Managing Storage Technology

Understanding Hard Drive Terminology

If you took a martial arts class, the instructor would show you how to do some basic punches and kicks before letting you spar or compete. The instructor would be well aware that jumping into combat without the basics could do you more damage than good. PC repair works the same way: Before discussing the installation and configuration of IDE and SCSI devices, it is important to cover some basic terminology surrounding hard drives.

Hard drives are used to store data so that the data can be retrieved at a later time. A hard drive can be internal to the system using technologies such as IDE, SCSI, or SATA (you find out more about those technologies as the chapter progresses), or the drive can be an external drive connected via USB, FireWire, or eSATA.

You can also purchase network attached storage (NAS) today that connects to the network via an Ethernet connection. What is also exciting about today’s systems is that the drives are hot swappable, meaning that you can disconnect and connect the drive with the system running.

Disk geometry

The following sections introduce you to disk geometry — essentially the physical components of a drive that make up your data storage solution. You also find out some general terminology about hard drives and hard drive storage in this section.

Platters

A platter is a physical object (actually, a plate) inside the hard disk that is responsible for storing the data. A platter is similar to a music record (remember those old LPs your parents or grandparents had around the house?) in the sense that it spins on a spindle that runs through the center of the platter. A hard disk has many platters. Figure 5-1 shows the platters inside a hard disk.

FIGURE 5-1: The internals of a hard disk.

Not only are the platters similar to records on a record player in the sense that they spin on a spindle that runs through the center of all the platters, but they also store the data on tracks like tracks on a record. Each platter has two sides for storing information, and each side of the platter has a unique ID. The ID for the first side of the first platter is 0, and each side increases by 1. For example, two platters are in the disk, the first platter has side 0 and side 1, and the second platter has side 2 and side 3. Figure 5-2 illustrates this concept.

Because each side of the platter has a writing mechanism, many people use the terms “head” and “side” interchangeably. The head is more accurately called the read/write head because it moves over the disk surface and reads from or writes to the disk. Like a needle on a record player, the read/write head moves over the surface of the disk with the help of an arm, called the actuator arm or the head positioning mechanism. Figure 5-1 illustrates the read/write head on an actuator arm.

Each platter surface on the disk has its own read/write head. When information is written to the disk, the read/write head moves to the same track on all platters in a single movement and then writes the data across the same track on all platters. The actuator arm has multiple read/write heads on it.

Tracks

Just like there are grooves (tracks) on a music record, there are also tracks on each platter. These tracks are evenly spaced across the platter’s surface.

Sectors

The platter is divided into pie-shaped slices, called sectors. Now the confusing thing about sectors is that where a track intersects with a sector, sector blocks are created — also known as sectors! Each sector (block) — 512 bytes in size — is the actual storage area for data. Under the hood, the drive controller may not actually use 512 bytes, but use a larger value and emulate 512 bytes for backward compatibility.

Figure 5-3 illustrates the tracks and sectors on a disk platter. Each pie-sliced sector has an address; the first sector is sector 1, the second sector is sector 2, and so on. The reason why the term sector applies to two different areas of the disk is because if you were to look at a sector (the pie slice), like the pie slice labeled in Figure 5-3 as “Sector,” it might be sector 1. All sector blocks in that pie slice are considered sector 1 as well, but they differ in the track that they reside on.

FIGURE 5-3: Tracks and sectors on a disk platter.

So, each sector block has an address comprising the platter side number, the sector, and track number. For example, data can be saved to side 1, sector 2, track 4 — which is the address of a 512-byte sector block. Note that the term sector block is a term that I made up for this discussion; the term sector is also used to describe the 512-byte blocks.

Clusters

A group of sectors makes up a cluster, which is the allocation unit for a file — meaning where a file is saved. When a partition (a logical division of space on the disk; see Chapter 6 in this minibook for more on managing partitions and volumes) is formatted, the file system determines the cluster size based upon the partition size. For example, a 2GB FAT partition uses a 32K cluster size. That same 2GB partition formatted as FAT32 uses only a 4K cluster size.

Having a partition use a 4K cluster size means that eight sectors make up a cluster. Keep in mind that after a file is saved to the cluster, no other file can occupy that cluster. For example, if you have a 32K cluster size and you save a 3K file to the hard disk, the file is saved to an empty cluster — but only 3K of that cluster is used, and the remaining 29K is empty. The remaining 29K is now considered unusable space; no other file can be saved to that unused 29K.

Cylinders

All platters in the hard disk contain the same number of tracks, but that number varies from one hard disk to another. These tracks are numbered from the outside in, starting with 0 (zero). For example, on a platter with ten tracks, the track closest to the outer edge of the platter is track 0, and the track closest to the center is track 9.

A cylinder consists of the same track on both sides of all the platters. In other words, when you reference track 0, you reference a particular track on a particular platter; however, when you reference cylinder 0, you reference track 0 on all platters.

If you know the number of cylinders, heads, and sectors per track, you can calculate the size of a disk. For example, if a drive has 4,092 cylinders, 16 heads, and 63 sectors per track, the size of the disk is 2,111,864,832 bytes (2.1GB). The formula to calculate the size of the disk is

cylinders × number of heads × number of sectors per track × 512 bytes per sector

Read/write process

Platters are typically divided into 512-byte sectors. These sectors are the area on the platter that data is written to. The platters have a magnetic coating applied that is extremely sensitive to magnetism. While the platters spin, the read/write head moves from track to track until it reaches the desired track. Then it waits for the appropriate sector to move underneath it, at which time the read/write head is energized to apply a magnetic charge to the particles in the disk coating. This changes the particle binary state from 0 to 1, thus creating data. The same happens when the data needs to be read: The read/write head moves over the appropriate sector and reads the data that resides in the sector.

The read/write heads don’t actually touch the surface of the disk platters; instead, they hover about 10 micro-inches (or millionths of an inch) above it. (That’s not even enough space to place a hair between the read/write head and the platter’s surface.) This design helps improve disk performance because a read/write head that makes contact with the platter causes friction, slowing down the rotation speed of the disk and creating extra heat.

Performance

Magnetic disk performance can be measured in terms of several important characteristics:

Seek time is how long it takes to move the read/write heads to the desired track. Seek time is a calculated average because the time it takes to move to the desired track differs from one instance to another. For example, if the read/write heads are on track 1, they will take longer to move to track 12 than to track 3. Seek time is measured in milliseconds (ms), or one-thousandth of a second. Figure 5-4 shows how seek time is measured.
Latency is how long it takes for the appropriate sector to move under the read/write head. Latency is measured in milliseconds.
Access time describes the overall speed of the disk. It is a combination of seek time and latency. The lower the access time, the better.
Spin speed is how fast the platters spin, measured in rotations per minute (rpm). The larger the rpm value, the faster the disk, which means less latency.

I want to make a note about the spin speed of the drive. Today, the rpms are how we measure the speed of the drive. Common examples of rpms are 5,400 rpms, 7,200 rpms, 10,000 rpms, and finally 15,000 rpms. The more rotations per minute (rpm), the faster the drive is. For example, a 7200-rpm drive is faster than a 5400-rpm drive. A typical drive you install today in a workstation is 7200 rpm. You may want to install faster drives in servers.

Master Boot Record

The Master Boot Record (MBR) is the first sector on the first track of the first side of the first platter; it holds the operating system (OS) boot code that controls the loading of the OS.

The MBR also holds drive characteristics, such as the partition table. During the boot process, the system has to find a primary partition that is active — it does this by looking at the partition table in the MBR.

In general, if anything goes wrong with the MBR, you will not be able to boot the system. Because the boot record is always in the same location on every disk, it becomes very easy for a malicious hacker to write viruses that modify or corrupt the MBR. This is one reason you should always run virus-detection software. See Book 9, Chapter 3 for more on virus detection and protection.

Troubleshooting MBR disks

CompTIA wants you to know some common command-line tools for troubleshooting hard disks. Technically, these tips and tools apply to either MBR or GPT disks, but it makes sense to me to include them here. When troubleshooting a Windows 7 or Windows 8.1 system, you can gain access to these tools on a Windows 7 or Windows 8.1 system by restarting the computer into the Windows Recovery Environment (RE).

BOOTREC is a “Swiss Army Knife” utility that can repair all sorts of MBR problems. Specifically, remember the /FixMbr, /FixBoot, /ScanOS, and /RebuildBCD parameters for your A+ Exams.
CHKDSK is an ancient file system scanning and repair tool.
FORMAT is used to prepare a hard disk partition by laying down a file system and assigning a drive letter; at that point the partition becomes a volume.
DISKPART is the command-line equivalent to the Disk Management MMC console in Windows.
DEFRAG is the command-line variant to the Windows 7 Disk Defragmenter tool. Running this command periodically on magnetic disks will maximize disk I/O performance.
File recovery software varies in Windows, depending on the operating system version. Windows 8.1 includes the File History feature, which saves copies of your work periodically to another volume and can restore previous copies of content that you’ve changed or deleted.

Discovering IDE Devices

In the following sections, you find out how to install and troubleshoot IDE devices. First, you get an overview of IDE devices and some of their features, and then you see a number of different configurations for installing IDE devices into a computer system.

Before your operating system, be it Windows, OS X, or Linux, can work with any type of hard drive, you must initialize the disk by using the appropriate OS feature or tool. For example, use the Disk Management utility to initialize IDE, SATA, and/or USB disks. Having said that, let’s continue our detailed consideration of the historically relevant IDE hard disk drives.

IDE overview

The hard drive controller is responsible for converting signals made by the system CPU to signals that the hard disk can understand. These signals include instructions on where to find data and how to get to that data. The hard disk performs its task, and any data that needs to be returned is sent to the controller from the hard disk. The controller then converts the signals from the hard disk into signals that the system can understand.

In the past, the controller was on an expansion card, which was connected to the drives via ribbon cables. The goal of IDE was to make the installation of hard disks easier by including the controller on the hard disk, which is where the name comes from: Integrated Drive Electronics (IDE). So, today’s drives have the controllers integrated into the drives themselves, meaning the drive is its own boss.

Originally, IDE was available only in the flavor of hard drives; you did not have any other type of IDE device, such as CD-ROM or tape drives. IDE hard drives had a maximum capacity of about 528MB. Another important limitation with IDE is that only two devices could be connected in a chain. Back in the day when IDE was first used, SCSI was better in that respect because it supported eight devices in a chain. (Read more on SCSI in the later section, “Learning How SCSI Works.”)

Original IDE devices have a transfer rate of about 10 MBps and may have cache on the drive itself. Cache memory is a small amount of memory for storing data frequently used to increase drive performance.

Because of its limitations, IDE has been replaced by Enhanced Integrated Drive Electronics (EIDE). EIDE devices have a transfer rate of about 16 MBps. Four devices are allowed in an EIDE chain, with a greater variety available. For example, you may now add CD-ROMs and even Zip drives to an EIDE chain. Note that the capacity of the drives has been dramatically increased with EIDE — it now supports drives of over 200GB! Table 5-1 compares the features of IDE and EIDE.

TABLE 5-1 IDE versus EIDE

Characteristic	IDE	EIDE
Size	528MB	200GB and higher
Devices in chain	2	4
Transfer rate	10 MBps	16 MBps and higher
Types of devices	Hard drives	Hard drives, CD-ROMs

IDE has been around for quite some time now and has gone through some changes. The following sections outline some technologies and terms that describe the different versions of IDE. Be sure to know these for the A+ Exams.

IDE/ATA standard

A number of hard drive standards have been developed over the last two decades, the first major standard being the IDE standard. The IDE standard, which has been around since 1989, calls for an integrated controller on the drive to manage information entering and leaving the hard disk.

IDE drives attach to the motherboard by means of a 40-wire ribbon cable. The IDE standard also allows two drives to daisy chain, creating a master/slave relationship between devices. The master drive is responsible for sending and receiving information in the chain.

The IDE standard is also known as the Advanced Technology Attachment (ATA) standard, sometimes called the ATA-1 standard.

EIDE/ATA-2 standard

The EIDE standard followed shortly after the IDE standard. The EIDE standard allows four drives to be connected to a dual-channel controller. This is usually implemented as a motherboard with two connectors (also known as controllers) — one primary and one secondary. You could then connect two drives off of each controller, making a master/slave chain for each controller. EIDE also supports larger hard disks than the original IDE standard; the original size of an IDE drive was approximately 528MB. The EIDE standard is also known as ATA-2 standard.

Most techies in the computing industry interchange IDE and EIDE. For example, if you have a newer motherboard that uses EIDE drives, most documentation and technicians simply use the term IDE even though the drives might be EIDE, or even an Ultra DMA (direct memory access) drive. Also note that most techies and documentation use the term “controller” for the connectors on the motherboard that you connect the drives to, but really the controller is the circuitry on the hard drive that controls access to the drive. My point is get used to people using the term IDE instead of EIDE, and controller instead of connectors.

ATAPI specification

Originally, IDE devices were implemented as hard drives, but an additional ATA specification allows other types of devices to exist on an ATA (or IDE) chain. This specification is the ATA Packet Interface (ATAPI), which allows devices like CD-ROMs and tape drives to exist on an ATA chain. Other types of ATAPI devices are CD writers, DVD devices, and Zip drives.

Drive performance

The performance of the drive is determined by the Programmed I/O (PIO) mode or DMA mode it supports. The PIO mode or DMA mode is a protocol that determines the transfer rate of the drive. A number of different PIO modes and DMA modes are supported by devices, as shown in Table 5-2.

TABLE 5-2 PIO and DMA Modes

Mode	Runs At	Used By
PIO Mode 0	3.3 MBps	ATA-1
PIO Mode 1	5.2 MBps	ATA-1
PIO Mode 2	8.3 MBps	ATA-1
PIO Mode 3	11.1 MBps	ATA-1 and ATA-2
PIO Mode 4	16.6 MBps	ATA-1 and ATA-2
DMA 33	33.3 MBps	Ultra DMA drives
DMA 66	66 MBps	Ultra DMA drives
DMA 100	100 MBps	Ultra DMA drives
DMA 133	133 MBps	Ultra DMA drives

Be sure to know what a PIO mode is and also the transfer rates of Ultra DMA drives.

Installing IDE devices

In this section, I show you how to install an IDE device. Because all hard drives are different, I present only the most popular solutions for installing hard drives.

First, you want to open the casing of the computer and find an empty bay for mounting the new hard disk. If you are removing the old hard drive, you can use the same bay. If you are adding a hard drive, find an empty bay and mount the drive there. Second, you slide the drive in the bay so that the power connector and ribbon cable connector face the motherboard. Figure 5-5 shows an IDE drive being placed into the mounting bay.

FIGURE 5-5: Mounting the hard disk into the drive bay.

IDE cabling

After you mount the drive in place, the third step is to connect the IDE connector on the motherboard to the IDE connector on the hard disk with a 40-wire IDE ribbon cable. Then connect a power connector to the drive. Figure 5-6 shows an IDE ribbon cable.

One of the wires (wire 1) on the IDE ribbon cable is a different color than the others; usually, it’s red, but it might be blue. Wire 1 must be placed over pin 1 when connecting the ribbon cable to the hard drive and motherboard — the Pin 1 rule.

The big question is how to determine which pin is pin 1. Hopefully, the manufacturer indicates pin 1 by placing a small 1 near it. If you look at the connector on the hard drive and on the motherboard, you might see a small 1 on one end of the connector. That’s where you need to place wire 1 when connecting the ribbon cable.

Sometimes a manufacturer might not have enough space to indicate pin 1 and so does the opposite — indicate pin 40. This method gives you the same information, though: If you know what side pin 40 is on, you know that pin 1 is on the opposite side.

After you connect the IDE ribbon cable, connect the hard disk power from the power supply so that you can run the motor in the drive. (People often forget this step and then wonder why the drive doesn’t work.) Figure 5-7 shows how to connect the ribbon cable and the power supply cable to the hard disk.

Master/slave configuration

If you are installing multiple IDE devices, you are creating an IDE chain. The chain will be made up of one 40-wire IDE ribbon cable with two drives connected to it. Most IDE ribbon cables today have three IDE connectors on them: one that connects to the motherboard and one for each of the two drives that can be connected in a single chain.

After the two drives are connected, configure the drives into a master/slave configuration. Use this type of configuration because each drive has a built-in controller that makes it act like its own boss. (Have you ever tried to work in an environment with two bosses? Not good.) The purpose of designating a master is to specify the boss of that chain — the controller responsible for communicating with the processor.

When setting up a multidrive system, you have two drives, each with a controller that can potentially send signals to and receive from the processor. To save confusion, one of the drives is designated as the master, which receives all signals from the processor and sends back any data on behalf of both drives. The other drive is designated as the slave, which passes any information it wants to send to the processor up to the master. The master then forwards that information to the processor. Figure 5-8 illustrates a multidrive system.

FIGURE 5-8: One drive is configured as the master, and the other is configured as the slave.

To configure the master/slave relationship, you have to configure the jumper settings on the drives. The idea of the procedure is similar for all drives, but because the actual jumper setting might be different for each type of drive, the best thing to do is review the documentation for the drive.

Most hard drives today have the jumpers labeled as Master and Slave. Configuring these drives is usually pretty straightforward. You place the jumper on the master setting for the drive you want to be the master of the chain (meaning that this drive will communicate with the processor directly), and you place the jumper to the slave setting for the drive you want to configure as the slave. The slave drive receives instructions from the master. Figure 5-9 displays master and slave jumper settings.

FIGURE 5-9: Adjust the jumpers to set one drive as a master and the other as a slave.

After you have decided which drive will be the master and which drive will be the slave, you will need to adjust the jumper on each drive to set the appropriate setting. For the hard disk that will be master, you will move the jumper to the master setting and for the drive that will be the slave, you move the jumper to the slave setting. Also note that you will configure an IDE CD-ROM or DVD the same way — as either a master or slave device in the IDE chain.

Many times, configuring your drives in a master/slave setup might not be as easy as it looks. What do you do when you cannot see a specific master or slave jumper setting? Many manufacturers place documentation on the back of the drive telling you how to configure the drive for master and slave setups. Unfortunately, this was not the case on a drive I had to configure in the office one day. So I went to the manufacturer’s website and found out that this drive had a jumper labeled J20; the website documentation stated that if the drive was the only drive or was the master in a dual-drive configuration, the jumper (J20) should be set. If the drive was the slave in the dual-drive configuration, the jumper (J20) should be removed. Figure 5-10 shows the configuration for this example.

FIGURE 5-10: Looking at an additional jumper configuration for a dual-drive setup.

The moral of the story: If you can’t find the jumper settings on the drives themselves, check out the drives’ documentation or go to the manufacturers’ websites.

If you end up supporting older systems, you will most likely end up installing Serial ATA (SATA) drives. By contrast, IDE, which supports up to four devices instead of two, is considered an “ancient” disk technology at this point and is included in the book mainly for historical reference.

Old computer systems have two IDE connectors on the motherboard: the primary IDE connector and the secondary IDE connector. Each connector can have two devices configured in a master/slave relationship, for a total of four devices. Typically, the devices can be hard drives, CD-ROMs, or DVD devices. The steps are the same for configuring master and slave relationships for a hard disk, CD-ROM, and DVD because they are all considered IDE devices. Typically, you configure the CD-ROM or DVD as the slave, but you could also make it the master device on the second IDE connector.

After configuring the jumpers on the drive, power-on the system. The computer should recognize the additional drive and take you into the CMOS setup program. When you review the CMOS settings, you should notice the new drive. If you do not see the new drive, verify the master and slave settings, and maybe even switch the roles of the drives and try again.

Learning How SCSI Works

You won't find traditional SCSI or serial-attached SCSI (SAS) hard drives in consumer computers. Instead, you find SCSI technology almost exclusively on server hardware and stand-alone disk arrays.

SCSI overview

SCSI is an acronym for Small Computer System Interface. The important part of this term is small computer, meaning that SCSI has its own brain — the SCSI adapter — that handles the SCSI environment. This SCSI adapter (also known as a SCSI card or SCSI controller) is responsible for managing all SCSI devices and controlling the conversation on the SCSI chain.

SCSI technology has many advantages over IDE technology, such as

The types of devices supported: SCSI supports a multitude of devices, including hard drives, CD-ROMs, scanners, printers, and tape drives, to name just a few. This is a huge benefit because originally IDE typically supported only hard drives and CD-ROMs.
The number of devices supported in a single SCSI chain (also known as a SCSI bus): Original versions of SCSI supported as many as eight devices in the chain, but one of those devices is the SCSI card added to the computer to give you the capability to use SCSI.

IDE allows only two devices in the chain, and EIDE supports four devices. With SCSI, you are not only allowed to have more types of devices but also to have more of those devices!

Original SCSI supports as many as eight devices in the chain. However, if the A+ Exams ask how many devices can be attached to a SCSI adapter, the answer is seven. If the test asks how many devices can exist in the SCSI chain, the answer is eight because the card counts as one of those devices. Remember to watch the wording of the questions closely.
The performance of SCSI over IDE devices: Original SCSI devices don’t compare in the performance category with EIDE devices, but some of the later SCSI technologies, such as SCSI-2 and SCSI-3, can outperform IDE and EIDE.

I give details about transfer rates of the different types of SCSI devices in the “Types of SCSI” section, later in this chapter.

For the remainder of this chapter, assume that you are dealing with original SCSI, also known as SCSI-1. In the “Types of SCSI” section, I discuss the newer types of SCSI.

Host adapter

When you install SCSI devices, you first need to install the SCSI host adapter, which is an expansion card that you add to the computer so you can chain SCSI devices off the adapter. In essence, the SCSI host adapter is the brain of the SCSI bus; it acts as the controller for the SCSI bus. Figure 5-11 shows a SCSI adapter being inserted into an expansion slot in the system.

The SCSI controller (adapter) is responsible for sending and receiving all information to and from the SCSI bus, just like the IDE controller. When the system has information for one of the devices in the SCSI bus, the system hands the information over to the SCSI controller, which then passes the information to the appropriate device in the chain. Figure 5-12 shows a SCSI bus — made up of the SCSI host adapter (the SCSI controller) — along with two internal SCSI devices and two external SCSI devices.

FIGURE 5-12: Looking at a SCSI daisy chain.

The beauty of the entire setup is that the SCSI adapter in the computer is assigned resources, such as an IRQ and an I/O address. Each device in the SCSI chain is not assigned these resources because all processor information passes to the SCSI controller, and the controller passes the information to the devices. This means that the system never talks to the devices directly, so each device does not require an IRQ and an I/O address.

When you purchase a SCSI adapter, first look inside your system to figure out what type of expansion slots are free. You will typically have some PCI slots, but you might have an ISA or EISA slot as well. The difference between these expansion slots is performance — PCI runs at 33 MHz, and ISA and EISA run at only 8 MHz. Also, PCI and EISA are 32-bit technologies, and ISA is only 16-bit. The bottom line is that if you have free PCI slots, you will probably end up purchasing a PCI SCSI adapter.

So the next big question is when the SCSI controller receives information for a particular device in the chain, how does it send the information to that device?

Addressing

Each device is assigned an internal address — a SCSI ID — in the SCSI bus. The SCSI controller knows the address of each device. When the SCSI controller receives information for a particular device, the controller references that device by its ID in the SCSI bus. This way, there’s no confusion as to whom the data is destined for.

You are responsible for assigning the SCSI IDs when you connect each device to the SCSI chain. You assign an ID either by jumpers or DIP (dual inline package) switches if the device is an internal device, or by a spinner if the device is external. A spinner is an indicator on the back of the external SCSI device whose value you can change by pressing the button to increase or decrease the SCSI ID. Figure 5-13 shows the back of an external SCSI tape drive and how to change the SCSI ID using the spinner.

FIGURE 5-13: Assigning a SCSI ID to an external device.

In Figure 5-13, you can also see the type of connector used for external SCSI devices. This is a Centronics 50-pin connector.

If you are installing an internal SCSI device, you will most likely need to assign the SCSI ID by using jumpers. Internal SCSI devices have a jumper set with three pairs of jumper pins. The numeric values associated with these jumpers, although probably not shown on the drive, are 4, 2, and 1 (from left to right). Table 5-3 shows this jumper setup.

TABLE 5-3 Jumper Block Settings

	J2	J1	J0
Numeric Value	4	2	1
SCSI ID 0	0	0	0
SCSI ID 3	0	1	1
SCSI ID 6	1	1	0

To assign the device a SCSI ID of 0, you would not add a jumper to any of the pins. This is shown in Table 5-3 by having the off state (represented by 0) at each jumper location. Another example of setting a jumper ID is assigning the device a SCSI ID of 3: Jumper the J0 pins and the J1 pins, but not the J2 pins. This enables decimal values of 1 + 2. Table 5-3 also shows what would happen if you want to set the SCSI ID to 6: Enable jumpers J1 and J2, which enables the decimal values of 2 + 4, while the jumper J0 has an off state.

The IDs you assign to each device are completely up to you, but note that the higher the number, the more important the device is to the SCSI bus. For example, if two devices need to send information through the bus at the same time, the device with the higher SCSI ID is always given priority. This is why the SCSI host adapter is usually assigned the highest number in the chain (usually 7 if the bus supports eight devices — the ID numbers start with 0).

So the host adapter is assigned an ID of 7, and a SCSI bootable hard drive is assigned a SCSI ID of 0, which is the SCSI ID that the controller automatically looks to in order to boot off a SCSI hard drive. Outside of that, you decide what the ID numbers are for each device. As a rule, give slower devices higher ID numbers so that they receive a higher priority in the SCSI bus. Devices with higher priority get access to the bus before lower priority devices.

SCSI cabling

Different types of cabling are used to chain SCSI devices to the SCSI adapter. Internal devices use a 50-wire ribbon cable; external devices require a thick Centronics cable to connect to the Centronics 50 (typically used by SCSI-1) or the Centronics 68 (typically used by wide SCSI-2 technologies or Ultra SCSI-3) connector on the back of the device.

The different versions of SCSI use a large number of different cable types. Figure 5-14 shows some internal SCSI connectors, and Figure 5-15 displays a handful of external SCSI connectors. Be sure to be familiar with these cable types for the A+ Exams.

FIGURE 5-14: Looking at internal SCSI connectors.

FIGURE 5-15: Looking at external SCSI connectors.

Termination

Both ends of the SCSI bus must be terminated so that when a signal is sent down the SCSI bus, it is absorbed at the end of the bus by the terminator. If the signal was not absorbed, or removed from the bus with a terminator, the signal would bounce back and collide with other data on the bus. A collision would destroy the signal. The first device in the chain must be terminated along with the last device in the chain, the first device usually being the host adapter. If the device is an internal device, terminating might involve modifying jumper settings. If the device is external, a terminator will be added to the back of the device. Figure 5-16 shows a terminator for external devices.

If your SCSI chain has a combination of internal and external SCSI devices, the card shouldn’t be terminated because it is no longer the end of the SCSI chain. Instead, you should terminate the devices at either end of the SCSI chain.

Most SCSI cards today are self-terminating, so you typically will not need to terminate them manually.

Types of SCSI

Over the past several years, SCSI technology has increased in performance to stay competitive with advances in IDE and EIDE. Newer versions of SCSI have amazing transfer rates, which is one of the reasons why you find network servers using SCSI hard drives instead of EIDE devices. The following list outlines the key points about the different versions of SCSI:

SCSI-1: The original version of SCSI (SCSI-1) was an 8-bit technology with a transfer rate of 5 MBps. One of the major benefits of SCSI was that you were not limited to two devices in a chain like you are with IDE. SCSI-1 allowed you to have eight devices in the chain, with the controller counting as one.
Fast SCSI-2: Fast SCSI-2 increased the performance of SCSI by doubling the transfer rate. Fast SCSI-2 devices transfer information at 10 MBps. Fast SCSI-2 is still an 8-bit technology and supports eight devices in the chain.
Wide SCSI-2: Wide SCSI-2 doubled the 8-bit data path of SCSI to 16 bits. Doubling the width of the data path raised the transfer rate to 10 MBps, like Fast SCSI-2, but Wide SCSI-2 can support 16 devices in a chain.

When trying to remember the difference between SCSI-1, Fast SCSI-2, and Wide SCSI-2, think of it this way. Fast implies speed, so the transfer rate is increased. Wide implies “wider” or bigger, which is the data path that has been increased; as a result, you also get a higher transfer rate.
Fast Wide SCSI-2: Fast Wide SCSI-2 is the combination of Fast SCSI-2 and Wide SCSI-2. The data path of Fast Wide SCSI-2 is 16 bits, the transfer rate is 20 MBps, and it supports 16 devices in a chain.
Ultra SCSI: Ultra SCSI takes the transfer rate of 10 MBps and doubles it again to 20 MBps! With Ultra SCSI, the bus width is only eight bits, and the number of devices that exist in the chain is eight.
Ultra Wide SCSI: Ultra Wide SCSI is Ultra SCSI with the bus width increased to 16 bits, and the number of devices in the chain is increased to 16. The transfer rate of Ultra Wide SCSI increased to 40 MBps.
LVD (Ultra2 SCSI): Low Voltage Differential (LVD), also known as Ultra2 SCSI, has a bus width of 16 bits and supports up to 16 devices. LVD is a popular SCSI version due to having a high transfer rate of 80 MBps. Figure 5-17 shows an LVD adapter (or card) with a cable and hard drive.

FIGURE 5-17: An LVD SCSI card with hard drive and internal cable.

Be prepared to answer questions on the A+ Exams about the different types of SCSI. I suggest memorizing the transfer rates of each type.

Installing SCSI devices

If you understand the issues with SCSI, installing a SCSI bus is fairly simple. First, assign a unique ID number to each device. I usually perform this step at the beginning so that when everything is connected, I won’t have to play around figuring out how to change the ID of the devices. For more on assigning the IDs, see the section, “Addressing,” earlier in this chapter.

When assigning the ID numbers, remember that you want to assign the bootable drive the ID of 0 because the SCSI host adapter automatically looks to SCSI ID 0 for a bootable device. You also want to enable the SCSI BIOS on the SCSI controller if you are booting off a SCSI hard disk. When you enable the SCSI BIOS, you won’t need to install a driver for the card because the PC will recognize the device on startup. If you are booting off an IDE drive and using the SCSI disk as an additional drive, disable the SCSI BIOS and install a driver in the OS.

After you assign the ID numbers to each device, insert the SCSI host adapter into the expansion slot of the PC. After inserting the SCSI card, chain all devices.

When preparing for the A+ Exams, know the different terms used for a particular technology. Another term for a SCSI chain is a daisy chain. When you chain devices, you create a daisy chain.

When you have the devices chained, make sure that each end on the SCSI bus is terminated. If the last device is an external device, put the terminator on the end of the device. If you are installing internal devices, check the documentation on the internal devices to find out what jumpers to set.

At this point, the IDs are configured for each device, the SCSI card is inserted into the PC, and the devices are connected to the card to create a SCSI bus. The SCSI bus is also terminated at either end. Before installing the driver for the SCSI card in the operating system, review the steps to install a SCSI device one last time. To install a SCSI bus, follow these steps:

Assign unique IDs to each device.
Install the SCSI host adapter into the expansion slots.
Chain devices to the SCSI host adapter.
Terminate the SCSI bus at both ends of the chain.
Install the driver for the SCSI card if you are not booting off the first hard disk.

After you connect the hardware for the SCSI chain, you need to load a driver in the OS for the SCSI host adapter. After inserting the SCSI card and powering-on the Windows OS, Plug and Play should kick in, asking for the driver of the new hardware. If Plug and Play does not kick in, you can run the Add Hardware Wizard found in the Control Panel or My Computer properties of the system. To install a SCSI adapter in Windows if it is not detected automatically, follow these steps:

In Windows XP or Server 2003: Right-click My Computer and choose Properties. Then go to the Hardware tab and click the Add Hardware Wizard button.
Click Next.
Select Add or Troubleshoot a Device and then click Next.
In the Choose Hardware Device dialog box, select Add a New Device and then click Next.
Choose the adapter to install, so select No, I Want to Select the Hardware from a List. Click Next.
- If you know the host adapter you are installing: Select No, I Want to Select the Hardware from List.
- If you are unsure of the host adapter you are installing: Select Yes, Search for New Hardware.
The next screen asks you what type of device you are installing.
Choose SCSI and RAID controllers and then click Next.
In the list of devices, select the manufacturer on the left side and the adapter to install on the right side; then click Next.
Click Finish.
Restart the computer.

The steps to install a driver manually in Windows 7 and Vista are similar to Windows XP. To launch the Add Hardware Wizard in Windows 7 and Vista, if Plug and Play has not loaded your device driver, you simply choose Start ⇒ Control Panel ⇒ Hardware and Sound ⇒ Device Manager (found under the Devices and Printers category). Once in the device manager, right-click on your computer at the top of the screen and choose Add Legacy Hardware — the Add Hardware Wizard will launch.

Understanding Serial ATA

IDE technology has been around for many, many years, and there has been a big need for a change in hard drive technology. That change came as a new hard drive interface called serial ATA (SATA). IDE is a parallel technology (PATA), and although SATA is a serial technology, it offers great speed and other benefits. SATA is also a lot faster than IDE — approximately 30 times faster, with original speeds of 150 MBps and speeds of 2,000 MBps for SATA 3.2.

One of the first benefits of SATA is that it is a hot-swappable technology, meaning that you can add or remove drives from the system without shutting down the system. This is a huge benefit when you look for RAID solutions for servers that you don’t want to spend a lot of money on — like a server for a small company. (For more on RAID, see the section “A Quick Tour of RAID,” later in this chapter.)

Another benefit of SATA is in the cabling. Because SATA is a serial technology, the cables can be longer than your typical IDE ribbon cables. I don’t know how many times with IDE I had to switch the CD-ROM and my second hard drive around just so the ribbon cable could reach. SATA cables can be 39 inches long, but the maximum distance for IDE is 18 inches.

The other benefit of the cabling with SATA is that it uses only 7 wires, as opposed to the 80 wires used in newer IDE drives. The benefit here is that it allows for better airflow in the system, which results in a cooler system. Figure 5-18 shows a SATA drive and cable.

FIGURE 5-18: A SATA cable and power connector connecting to a SATA drive.

With IDE, you have to master and slave the drives when you want multiple IDE devices. Yet another benefit to SATA is that there is no mastering and slaving of devices because you can only connect one SATA device to a single connector, or channel. The reason this is a benefit is because when installing a drive, you don’t need to have knowledge of mastering and slaving devices — you simply connect the SATA device to the system!

SATA has all but replaced drive technologies like EIDE and SCSI, and currently has three versions:

SATA v1: 150 MBps transfer rate
SATA v2: 300 MBps transfer rate
SATA v3: 600 MBps transfer rate

If you want two SATA drives, you need two SATA connectors — and don’t forget that you can get cards to give you more connectors, allowing you to install additional SATA devices.

One last note on SATA: Your BIOS offers a SATA operation mode setting that you may want to check. If you want the controller to support old PATA drives, you can set the operation mode to parallel mode (also known as compatibility mode). If you are using SATA in the system, set the operation mode to AHCI to leverage the benefits of SATA; this also supports the SATA drives in a RAID configuration. Most systems also have a RAID mode if you know you are configuring the SATA systems in a RAID configuration (use AHCI if you are not sure).

Lab 5-1 demonstrates how to install a SATA drive. Lab 5-1 can be found on the companion website at www.dummies.com/go/aplusaio.

eSATA drives

eSATA — external SATA — allows for external hard drives to connect to a system over a SATA port instead of the typical USB or FireWire port. In the past, external drives were enclosures that held SATA drives, but the interface to connect the enclosure to the computer used USB or FireWire. This created overhead as the SATA interface is translated to USB or FireWire, which is slower than SATA. With eSATA connections on the motherboard, you can connect to the external drive using eSATA, thus leveraging SATA speeds with no translation drawbacks!

You should always have at least one USB external hard drive enclosure (along with screwdrivers) in your troubleshooting toolkit. I cannot count how many times I’ve used them to restore files from a customer’s old computer to a new one.

An eSATA device requires its own power source (it is an external device) and can have an external SATA cable length of 2 meters. eSATA cable is specially designed to help prevent electromagnetic interference (EMI). eSATA cable has also been designed to handle more than 5,000 times of adding and removing of the drive; the current internal SATA cable is suited for only 50 insertions and removals. Figure 5-19 shows an eSATA connector on a 1TB (terabyte) external hard drive.

FIGURE 5-19: An eSATA connector on an external hard drive.

Using Removable Storage

Not all data storage is hard-wired to the system. Removable storage is the term used for storage media that you take away from the system with you.

CD-ROM/CD-RW

A compact disc–read-only memory (CD-ROM) is an optical storage technology that uses a laser to read and write data. Originally, as the name implies, one could only read from CD-ROMs. CD-ROMs have essentially gone the way of the dodo; DVD media is by far the standard nowadays.

Originally, CD-ROMs stored 650MB of data and could store 74 minutes of music, but today’s CD-ROMs store 700MB of data or 80 minutes of music. CD-ROMs are written to from the inside out. If you look at the bottom of the CD-ROM, you see the lines indicating where data was written, which is very useful information if you ever pick up a CD and wonder whether it has been written to.

The speed (transfer rate) of the CD-ROM, measured in multiples of 150 KBps, is indicated with an X. For example, an old 1X (pronounced “one times”) CD-ROM had a transfer rate of 150 KBps, and an 8X has a transfer rate of 1200 KBps (150 × 8 = 1200), and a much faster 48X has a transfer rate of 7200 KBps.

For many years now, CD drives are writeable: If you want to burn your own CD you can if you have a CD burner. (Writing to a CD is often called burning a CD.) This makes CD drives much more popular than the older floppy drives because of the amount of information you can store on the CD — a great solution for backing up your data!

The two types of writeable CDs are CD Recordable (CDR) and CD ReWritable (CD-RW). The difference between them is that you can write to CDR only once, but you can reuse a CD-RW many times by reformatting the CD and starting again.

CDR speeds are shown in a format like 4 x 24: The first value is the record speed, and the second value is the read speed. Each value is multiplied by the 150 KBps to calculate the record and read speed. CD-RW displays three values to indicate the speed of the device: write speed, rewrite speed, and read speed — for example, 4 x 4 x 24.

A CDR is an example of a write once read many (WORM) disc. Remember for the A+ Exams that the CDR speed is displayed with the record speed showing first and then the read speed (4 x 24). CD-RW displays the speed as the write speed, rewrite speed, and read speed (4 x 4 x 24).

You can write to a CDR multiple times, but you cannot overwrite areas of the disc that have already been written to. With a CDR, writing to it many times appends the additional write operations information to the end of the CDR. Each burn operation that you perform is a session, and most writeable CD drives today support multiple sessions. For example, say you back up your pictures to CD and use only 350MB of space on the CDR. You can write more data to the CD with the remaining space at a later time. With the cost of CDRs being so low nowadays, I typically don’t bother. I burn a CD, label it, and then file it.

When writing to a CD, the process is not done magnetically like it is with hard drives. As I mention earlier, the write operation is performed with a laser. The CD has a chemical-dye layer mixed with a thin reflective layer. When you write to the CD, the chemical layer is heated with the laser to create a solid state at that location. These locations reflect less light, and the different patterns of reflection create the data on the disk.

Many CD burners (used to write to CDs) come as combo drives that can burn CDs and read DVDs. The key point to remember about these combo drives is they cannot write to DVDs.

DVD/DVD-RW

Digital versatile discs (DVDs) are similar to CDs in the sense that they are another type of optical storage, but DVDs store a lot more data. The typical DVD stores 4.7GB of data. Some DVDs (unlike CDs) can store data on both sides of the disc, and newer DVDs even store data on different layers on the DVD. This allows the DVD to store more than the 4.7GB, depending upon the DVD standard. Table 5-4 describes the different DVD standards.

TABLE 5-4 DVD Standards

Standard	Specifications	Total Storage Space
DVD-5	Single-sided, single layer	4.7GB
DVD-9	Single-sided, double layer	8.5GB
DVD-10	Double-sided, single layer	9.4GB
DVD-18	Double-sided, double layer	17GB

The transfer rates of DVDs are measured in a similar fashion to CD-ROMs but the transfer rate is 1.35 MBps for each times (X). For example, if you have a 2X DVD-ROM, it has a transfer rate of 2.70 MBps. An 8X DVD-ROM has a transfer rate of 10.80 MBps.

Double layer, also called dual-layer, discs store more data than single layer optical storage because you can write two separate data streams to the disc. Technically, these data streams are dye layers; you can see the color difference when you inspect the bottom of a “burned” DVD-DL disc.

Blu-ray discs

Blu-ray discs are popular items today in the video world because they offer the capabilities of high-definition (HD) video. Blu-ray has much better quality than DVD.

Blu-ray, created by Sony, was named after the fact that a blue laser is used to read and write to the Blu-ray disc. (DVDs use a red laser.) Not only does Blu-ray offer HD video, but it also stores more information than a DVD. Blu-ray discs can store up to 25GB of data for a single-layer disc, but can store up to 50GB of data for a double-layer disc!

Blu-ray discs also have a faster transfer rate than DVDs. DVD speeds could be calculated by taking the speed indicated and multiplying it by 1.35 MBps, but a Blu-ray disc has a multiplier of 4.5 MBps!

BD-R and BD-RE

Blu-ray discs are like DVDs in that they have recordable versions as well. Blu-ray disc recordables (BD-Rs) are Blu-ray discs that can be written to once, while Blu-ray disc recordable erasables (BD-REs) can be erased and then written to many times.

Solid state drives

Solid state drives (SSDs) use a totally different approach to storing data on the drive than conventional drives, which use magnetic states to store the data. Solid state drives do not have any moving parts such as platters or read/write heads; they simply store data permanently to a huge block of memory. Solid state drives outperform magnetic drives but are still costly, so you will see magnetic drives on lower-end PCs. On mid-tier computers and higher, you'll find SSDs are pretty standard.

Flash drives/thumb drives

Flash drives, also known as thumb drives or memory sticks, are the popular method for carrying data from computer to computer. Flash drives, which can store anywhere from 64MB to multiple gigabytes of information, are relatively inexpensive.

Flash drives are USB devices that you simply plug into the USB port on the computer. Plug and Play kicks in, detects the device, and assigns the drive a letter in the My Computer icon. To access the flash drive, you simply double-click the drive in My Computer and open, copy, and move files as you wish. Figure 5-20 shows a flash drive.

FIGURE 5-20: A flash drive uses a USB connection to interface with the computer.

Hybrid drives

A hybrid drive (also called an SSHD drive) is a traditional mechanical hard disk drive that includes on-board flash storage for use as cache. Thus, drive performance is improved because the disk controller has high-speed access to the SSD data cache.

SD cards

Multimedia devices, such as MP3 players and digital cameras, support adding memory to the device by using CompactFlash cards or Secure Digital (SD) cards (as shown in Figure 5-21).

FIGURE 5-21: A CompactFlash, SD card, and SD card carry case.

Related to the SD card standard is the embedded MultiMediaCard (eMMC). These tiny packages incorporate flash memory plus a controller and are typically installed permanently as a non-volatile memory system for mobile phones and tablets.

CompactFlash (CF) cards have been very popular but have been replaced by SD cards. SD cards are used by a number of types of devices such as digital cameras, laptops, printers, MP3 players, and PDAs to name a few types of devices. SD cards are a great way to carry your data from one device to another.

SD cards store data up to 4GB, but a newer SD format — Secure Digital High Capacity (SDHC) — can store information up to 32GB or even 2TB (!). The problem is that SDHC cards cannot be read by devices that only support SD cards. For a device to be able to read an SDHC card, the device must be compatible with SDHC. This is important to remember when you purchase an SD card for your camera. The SD and SDHC cards are the same physical size and appear the same; look for the label indicating SDHC on the SDHC card.

You should be familiar with a number of other types of removable media for the A+ Certification:

SDXC: The secure digital extended capacity (SDXC) cards allow up to 2 TB of space for the SD card.
Mini-SD: Mini-SD cards are smaller than the SD and SDHC cards, with dimensions of 21.5 mm × 20 mm × 1.4 mm.
Micro-SD: Micro-SD is the smallest type of non-volatile memory you can find today. Micro-SD memory cards are commonly used with mobile devices such as phones and tablets. You can also purchase an adapter that allows you to connect the micro-SD in a regular SD slot so that it can be used with a PC.
xD: Extreme Digital (xD) cards are older memory cards used in cameras that ranged in sizes from 16 MB to 2 GB. xD competed with other technologies such as CompactFlash and is no longer being used in newer cameras.

External hard drives

External drives are just as popular as flash drives today. Like flash drives, an external drive uses a USB connection, but could also allow you to connect the drive through FireWire or eSATA. External drives allow you to store hundreds of gigabytes, even a terabyte, of data. These are great solutions to add more space to a laptop computer or desktop PC.

Tape

A popular type of media for data is tape, which is typically used to store backup copies of data. This copy of the data stored on tape is used to bring the data back if the hard drive fails. Different types of tape drives are popular today:

Quarter-inch cartridge (QIC): QIC — one of the oldest and most popular tape standards — supports many different tape sizes. The QIC size depends on the standard, and each standard is labeled similar to QIC-80 — the QIC tape that supports 80MB of data. Other examples are QIC-40 (40MB tapes) and QIC-5210 (25GB tapes).
Travan: Travan is a tape drive standard based on the QIC standard but supports compression. Travan is typically more expensive and can store from 400MB to 8GB of data or more. Examples of tape sizes in this standard are labeled as TR-1 (stores 400MB of data) and TR-4 (stores 8GB of data).
Digital Audio Tape (DAT): DAT drives store data in a digital format and use two heads: one for reading data and the other for writing data. DAT drives use a standard called Digital Data Storage (DDS) to store data. Examples of DDS tapes are DDS-1 (stores 2GB of data), DDS-2 (stores 8GB of data), and DDS-4 (stores 40GB of data).

1. What is the size of a sector on a hard disk?

(A) 512 bytes

(B) 1K

(C) 4K

(D) 512K

2. How many devices can exist in an IDE chain?

(A) 1

(B) 2

(C) 3

(D) 4

3. What physical component of the disk is responsible for reading and writing data on the disk?

(A) Platter

(B) Sector

(C) Cluster

(D) Read/write head

4. What does DL mean in the acronym DVD-RW DL?

(A) Device Layer

(B) Dual Layer

(C) Disc Level

(D) Drive Letter

5. In a SCSI chain, what devices are required to be terminated?

(A) The first device in the chain

(B) The last device in the chain

(C) Devices at either end of the SCSI chain

(D) Any hard disk in the SCSI chain

6. In a SCSI chain, what device should take a SCSI ID of 0?

(A) CD-ROM

(B) The bootable (first) hard disk

(C) The SCSI host adapter

(D) Printer

7. Which of the following is considered a hybrid RAID type?

(A) RAID 0

(B) RAID 1

(C) RAID 5

(D) RAID 10

8. Which of the following describes the cabling for internal SCSI?

(A) 40-wire ribbon cable

(B) 34-wire ribbon cable

(C) 50-wire ribbon cable

(D) None of the above

9. Which of the following best describes where the Master Boot Record is located?

(A) Last track on the disk

(B) First track on the disk

(C) First sector on the first track of the first side of the first platter

(D) First sector on the last side of the last platter