Shielding would reduce it more but is more expensive.

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RJ-45

• Registered Jack-45, an eight-wire connector used to connect computers to an Ethernet LAN using UTP wire.

• RJ-45 connectors look similar to the RJ-11 connectors that are used for phones and modems, but RJ-45s are wider. – Additionally there are two sockets associated

with an internal modem.

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Modem with socket for two RJ-11 plugs.

UTP Ethernet connection with one RJ-45 plug.

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System Resources• System Resources are the logical/software way to

access various devices. It is a level above the hardware but intimately connected to it – as it helps the processor to locate and interface with the hardware.

• Data is transmitted between the processor and devices using various shared communication channels (the buses). Thus an addressing scheme is required to determine where data is coming from or where it is going, which device is seeking the attention of the processor, and so on.

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System Resources (Cont.)

• I/O Addresses: processor talks to device

• IRQ: device tells processor it requires attention

• DMA: device interacts with memory without bothering processor

• Memory Addresses: portion of memory allocated for device instructions

Device Manager – Once place to look at System Resources

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Resource Conflicts

• Addresses must be unique if they are to be used to distinguish various devices.

• If two devices claim the same resource, there is said to be a conflict.

• Certain well established devices use a set IRQ. • Plug-n-Play (PnP) has eliminated a lot of

conflicts since the system assigns its own resources to the devices.

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No conflicts

Advanced System Information – Another place to look at resources

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Forced hardware

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I/O addresses

• Every PC device has an Input/Output (I/O) Address or port address.

– Standard devices have standard I/O addresses.

– These I/O addresses and the memory locations they represent are like mail boxes for devices. Data for a device is sent to that devices I/O Address (mailbox).

– It is also a way to control devices, certain addresses correspond to specific actions of the device.

• This scheme of associating memory locations with devices is known as memory-mapped I/O.

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Keyboard’s I/O address range

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A different view of the Device Manager

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Resources by type view (I/O)

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Requesting an interrupt

• Devices cannot get the immediate attention of the processor. Instead the device makes an interrupt request.

• The processor only allows itself to be interrupted at certain times.

• All devices interrupt the processor in the same way, the processor must then trace back to find out which device requested the interrupt.

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IRQ• Devices that interrupt the processor are assigned

an IRQ (Interrupt Request Line).

• Typically a device has a set IRQ or finds an available IRQ, occasionally two devices want the same IRQ and a conflict arises. Older versus newer IRQ

• Older IRQ allowed only up to 16 addresses IRQ lines. The newer version uses IOAPIC – I/O Advanced Programmable Interrupt Controller – and allow for more IRQ lines.

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IRQs in Device Manager

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DMA

• Normally a device interacts with memory (reads or writes data) via the processor.

• A Direct Memory Access (DMA) channel allows a device to interact with memory without going through the processor. This speeds up data transfers.

• There are usually fewer conflicts over DMA than over IRQ.

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Floppy Resource with DMA

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Resources by type view (DMA)

DMA Use

• The DMA System Resource is about devices that need a DMA controller as opposed to having their own circuitry for managing memory access.

• More devices use DMA than it looks like.

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COM Port

• The term COM (communications) port is sometimes used instead of serial port.

• COM corresponds to a set of addresses (software instead of hardware) that is associated with the serial port. – In particular COM1 corresponds to IRQ 4 and

I/O address 03F8

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To look at or change port information, right click on My Computer, choose Properties, go to the Hardware tab. Click on Device manager. (XP)

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Expand the ports item and double click on the port – COM1 in this example. (XP)

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Port Properties dialog boxes.

Look at options for Port Settings.

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LPT

• The term LPT (Line Printer Terminal) port is sometimes used instead of parallel port.

• Like the term COM, LPT corresponds to a set of addresses (software instead of hardware) this time associated with the parallel port. – In particular LPT1 corresponds to IRQ 7 and I/O

address 0378

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Logical device names• The COM and LPT ports can be located using the

various addresses associated with them. However, they can also be referred to by using their name COM1, COM2, LPT1 or LPT2.

• This logically higher naming scheme (known as the logical name) allows these ports to be found even without knowing their assigned I/O addresses and/or IRQ.

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Memory Addresses and BIOS shadowing• There is some (ROM) BIOS associated with each device

that holds the lowest-level instructions that the PC cannot forget in order to operate.

• But main memory (RAM) is faster than ROM, so commonly used, but slow parts of the BIOS are placed in memory to improve speed. This is known as BIOS shadowing.

• A device’s Memory Range are memory locations associated with a device to hold its shadowed BIOS. They are placed in what is called “upper memory.”

• (Strictly speaking not a system resource.)

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Memory Range for NIC

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Resources by type view (Memory)

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Plug-and-Play

• System configuration (adding cards, assigning resources used to be technical and tedious). Most modern operating systems support Plug-and-Play (PnP).

• With PnP, system resources are assigned automatically and in most cases, conflicts are avoided.

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References• http://pcguide.com/ref/index.htm • http://computer.howstuffworks.com/usb.htm • http://computer.howstuffworks.com/parallel-

port.htm • http://computer.howstuffworks.com/serial-port.htm • http://en.wikipedia.org/wiki/

Northbridge_(computing)• www.intel.com/technology/pciexpress/devnet/

docs/WhatisPCIExpress.pdf

References (Cont.)

• http://www.webopedia.com

• http://www.whatis.com

• PC Hardware in a Nutshell, Thompson and Thompson

• A+ Certification: Exam Guide, Meyers and Jernigan

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