Chapter 9 External Hardware Interfaces Graymark DFnDR Trainer 9-1 INTRODUCTION Many devices are available for external connection to computers. These devices include: • Hard Drives• Optical Drives• Tape Drives• Memory Cards• USB Drives• Printers• Scanners • FAX MachinesTo enable communication between an external device and a computer, there must be two key elements: • Hardware interface• Software interfaceThere are several popular hardware interfaces. Each hardware interface typically has a corresponding software interface. The hardware interfaces include: • USB (Universal Serial Bus)• FireWire (IEEE 1394)• Parallel PortChapter 9 ExternalHardwareInterfaces KNOWLEDGE OBJECTIVES After you successfully complete this chapter you will have the knowledge to: 1. List the different type of external hardware interfaces 2. Explain the USB standards 3. Describe the FireWire standards 4. Identify parallel ports and cable c onnectors 5. Distinguish a SATA port from an eSATA port 6. Recognize an infrared port Chapter 9 External Hardware Interfaces 9-2 Graymark DFnDR Trainer • eSATA (External SATA)• InfraredUNIVERSAL SERIAL BUS Universal Serial Bus (USB) is a serial communication hardware interface. USB devices are connected through various devices, including: • USB hub• Keyboard hub• Monitor hub• Computer motherboardA USB system needs a host, in either the computer or USB hub. According to the USB rules, only one host is allowed on the USB bus. USB is designed to support low-speed peripheral devices such as: • Keyboards• Mice• Printers• Scanners• Modems• Network Interface Controllers (NICs)
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INTRODUCTIONMany devices are available for external connection to computers. These devices
include:• Hard Drives
• Optical Drives • Tape Drives
• Memory Cards
• USB Drives
• Printers
• Scanners
• FAX Machines
To enable communication between an external device and a computer, there must
be two key elements:• Hardware interface
• Software interface
There are several popular hardware interfaces. Each hardware interface typically
has a corresponding software interface. The hardware interfaces include:• USB (Universal Serial Bus)
• FireWire (IEEE 1394)
• Parallel Port
Chapter 9ExternalHardwareInterfaces
KNOWLEDGE OBJECTIVESAfter you successfully complete this chapter you will have the knowledge to:
1. List the different type of external hardware interfaces
2. Explain the USB standards
3. Describe the FireWire standards
4. Identify parallel ports and cable connectors
5. Distinguish a SATA port from an eSATA port
6. Recognize an infrared portChapter 9 External Hardware Interfaces
9-2 Graymark DFnDR Trainer• eSATA (External SATA)
• Infrared
UNIVERSAL SERIAL BUSUniversal Serial Bus (USB) is a serial communication hardware interface. USB
devices are connected through various devices, including:• USB hub
• Keyboard hub
• Monitor hub
• Computer motherboard
A USB system needs a host, in either the computer or USB hub. According to theUSB rules, only one host is allowed on the USB bus. USB is designed to support
ICON The icon used to identify USB connectors and devices is shown in Figure 9-1.
Figure 9-1. USB iconUSB 1.1 The USB 1.1 standard was developed by Compaq, DEC, IBM, Intel, Microsoft,
NEC, and Northern Telecom. The primary goal was to provide a seamless way for
computer users to connect devices. The goal was to develop a true plug-and-play
system without requiring a computer user to upgrade internal components of the
computer system.
The USB bus supports digital video standards MPEG-1 and MPEG-2. USB
transfers data at a rate of 12 Megabits per second for the USB 1.1 standard. USB
1.1 can support up to 127 USB devices. Device speed will vary from 1.5 MB/sec
to 12 MB/sec. The lower rate is intended for input devices such as mice and
keyboards. The high-end rate of 12 MB/sec is intended for storage devices, as
well as video and audio devices.
The USB 1.1 standard allows hot pluggable or hot swapping. This means that aUSB device can be installed or detached without powering OFF the computer.Chapter 9 External Hardware Interfaces
Graymark DFnDR Trainer 9-3
Plug-and-play is supported through appropriate USB device drivers via the
operating system or manufacturer.
The USB bus is self-powered or powered through a USB hub supplying between
100 mA and 500 mA of current. A self-powered USB bus is the type found in a
computer system.
USB 2.0 The USB 2.0 standard transfers data at rates of 480 MB/sec. USB 2.0 is also
designed to be downward compatible with USB 1.1 devices.
USB HUB A USB hub allows several USB devices to be connected to one USB computer
port. A USB hub has peripheral ports to which external devices can be connected
The number of peripheral ports on a hub can vary from two to 16. A 4-port USBhub is shown in Figure 9-2. Figure 9-2. 4-Port USB hub
DATATRANSMISSIONData flowing from the device to the host is called upstreaming. Data flowing from
the host to the device is called downstreaming. The host, whether it is a USB hub,
motherboard USB host, or USB expansion card, is connected electrically through
wires.
CABLES &
CONNECTORSA USB 1.1 standard cable is 20 AWG, shielded, twisted-pair (STP), four
conductors (2 pairs). The maximum cable length between devices cannot exceed 5
meters (16 feet).
There are two USB connector types:• Type A
• Type B
There are also three sizes of USB connectors:• Standard
TYPE AThe Type A connector is used on computers or other hosts. This connector is
thinner and wider than Type B; it is more rectangular than Type B. A Type A port
and cable connector are shown in Figure 9-4 and Figure 9-5. Figure 9-4. USB Type A port
Figure 9-5. USB Type A cable connector
TYPE BThe Type B connector is used on peripheral devices such as printers. This
connector is thicker and narrower than Type A; it is more square than Type A. A
Type B port and cable connector are shown in Figure 9-6 and Figure 9-7.Chapter 9 External Hardware Interfaces
Graymark DFnDR Trainer 9-5
Figure 9-6. USB Type B port
Figure 9-7. USB Type B cable connector
Some manufacturers alternatively use the terms Series A and Series B.Upstream connectors are Type B, and downstream connectors are Type A.
Microsoft specifies that computers sold with Windows must have at least four
externally accessible USB ports.
MINI USB CONNECTORSAs the need for smaller connectors emerged, a Mini USB connector was
developed. A Mini USB cable connector is shown in Figure 9-8. Figure 9-8. Mini USB cable connector
MICRO USB CONNECTORSEven smaller on-the-go demanded USB connectors that were smaller than theMini USB. The Micro USB connector, shown in Figure 9-9, is smaller than the
Mini USB connector.Chapter 9 External Hardware Interfaces
9-6 Graymark DFnDR Trainer
Figure 9-9. Micro USB cable connector
OPERATINGSYSTEM SUPPORTNot all operating systems will fully support USB. In other words, all operating
systems are not fully compatible with USB. The operating system, motherboard
BIOS, and motherboard chip set must all support USB for the best performance.
Windows 95 OSR 2.1 offered limited support for USB. Windows 98, Windows
XP, Windows 2000 and MAC OS 8.1 offer expanded support for USB and USB
devices.
INTRODUCTION In this exercise, you will examine USB connectors and cables.
The parallel interface uses a large number of connections. The minimum number
of wires in a parallel interface cable is 18. A thick cable is used to connect printers
and other parallel devices to a computer.
DB-25 CONNECTORThe parallel port connector on a computer is a 25-pin female D type connector,
commonly referred to as a DB-25 connector. The female DB-25 computer
connector is shown in Figure 9-15. Figure 9-15. DB-25 female connector on computer
A parallel cable is used to connect a device with a parallel interface to a computer.
The end that connects to a computer is a male DB-25 connector. This cable
connector is shown in Figure 9-16. Figure 9-16. DB-25 male cable connector
Chapter 9 External Hardware Interfaces
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The other end of a parallel cable will have one of two different connectors:• DB-25 male
• Centronics
CENTRONICS CONNECTOR
The first printer with a parallel interface was manufactured by Centronics. Theyinstalled a 36-pin connector on the printers. Since Centronics designed the
connector, it was, and still is, referred to as a 36-pin Centronics connector. A
drawing of the 36-pin Centronics cable connector is shown in Figure 9-17. Figure 9-17. 36-Pin Centronics cable connector
INTRODUCTION In this exercise, you will examine parallel ports and cables.
INVESTIGATIONCOMPUTER SETUPNone.
PROCEDURE 1. Retrieve the following items:• Parallel Cable from FRED Large Cables Storage Container
2. Examine the Parallel Cable from the FRED Large Cables Storage Container.
Identify the Parallel Connectors.It has a DB-25 male connector on one end and a 36-pin Centronics
connector on the other end.
3. Examine the back of the Desktop Evidence Computer. Identify the
Parallel Connector.
It has a DB-25 female connector.
EXERCISE 9.3 - EXAMINE PARALLEL CABLES & PORTS
SKILL OBJECTIVESAfter you successfully complete this exercise you will have the skills to:
1. Identify the parallel ports and cable connectorsChapter 9 External Hardware Interfaces
Graymark DFnDR Trainer 9-13INSTRUCTOR’S EVALUATIONYour instructor will evaluate and grade your work in this exercise.
COMMENTS
INITIALS: __________ DATE: __________
eSATAIn 2004, a modified version of the SATA hard drive interface was developed for
The hard disk drive is sealed when manufactured. The disks/platters spin at a rate
of 5400 rpm or more. The read/write heads do not touch the platters; they “fly”
over the platters at a height of only 2 to 3 micro inches. (A human hair is 3000
micro inches thick) If the drive is opened, any dirt or dust will damage the heads
and also will cause physical damage to the platters.
PLATTER Depending on the hard disk drive size, the drive can have one or more platters
encased in the housing. The platter consists of an aluminum disk coated with a
highly polished magnetic media.
FORMATTINGA new hard drive is not formatted. Prior to installing an operating system, a
partition must be created using the FDISK utility. It must then have a high levelformatting using the DOS FORMAT command.
After formatting, the platters are divided into tracks and sectors, as shown in
Figure 10-3. A sector is the smallest addressable area on the hard disk drive. A
sector is usually 512 bytes. Figure 10-3. Disk & sector layout
HARD DRIVE CYLINDERA track on a hard disk drive is referred to as a cylinder. The cylinder is comprisedof all the tracks located in the same physical area on all the platters. The read/
write heads read from and write to these areas at the same time.
SKEWINGAs the read/write heads move to an adjacent cylinder to continue a read or write
operation, it often misses the proper track. The heads must wait until the data track Chapter 10 Hard Disk Drives
Graymark DFnDR Trainer 10-5
they are seeking returns on the next revolution. Although the wait time may seem
miniscule, the time accumulated over thousands of revolutions would
significantly slow the read/write process if engineers had not built in
compensating designs.
Track SkewingTrack skewing is a method in which the read/write heads read or write data to
multiple platters at the correct timing interval. The platters are designed so when
data located in track 1, sector 8 on platter 1 has been read, data located in track 1,
sector 8 on platter 2 is in position to be read. This is illustrated in Figure 10-4. Figure 10-4. Track skewing
Cylinder SkewingCylinder skewing is utilized to change from cylinder to cylinder without waiting
for the platter to make one revolution. When cylinder 1, sector 8 of platter 1 has
been read, cylinder 2, sector 1 is ready to be read, as shown in Figure 10-5. Figure 10-5. Cylinder skewing
Both track and cylinder skewing are functions controlled by the ROM. Current
hard disk drives are considered high-density drives. The magnetic media that is
distributed on the aluminum platter is of very high coercivity. This allows more
CABLES & CONNECTORSIDE was a major change in the drive electronics. The electronic interface circuitry
was integrated into the hard drive. The IDE drive has two connectors and a
header:• Power Connector, 4-Pin
• Data Connector, 40-Pin• Drive Select Header
POWERThe power connector is a 4-pin connector. This connector is also referred to as a
Molex connector. Molex is the connector manufacturer.
The DC power connector supplies power to the hard disk drive. DC voltage used
by the hard disk drive is 12 VDC, 5 VDC and common.
Refer to Figure 10-6 to identify the male connector used on the hard drive. The
power connector on the power supply cable is a female connector, as shown in
Figure 10-7. Figure 10-7. 4-Pin connector on power supply cable
DATA
IDE / ATA hard drives incorporate a parallel data connection. This parallelconfiguration requires a 40-pin data connector. A single 40-pin cable connects the
drive to an IDE controller card or the motherboard if it has an onboard IDEChapter 10 Hard Disk Drives
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controller. Integrating the electronics directly to the drive enhances the drive’s
performance.
Refer to Figure 10-6 to identify the male data connector used on the hard drive.Figure 10-8 shows an IDE data cable. Figure 10-8. IDE data cable
DRIVE SELECT HEADERRefer to Figure 10-6 to identify the male drive select header on the hard drive.
This header is used to select one of several operational functions:• Master - configures the drive as the primary boot drive
• Slave - used if a second drive is connected to the same IDE cable
• Cable Select - allows the BIOS to determine if the drive is the primary boot drive
• Slave Present - used if the drive will be used as a slave drive when the primary drive
is set for Cable select
HEADERS & JUMPERSHard drives, motherboards and many other computer devices may have several
open-frame pin connectors called headers. Each header is used for one of two
different functions:• Connect other computer components to the motherboard • Serve as a switch
Headers are available in different sizes, such as 2-pin, 3-pin, 4-pin, etc. Typical 2-
pin and 3-pin headers are shown in Figure 10-9. Figure 10-9. Typical 2-pin & 3-pin headers
Headers Used as ConnectorsHeaders that are used to connect components together function the same as other
electrical connectors. A wire or cable to be connected to a motherboard or other
component will have a plug on the end of the wire or cable. The plug will be
mated with the motherboard or other component to connect the two components.Chapter 10 Hard Disk Drives
Headers Used as SwitchesHeaders that function as switches use a special connector plug called a shorting
jumper or jumper. Figure 10-9 illustrates a 2-pin jumper. The jumper can connect
two adjacent header pins together.
Together, a header and jumper operate like a switch to select different modes of
operation. Figure 10-10 illustrates a jumper used to select a function by
connecting pins 1 and 2 together. Figure 10-10. Header and jumper used as a switch
If a jumper is placed on two adjacent header pins, the switch is closed. If the same
two header pins do not have a jumper, the switch is open. Jumpers are removable
and reusable, and can be used on different components.
As shown in Figure 10-11, jumpers are comprised of two pieces:• Plastic body
• Shorting strip
Figure 10-11. Jumper construction & installation
Figure 10-11 also shows how to use long nose pliers to install and remove a
jumper from a header.
When a jumper is removed from a header, the shorting strip may remain attached
to the header; with only the plastic body removed. If this happens, the header pinsremain connected or closed. After you remove a jumper, always check to makesure the shorting strip is inside the plastic body.
If the shorting strip is not in the plastic body, it is probably still on the header.
Carefully remove the shorting strip with a small pair of pliers. The shorting strip
can then be reinserted into the plastic body.Chapter 10 Hard Disk Drives
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IDE BUS VERSIONSThe IDE interface is available in several different configurations:• XT IDE (8-bit)
• AT Attachment (ATA)
• IDE (16-bit)
• MCA IDE (16 bit Micro-Channel)
EXTENDED TECHNOLOGY (XT)The XT has an 8-bit bus that uses a 40-pin interface cable.
ADVANCED TECHNOLOGY ATTACHMENT (ATA)The ATA uses a 40-pin interface cable.
INTEGRATED DRIVE ELECTRONICS (IDE)The standard IDE has a 16-bit bus.
MICRO-CHANNEL ARCHITECTURE (MCA)The MCA has a 16-bit architecture and uses a 72-pin interface cable.
EIDE An improved version of IDE is the Enhanced Integrated Drive Electronics (EIDE)
drive. Unlike IDE drives, the EIDE drive protocol doesn’t require much CPU
processing time. EIDE hard drives must work with an EIDE hard drive controllerfor best performance.
EIDE INTERFACEATA-2 or EIDE (Enhanced IDE) is an extension of the original ATA that includes
features such as PIO (programmed I/O) and DMA modes. These are basically
performance enhancing features.
The main benefits of ATA-2 are twofold:• Increased capacity due to an advance in BIOS to work with drives larger than 504
ATAPI ATA Packet Interface (ATAPI) is one of most common standards found on IDE/
EIDE drives, as well as CD-ROM and internal ZIP drives. ATAPI is interface
hardware that is located on the drive’s electronic circuit board. With an ATAPI
interface in place, the drive does not need a software driver.Windows 9X, Windows NT, Windows 2000, Windows ME, Windows XP and
Linux all support the ATAPI interface. If a drive needs to operate in a DOSenvironment, however, then separate software drivers have to be installed.
SATA The original Advanced Technology Attachment (ATA) protocol uses a 40-wire
parallel data interface. The parallel ATA system was modified to create the Serial
Advanced Technology Attachment (SATA) protocol.
Transfer rates for Serial ATA begin at 150MBps. The thinner ATA serial cables
also allow a more efficient airflow inside a computer. Serial ATA cables can be as
long as one meter. A typical SATA drive is shown in Figure 10-12.Chapter 10 Hard Disk Drives
Graymark DFnDR Trainer 10-11
Figure 10-12. Typical SATA hard drive
CABLES & CONNECTORSThe SATA system employs a 4-wire serial connection to the computer. SATA datatransfer rates are faster that ATA rates. There are four varieties of SATA
connectors:• Standard
• Slimline
• Micro
Standard The Standard SATA cable is used on standard SATA hard drives. The connector
has 22 pins:• 7 pins for data
• 15 pins for power
A close up of the SATA hard drive connectors is shown in Figure 10-13.
Chapter 10 Hard Disk Drives10-12 Graymark DFnDR Trainer
Figure 10-13. SATA drive connectors
SlimlineThe Slimline SATA cable is used on Slimline SATA hard drives. The connector
has 13 pins:• 7 pins for data
• 6 pins for power
MicroThe Micro SATA cable is used on 1.8” SATA hard drives. This connector has 16 -
pins:• 7 pins for data
• 9 pins for power
DATASATA drives can be easily distinguished from ATA drives by observing the data
connector or cable. ATA cables are very wide, while SATA cables are very
narrow, as shown in Figure 10-14. The SATA cable is on the left, and the IDE
cable is on the right. Figure 10-14. SATA & IDE (ATA) data cables
POWERSATA drives may have one of three different power connectors:
IDE (ATA) power cable connectors cables have 4 large pins, while SATA power
cable connectors have 15 small pins, as shown in Figure 10-15. The SATA powercable connector is on the left, and the IDE (ATA) power cable connector is on the
right. Figure 10-15. SATA & IDE (ATA) power cable connectors
SATA IISATA II drives have the same interface and other physical characteristics. The
primary difference is that the SATA II has a much faster data transfer rate.
INTRODUCTION In this exercise, you will examine various hard drives to identify characteristics
that differentiate the types of hard drives.
INVESTIGATIONCOMPUTER SETUP1. If Windows is not already running, boot to Windows.
2. Be sure that you are logged on as the User.
PROCEDURE 1. See your instructor for the procedure.
EXERCISE 10.1 - IDENTIFY DIFFERENT TYPES OF HARD
DRIVES
SKILL OBJECTIVESAfter you successfully complete this exercise you will have the skills to:
1. Identify different types of hard drives
NOTE
This is an optional exercise. Your instructor will advise you of the procedure.Chapter 10 Hard Disk Drives
10-14 Graymark DFnDR Trainer
INSTRUCTOR’S EVALUATIONYour instructor will evaluate and grade your work in this exercise.
COMMENTS
INITIALS: __________ DATE: __________
IMAGE DRIVEYour Trainer includes a SATA Hard Drive. You will use this SATA Drive to
capture images from evidence devices. Since it will be used to capture images, it
will be referred to as your Image Drive.
To protect your Image Drive, you will mount it in a mobile hard drive rack. A
mobile hard drive rack is an external hard drive housing. The rack provides
physical and electro-static protection for a hard drive.Like hard drives, mobile racks are available for different sizes and types of hard
drives. Your Mobile Rack, shown in Figure 10-16, is a 3.5” SATA type to match
your 3.5” SATA Image Drive. RATINGPoor Good ExcellentITEM 1 2 3 4 5Followed InstructionsCompleted WorkThorough & ClearAccurate GRADETOTAL + + + + =
13. Using the four Screws provided with the Mobile Drive Rack, secure the
Hard Drive to the Drive Tray, as shown in Figure 10-24. Do not
overtighten the Screws. Figure 10-24. Securing Hard Drive to Drive Tray
14. Turn the Drive Tray over.
15. As shown in Figure 10-25, replace the Metal Cover on the Drive Tray. Be
sure it snaps into place.Chapter 10 Hard Disk Drives
Graymark DFnDR Trainer 10-19
Figure 10-25. Replacing Metal Cover on Drive Tray
16. Position the Drive Tray in front of the Mobile Drive Rack, as shown in
Figure 10-26. Figure 10-26. Positioning Drive Tray and Rack
17. Slide the Drive Tray into the Rack.
18. Carefully close the hinged Access Door. As you close the Door, the Drive
Tray will be moved further into the Rack. The Hard Drive Connectors
will be mated with the Mobile Drive Rack Connectors.
19. Close the Latch.
INSTRUCTOR’S EVALUATIONYour instructor will evaluate and grade your work in this exercise.RATINGPoor Good ExcellentITEM 1 2 3 4 5Followed InstructionsCompleted WorkThorough & ClearTOTAL + + + + =
Chapter 10 Hard Disk Drives
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COMMENTS
INITIALS: __________ DATE: __________
SCSI The Small Computer System Interface (SCSI) is a high performance disk driveinterface system. SCSI drives require a special I/O controller board. SCSI is
pronounced “skuzzy”. The interface can access up to seven hard disk drives.
SCSI INTERFACESCSI is a system level interface. A SCSI device can be a CD drive, hard disk
drive, scanner or other device. The SCSI system requires a host adapter thatinterfaces with other devices. SCSI allows for a mix of different SCSI devices. All
of the devices attached to the host adapter are part of the SCSI bus.
A typical computer system can support up to four SCSI buses. Each SCSI bus can
support up to seven devices plus the host adapter for a total of 28 SCSI devices.
THROUGHPUTThe throughput of newer SCSI host adapters can be 160 MB/sec or more and are
capable of supporting up to 15 devices per channel using 32-bit host adapters. Thehost adapter can be plugged into an EISA, ISA or PCI expansion slot, or
integrated onto the motherboard.
DATA TRANSFER RATESThe current SCSI standards include:• Standard SCSI (SCSI-1)• Fast SCSI or Fast Wide SCSI (SCSI-2)
The internal cable that SCSI uses is a flat ribbon cable with either a 50 or 68-pin
interface. SCSI cables are either type A or type P.• Type A is a 50-pin cable and cannot exceed 6 meters (nearly 20 feet)
• Type P is a 68-pin cable that cannot exceed 3 meters (nearly 10 feet)
External CablesThere are several external SCSI cables available. They have different
combinations of connectors.
Figure 10-27 illustrates a SCSI cable with a 50-pin connector at one end and a 68-
pin connector on the other end. In Figure 10-27, the 50-pin connector is on the leftside, and the 68-pin connector is on the right side. Figure 10-27. SCSI cable connectors
TerminatorsOn the SCSI bus the first and last SCSI device on the bus must be terminated. The
host adapter and internal SCSI devices have a built in termination. Depending on
the SCSI device, it may have one of three types of terminating devices: Passive,
Active, and Forced Perfect Termination.• Passive Termination - A network of resistors (used in Normal SCSI)
• Active Termination - uses voltage regulators to ensure the termination voltage is
SCSI TYPESSCSI is also identified as either single-ended SCSI (normal) or differential SCSI.
Each type can be identified by its own symbol located on the SCSI device. See
Figure 10-29 for the SCSI symbols.
Single-ended and differential SCSI devices cannot be mixed on a single SCSI bus. Figure 10-29. Single-ended and differential SCSI universal symbols
Single-Ended SCSI Single-Ended SCSI is so named because for every electrical signal that is
transmitted, a single wire must exist for the signal to travel on.
Differential SCSI
Differential SCSI uses two wires for the signal to travel on. This two-wireinterface makes the Differential SCSI less prone to noise and interference.
CONFIGURING SCSIChapter 10 Hard Disk Drives
Graymark DFnDR Trainer 10-23
Refer to Figure 10-30 for the following discussion. Although SCSI configuration
is a little more complex, SCSI devices have to be configured just as with IDE type
drives. The host adapter card is the first thing to be installed and configured. Each
SCSI device is then set with a unique ID number (1 through 7 or greater per bus)
through jumpers or switches on the device.
The last device on the SCSI bus is terminated. Each device is then added, one by
one, to the SCSI host adapter. If needed, a driver or software is loaded so the
system can recognize and access the device. Figure 10-30. Typical SCSI hookup diagram
External SCSI devices will have an input and output port. An external terminating
resistor is attached to the output port of the last device in the chain.
SCSI IDUp to seven SCSI devices plus the host adapter can be attached on a single SCSIbus. A unique identification number called the SCSI ID must be used to identify
each device. SCSI ID numbers are from 0 through 7.
The host adapter is configured for SCSI ID 7 (highest priority ID). Older adapter
cards required you to set SCSI IDs in sequence from that point (6, 5, 4, etc.)
Newer SCSI adapter cards can use an ID in any sequence as long as the ID does
not conflict with anything else on the SCSI bus. Read the manufacturer’s
information about the exact location of the SCSI ID jumpers.SCSI RULES• Both ends of the SCSI bus must be terminated
• Set the device to a unique, non-conflicting, ID number. The host adapter will usually
be set for ID 7 while other devices in the chain are set in descending order (older
cards) or any order (newer cards)
Chapter 10 Hard Disk Drives
10-24 Graymark DFnDR Trainer• If you are configuring SCSI hard drives, the drive must be partitioned and formatted
A SCSI drive with a 68-pin data connector is shown in Figure 10-31. Figure 10-31. Typical SCSI hard drive
SOLID STATE A solid-state drive (SSD) does not have platters or any moving parts. It uses flash
type memory. Some SSDs use SRAM or DRAM instead of flash memory. This
type of solid state drive is usually referred to as a RAM Drive.An SSD acts like (emulates) a hard drive. This makes it very easy to replace a
hard drive with an solid state drive. Because an SSD has no moving parts, it ismuch more rugged than hard drives.
HARD DRIVE OPERATIONThere will be occasions when the digital forensics examiner must understands
how a hard drive operates. This can be the case when there is difficulty reading a
hard drive, or when the examiner must testify about a hard drive’s operation.
STANDARD CHS Standard CHS (Cylinder Head Sector) is also called Normal. Standard CHS
limits
the drive to addressing 16 heads and 1,024 cylinders, which would give a
maximum capacity of 504 MB.
EXTENDED CHS Extended CHS is also referred to as Large. When chosen, a translated logical
geometry is used to communicate between the drive and BIOS. In order to displaythe logical drive parameters, divide the cylinder count by 2 and multiply the
number of heads by 2. This feature allows the BIOS to recognize a hard drive that
is larger than 504 MB.
LOGICAL BLOCKADDRESSINGLogical Block Addressing (LBA) linearly addresses sectors at Cylinder 0, Head 0,
and Sector 1 as LBA 0, then addresses everything, in sequence, to the last physical
cylinder of the disk (the standard SCSI addressing scheme). In LBA mode each
sector stores 512 Bytes of data.
Theoretically, LBA can address hard drive sizes as large as 128 GB. Without a
translated CHS, however, the BIOS will only recognize a drive as large as 8 GB,Chapter 10 Hard Disk Drives
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which translates to LBA limits of 1,024 cylinders, 256 heads, and 63 sectors per
track. The hard drive must be able to support LBA mode in order to be properly
configured.
DRIVE INTERFACE Hard disk drives can also be characterized by interface type.
On virtually all current computers, the drive interface will be onboard the
motherboard.
ENCODING SCHEMESHard disk drives can also be characterized by encoding method.
Encoding is the manner in which data is written to and read from the hard disk
drive. Various types of encoding methods have been used in hard disk drivesincluding Modified Frequency Modulation (MFM) and Run Length Limited
(RLL).
The data recorded onto the magnetic media is stored as 1s and 0s. Data placed on
the disk by the read/write heads is binary data in an encoded form. The drive
electronics has an Encoder/Decoder Chip (ENDEC) that takes the raw data and
converts it into magnetic pulses during the encode/write operation. During the
read/decode operation, it also converts the flux transitions or polarity reversals
picked up by the read head and converts them back into digital data.
When the digital data is applied to the read/write heads, the head creates a
magnetic field domain on the disk media with specific polarities. When a positive
current is applied to the write heads, the magnetic domains are polarized in one
direction. When a negative current is applied to the heads, the magnetic domains
are polarized in the opposite direction. As the write head is being pulsed, it is
writing data to the platters.As the head encounters a group of magnetic domains during the read operation, it
senses any changes in the magnetic domain polarity or flux reversals. Two
encoding methods are in use today.
FM ENCODING Although FM encoding is not used today, it did lead to the development of MFM.
With FM encoding, a flux reversal in each bit cell is recorded to indicate logic 1.
No flux reversal is indicated as logic 0. Each bit requires a transition cell. Logic 1
is recorded as a clock flux reversal followed by a data flux reversal. Logic zero is
seen as no clock reversal. Since there are two transition cells, the amount of data
the drive can hold is reduced.
MFM ENCODING Twice the amount of data is written in the same number of flux reversals and
clock speeds are doubled in MFM encoding. Floppy disk drives use MFMencoding. As explained earlier, early hard drives used FM encoding and were
limited in their capacity.
RLL ENCODING Run Length Limited (RLL) encoding is used on all hard drives today including
SCSI drives. RLL increases the drive capacity by over 50 percent. In RLL, groups
of bits are written or read as a unit, then combined to generate specific patterns of Chapter 10 Hard Disk Drives
10-26 Graymark DFnDR Trainer
reversal. Clock and data are combined in these patterns. RLL is defined from two
specifications of this code, which is the minimum number (run length) and the
maximum number (run limit) of transition cells allowed between two flux
transitions. The version of the RLL scheme is written as RLL2, 7. There can be as
few as two and as many as seven transition cells separating two flux transitions.SUMMARYAfter successfully completing this chapter, you have the knowledge to:
1. List hard disk drive specifications2. Describe the electro-mechanical components in a hard drive
3. Identify the different types of hard drive interfaces
4. Explain how a hard drive operates
5. Understand the purpose of a hard drive jumper
6. List the various encoding schemes used in hard drives
This completes Chapter 10. Proceed to the next chapter.