The Harddisk Guide The hard disk can have a huge impact on the performance of your PC: The fact is that the rotating magnetic media of the hard disk is one of the severest performance bottlenecks, causing second-long delays while fat programs spin off the disk and into RAM. Whereas disk access times are measured in milliseconds, system RAM performance is counted in nanoseconds. Understanding hard disk operation - and optimizing - can eliminate teeth-grinding delays. The factors that affect the speed of a Hard disk: Rotation speed Number of sectors per track Seek time / head switch time / cylinder switch time Rotational latency Data access time Cache on the HD How data is organized on the disks Transfer rates Interface (EIDE / SCSI) What are sectors, tracks, heads and cylinders? On a Hard disk, data is stored in the magnetic coating of the disk. The so called head, held by an actor arm, is used to write and read data. This disk rotates with a constant turn time, measured in revolutions per minute (rpm). Data is organized on a disk in cylinders, tracks and sectors. Cylinders are concentric tracks on the surface of the disk. A track is divided into sectors. A Hard disk has a head on each side of a disk. Nowadays, the actuator arm is moved by a servo-motor (not a step-motor which needs more time while swinging in after moving over the desired track). All harddisks have reserved sectors, which are used automatically by the drive logic if there is a defect in the media. Rotation speed Typical harddisks have a rotation speed from 4,500 to 7,200 rpm, a 10,000 rpm drive just hit the market. The faster the rotation, the higher the transfer rate, but also the louder and hotter the HD. You may need to cool a 7200 rpm disk with an extra fan, or its life would be much shorter. Modern HD’s read all sectors of a track in one turn (Interleave 1:1). The rotation speed is constant. Number of sectors per track Modern harddisks use different track sizes. The outer parts of a disk have more space for sectors than the inner parts. Usually, HD’s begin to write from the outside to the inside of a disk. Hence, data written or read at the beginning of a HD is accessed and transferred faster rate. Seek time / head switch time / cylinder switch time The fastest seek time occurs when moving from one track directly to the next. The slowest seek time is the so called full-stroke between the outer and inner tracks. Some harddisks (especially SCSI drives) don't execute the seek command correctly. These drives position the head somewhere close to the desired track or leave the head where it was. The seek time everyone is interested in is the average seek time, defined as the time it takes to position the drive's heads for a randomly located request. Yes, you are correct: seek time should be smaller if the disk is smaller (5 1/4", 3 1/2" etc.). All heads of a Hard disk are carried on one actuator arm, so all heads are on the same cylinder. Head switch time measures the average time the drive takes to switch between two of the heads when reading or writing data. Cylinder switch time is the average time it takes to move the heads to the next track when reading or writing data. All these times are measured in milliseconds (ms). Rotational latency After the head is positioned over the desired track, it has to wait for the right sector. This time is called rotational latency and is measured in ms. The faster the drives spins, the shorter the rotational latency time. The average time is the time the disk needs to turn half way around, usually about 4ms (7200rpm) to 6ms (5400rpm). Data access time Data access time is the combination of seek time, head switch time and rotational latency and is measured in ms. As you now know, the seek time only tells you about how fast the head is positioned over a wanted cylinder. Until data is read or written you will have to add the head switch time for finding the track and also the rotational latency time for finding the wanted sector. Cache I guess you already know about cache. All modern HD’s have their own cache varying in size and organization. The cache is normally used for writing and reading. On SCSI HD’s you may have to enable write caching, because often it is disabled by default. This varies from drive to drive. You will have to check the cache status with a program like ASPIID from Seagate. You may be surprised that it is not the cache size that is important, but the organization of the cache itself (write / read cache or look ahead cache). With most EIDE drives, the PC’s system memory is also used for storing the HD’s firmware (e.g. software or "BIOS"). When the drive powers up, it reads the firmware from special sectors. By doing this, manufacturers save money by eliminating the need for ROM chips, but also give you the ability to easily update your drives "BIOS" if it is necessary (Like for the WD drives which had problems with some motherboard BIOS' resulting in head crashes!). Organization of the data on the disks You now know, a Hard disk has cylinders, heads and sectors. If you look in your BIOS you will find these 3 values listed for each Hard disk in your computer. You learned that a Hard disk don’t have a fixed sector size as they had in earlier days. Today, these values are only used for compatibility with DOS, as they have nothing to do with the physical geometry of the drive. The Hard disk calculates these values into a logical block address (LBA) and then this LBA value is converted into the real cylinder, head and sector values. Modern BIOS’ are able to use LBA, so limitations like the 504 MB barrier are now gone. Cylinder, heads and sectors are still used in DOS environments. SCSI drives have always used LBA to access data on the Hard disk. Modern operating systems access data via LBA directly without using the BIOS. Transfer rates In the pictures you can see the several ways how data can be stored physically on the Hard disk. With a benchmark program that calculates the transfer rate or seek time of the whole Hard disk you can see if your drive is using a 'vertical' or a 'horizontal' mapping. Depending on what kind of read/write heads and servo-motors (for positioning the actuator arm) are used it is faster to switch heads or to change tracks.   The Interface (EIDE / SCSI) Currently there are 2 different common interfaces: EIDE and SCSI. You will find an EIDE controllers integrated with the motherboard and that EIDE harddisks are much cheaper than SCSI drives. For SCSI you need an extra controller, because there aren't a lot of motherboards with integrated SCSI controllers. Together with the higher price of a SCSI disk a SCSI system is more expensive than EIDE. The EIDE interface has a primary and a secondary channel that will connect to two devices each, for a total of four. That could be a Hard disk, CD-ROM or disk changers. Lately there have been tape backups with EIDE connectors, but you need special backup software. Scanners for example aren't available with EIDE interface, only with SCSI. You can connect up to 7 devices to a SCSI bus or 15 devices to a Wide SCSI. In a standard environment, the performance of single Hard disk won’t improve much from the SCSI interface. Rather, the power of SCSI is that several devices can use the bus at the same time, not using the bus while they don’t need it. So, we see the best benefit from SCSI when several devices are all used on the same bus. On one EIDE channel, the 2 devices have to take turns controlling the bus. If there is a Hard disk and a CD-ROM on the same channel, the Hard disk has to wait until a request to the CD-ROM has finished. Because CD-ROM's are relatively slow, there is a degradation of performance. That's why everybody tells you to connect the CD-ROM to the secondary channel and your Hard disk to the primary. The primary and secondary channels work more or less independently of one another (it's a matter of the EIDE controller chip). The SCSI interface comes in several types. 8-bit (50 wire data cable) or 16-bit (68 wire data cable, Wide SCSI). The clock can be 5 MHz (SCSI 1), 10 MHz (Fast SCSI), 20 MHz (Fast-20 or Ultra SCSI) or 40 MHz (Ultra-2 SCSI).   Possible transfer rates of the SCSI bus SCSIbus clock 8-bit (50 wire data cable) 16-bit (68 wire data cable, Wide SCSI) 5 MHz (SCSI 1) 5 Mbytes/s NA 10 MHz (Fast SCSI, SCSI II) 10 Mbytes/s 20 Mbytes/s 20 MHz (Fast-20, Ultra SCSI) 20 Mbytes/s 40 Mbytes/s 40 MHz (Fast-40, Ultra-2 SCSI) 40 Mbytes/s 80 Mbytes/s   The theoretical transfer rate of EIDE is up to 16.6 Mbytes/s in PIO mode 4 or multi DMA mode 2 (soon 33.3 Mbytes/s) with all the problems you may have already faced. Here you will find a table of several interfaces and their speeds. However, today's CD-ROM's often use PIO mode 3, while older device use PIO mode 0 to 2. Sometimes devices lie about the PIO mode they support. There are harddisks that say they are able to use PIO mode 2 but they only work reliably in PIO mode 1! Whenever you get errors accessing your Hard disk, try to lower the PIO mode first!   Possible theoretical transfer rates of the IDE bus (ATA) single word DMA 0 2.1 Mbytes/s PIO mode 0 3.3 Mbytes/s single word DMA 1, multi word DMA 0 4.2 Mbytes/s PIO mode 1 5.2 Mbytes/s PIO mode 2, single word DMA 2 8.3 Mbytes/s Possible theoretical transfer rates of the EIDE bus (ATA-2) PIO mode 3 11.1 Mbytes/s multi word DMA 1 13.3 Mbytes/s PIO mode 4, multi word DMA 2 16.6 Mbytes/s Possible transfer rates of Ultra-ATA (Ultra DMA/33) multi word DMA 3 33.3 Mbytes/s   It is not only the interface transfer rate that determines how fast a Hard disk is. How fast the data can be written or read from the media, e.g. data density and rotation speed is more important. The fastest interface can't do anything faster than the 'inner values' of a Hard disk are capable of. Today, most harddisks are still under 10 Mbytes/s transfer rate physically. A faster interface is advantageous on when data is read from or written to the cache in a multitasking environment with several devices accessed simultaneously. Multitasking environments especially benefit from SCSI, since simultaneous access occurs frequently. If you have a server or are working with large files like audio, video or disk-intense applications, you will benefit more from SCSI than EIDE. There are three reasons for this: All modern operating systems now supports SCSI very well. Windows 3.x didn't! Bus mastering really works better with a SCSI bus mastering controller. The fastest harddisks with the best performance are SCSI.   If you need large capacities and the highest transfer rates available on the market you need SCSI. This is not because EIDE is incapable of this, it’s because of the market. High-end disks with high capacities and high performance are intended to be used in servers and aren't build with EIDE interface. At the moment, EIDE disks are only built with up to a 5 Gigabyte capacity (there is a problem with a 4 GB barrier with some BIOS's again and for drives bigger than 8 GB you need a new BIOS that supports the INT 13 functions AH=41h bios 49h) and transfer rates of about 9 Mbytes/s. If you need more, you'll have to use SCSI. Also, SCSI harddisks have larger cache RAM than EIDE harddisks.   Performance, some thoughts You need to know how a slow or fast Hard disk affects your overall system performance in a standard environment. If your operating system isn't constantly swapping (e.g. you have enough memory) the speed of a Hard disk is only a small part of a well balanced system. Let’s say you have a Hard disk that has 30% better performance than another older one; the benefit for standard applications would be from 2% up to 18%. Sometimes, you want or need the fastest components available. Other times, more capacity and reliability is needed. There are several programs available that test the performance of a Hard disk. Some are crap, others are good. In any case, if you have one, you get numbers that tell you something. But do you have a point of comparison? Different benchmarks mean different numbers. Different environments mean different numbers. Modern benchmarks are independent from existing data on the Hard disk (only read performance testing can be done). But a benchmark could be affected by several things: To which channel is the Hard disk connected Is the Hard disk alone or together with other devices connected to the controller Under which operating system is the Hard disk tested and used Which drivers are loaded or not loaded. Testing at Monday or Friday etc.   The File System It is very important and I recommend you to go through my previous chapters again.   Upgrading Your Hard Disk Choosing a Disk Type There are many parts to a hard disk that a real "gear head" might argue are important in selecting a new drive. Most people really only use one criterion when considering which HD to choose: cost. You can get into a lot of trouble if that is your sole consideration, and I speak from experience. Here are the basic things to consider when comparing, in order of importance: Interface type, such as EIDE (Enhanced Integrated Drive Electronics). The interface type goes without saying. You wouldn't buy a SCSI (Small Computer System Interface) HD if all you have is an IDE controller, unless you want to add the benefits of a fast SCSI drive without eliminating the existing IDE drive. Also, make sure to match the controller with the drive. An Ultra Fast SCSI drive will not be "Ultra Fast" if you only use a SCSI 2 controller. The same can be said for an EIDE (Enhanced Integrated Drive Electronics) HD and an IDE controller. Maximum formatted storage capacity. HD manufacture's and vendors usually quote you the maximum storage capacity, which is always more than the formatted capacity due to many factors including file system (FAT16, FAT32, NTFS), cluster size or allocation unit, type of files being stored, and so on. Transfer rate. The transfer rate is the rate at which the drive and controller can send data to the system. The greater the value, the better. Ultra Fast Wide SCSI subsystems hold the current record at 40M/sec. Rotational speed (RPM). Rotational speed and transfer rates are closely related. The faster the RPM, the more data passes under the read/write head in a set period of time, allowing for higher total transfer. Faster is not always better, however. The faster the RPM, the more chance you have to drop some data. Not a problem for digital video, as in AV drives, but not so good for your spreadsheet. Average seek time (also known as access time). The access time is the amount of time that lapses between a request for information and its delivery. The lower the value, the better. Most modern HDs have an access time of 10ms or less. Cost per megabyte. This is a good way to compare two drives of different storage capacity. For example, the IBM 12G drive cost $349 (349/12,000M), which translates to about 3 cents per 1M. A 1G drive costing $99 ran me 10 cents per 1M; therefore, I'm getting a better deal with the larger drive even though it might cost me more. Onboard cache (or just cache). Onboard cache acts as a buffer for data being transferred to and from the HD. The larger, the better.   Adding a SCSI Drive to an IDE System If you would like to free yourself from the bindings that IDE imposes on you, but can't bear the idea of pitching a perfectly functional IDE drive, consider adding a SCSI drive as your upgrade instead of another IDE/EIDE drive. This will allow you to take advantage of the greater performance/expandability that SCSI has to offer, while retaining your current investment. And if you ever decide to invest in a new SCSI-based system, you can take the SCSI drives with you while retaining a completely functional IDE system. In an IDE/SCSI system, the IDE drive must be the boot drive. Very few computer systems have the ability to allow the SCSI drive as the boot drive with an IDE drive installed. Planning the Installation Once you have decided on the type of drive to buy (and you've picked out a controller, if necessary), it's time to plan your actual installation process. Drive upgrades are usually straightforward, but proper planning is the key to avoiding problems later on. Data Backups Before you attempt to perform any type of HD upgrade, you should perform a full system backup of your current hard disk's). If you are replacing a disk outright, a backup is vital for restoring your work to the new disk. If you are adding a second drive, a backup is not quite so critical, but will still protect you in the event you might accidentally lose data on your original disk. Backups can take many forms: you can use floppy disks, SyQuest cartridges, Iomega Zip or Jazz cartridges, or any type of tape drive. Most of these drives come bundled with some form of backup software, so once the "backup drive" is connected, you should be able to start the backup software and proceed almost automatically.   Power Considerations Power is the first issue to consider. A typical hard disk requires about 10 watts of power for proper operation. This may not sound like much, but you must be sure that your power supply is able to provide that much power. Otherwise, your supply may become overloaded. Overloaded supplies often cause unpredictable PC operation, or prevent the PC from booting at all. In extreme cases, a severely overloaded power supply can even break down. Here are some rules to help avoid power problems: If you're just replacing an existing hard drive with a new one, power should not be a problem. If your system has not been upgraded before, it can usually support an extra drive without any problem. If your system has been significantly upgraded already, pay attention to the system's operation after you add a new drive. If the system behaves erratically, you may need a higher voltage power supply. You also need to have a 4-pin power connector available for the new drive. If you're just replacing an existing hard disk outright, you can just reuse the power connector on the replacement drive. When adding a new drive, be sure that there is an extra power connector available from the power supply. If you don't have a power connector available, you can purchase a Y-connector that splits an existing connector into two separate connectors. You simply remove a power connector from a drive, install the Y-connector, plug one arm of the Y-connector back into the original drive, and you've got a spare connector for that new drive. Choosing a Drive Bay You also need to decide where your drive is going to go in the system. When replacing a drive outright, you can simply reuse the original drive bay. If you are adding a second hard disk, you need to locate an unused drive bay. Large desktop and tower chasses often have several drive bays available. You may have to hunt for an open bay in a mini-desktop enclosure. Drive bays are typically referred to as external and internal. External drive bays are located behind those plastic plugs you see on so many plastic housings. Floppy disks, CD-ROM drives, and tape drives all demand these external drive bays. Internal drive bays are little more than metal brackets inside the chassis where you can bolt a drive securely. Because you do not need to insert or remove anything from a hard disk, you can use external or internal drive bays. Most hard drives are 3 1/2 inches in size, so if you want to use a 5 1/2-inch bay, you need to use mounting brackets. These mounting brackets and slides usually come with the drive but can be purchased separately from a local computer store if necessary. Drive Configuration Configuration of your new hard disk is paramount to its proper function. Examine your new drive and locate any jumpers . For an IDE/EIDE drive, there are typically three ways to jumper the drive: As the only hard disk As the primary disk in a two-disk system As the secondary (slave) disk in a two-disk system If the hard disk is to be the only one in your system, the factory settings are usually correct. In this case, the jumper is not being used. You can skip to the next section. When you use the new disk as a secondary drive--that is, the second drive on the same ribbon cable--make sure it is jumpered as the slave drive, and set the original disk so that it is the master drive. This is the least intrusive method to adding a new disk to your system. You will still boot from the original drive with all files intact, but you just see an additional drive letter show up in your Windows 95 Explorer window (or File Manager if in Windows 3.x).  An EIDE controller can have two separate chains, each with its own master and slave drive for a total of four devices. Making the new drive the master can get a bit messy. Because the drive is new, it will not have an operating system on it and will not boot. On an IDE/EIDE system, the master drive (the C: drive) has to be the boot drive. Therefore, you have to reinstall your OS on the new drive in order to use the system. All files should still be intact on the original drive; it will just be the next logical drive, usually D:. To get around this limitation, install the new drive as the slave. Boot the system, and duplicate the entire old disk to the new one. Shut off the system and switch master/slave status. Reboot the system to test. If all works well, you can reformat the old drive and you are ready to rock. Is Your Controller IDE, or Is It EIDE? It's OK to use the same controller with the new drive, but unless the controller is an EIDE controller, you will not be able to take advantage of all the performance enhancements of your new drive. If your controller is embedded in the motherboard and you are not sure if it is IDE or EIDE, look for a Primary and a Secondary controller. If you have these two controller, it is EIDE; only EIDE supports four devices (two on each connection). If you only have one controller (IDE), check your BIOS (Basic Input Output System) setup to see if you can disable the on-board hard drive controller. If so, you can buy an EIDE controller card and use it instead. SCSI disks are a bit easier to configure because you need only select the proper device ID for the drive. By convention, the boot disk (the C: drive) in a SCSI system is set as ID0, and a second SCSI disk (the D: drive) can be set as ID1. If your new SCSI disk falls at the end of a SCSI bus, you also need to install a set of SCSI terminating resistors on the drive. Fortunately, SCSI kits typically include terminating resistors, and provide specific instructions on how to install the terminators. Make sure to check the installation manual that came with your SCSI controller card. It's not always simple to terminate a SCSI chain; it depends on the type of controller (for example, some controllers support both internal and external SCSI chains, and both need termination). NOTE: IDE/EIDE and SCSI hard disks can coexist in the same system, but you cannot boot a PC from a SCSI disk if there is an IDE/EIDE disk in the system as well. IDE/EIDE disks automatically take precedence. If you need to boot from a SCSI disk, you have to remove any IDE/EIDE disks from the system first. Installing a New Drive Now that you've determined what type of drive configuration you have in the previous section, you can install the new drive. This section is divided into similarly appropriate parts, with steps common to all new installations here. Before You Begin, You Need: A  screwdriver An open drive bay (either 51/4- or 31/2-inch) Slide rails 3 1/2- to 5 1/4-inch mounting brackets (if you are putting the drive in a 5 1/4-inch bay) Mounting screws (come with the drive) Proper length ribbon cable 1. Shut down, turn off, and unplug the PC. 2. Open the system. 3. Discharge your static. The following sections are specific to the type of drive configuration, and you should skip to the section that suits your needs.   Replacing an IDE Drive This section describes the process of replacing a drive in a single drive system. For information on adding a new drive, skip to the next section. TIP: It is highly recommended that you replace your old IDE controller with a new EIDE controller. The additional cost is more than worth it in performance gains. 1. Locate the old drive, unplug the power connector and the 40-pin ribbon cable     Remove the 4-pin power connector.     Remove the 40-pin IDE ribbon cable. 2. Locate and remove the mounting screws. These are found either on the side of the drive bay or in front      Remove the drive mounting screws. 3. Carefully slide the drive out, making sure not to snag any other cables or wires in the process. 4. Remove and save any mounting brackets, slide rails, and screws that may be attached. You can reuse them on the new drive. That's the surest way of getting a good fit.     Remove the old drive. 5. Attach any mounting brackets and/or slide rails from the last step to the new drive. 6. Check the position of the key in your 40-pin ribbon cable. This key assures the correct alignment of the cable to the drive. TIP: Don't panic if your ribbon cable does not have a key; not all do. There will be one colored wire at the side of the cable to indicate the #1 pin position, and the drive will also indicate this pin on its underside 7. Slide the new drive in place of the old one, and replace all mounting screws. CAUTION: When securing a hard disk, be extremely careful to avoid stripping or cross-threading a mounting hole. An unevenly mounted drive will vibrate excessively. This can lead to premature drive failure. 8. Reattach the ribbon cable, noting the position of the key, or the #1 pin position. 9. Reattach the 4-pin power connector. TROUBLESHOOTING: My system doesn't even start when I turn the power on. What happened? You may have inadvertently replaced the ribbon cable reversed (#40 wire to the #1 pin). Turn the power off and double-check that the #1 pin positions are lined up. Adding a New EIDE Drive This section describes the installation of an additional EIDE drive to a system with an IDE/EIDE drive already installed. This will be the most likely scenario because most people are unwilling--no matter how old and slow the old drive was--to simply discard it; it probably cost more than the new one! If this isn't you, you can skip to "Adding a New SCSI Drive" or back to "Replacing an IDE Drive." Follow these steps to add a new EIDE drive: 1. Locate an open drive bay for your new drive, preferably one as close to the original drive as possible. The reason for this is the limited distance between drive connectors on the ribbon cable. 2. Attach any mounting brackets and/or slide rails, as required by your particular case design, to the new drive and slide it into place. Note that some cases do not require any mounting brackets (3 1/2-inch bays) or slide rails. 3. Check to see if you have an available 4-pin power connector; most systems will have at least one or two spares. If not, you can purchase a Y-connector that will split the power off one of the other power connectors. 4. Attach the 4-pin power connector to the new drive. 5. Attach an available drive connector from the 40-pin ribbon cable--note the key in the connector and the notch in the drive to the new drive. NOTE: If you have an EIDE controller and the secondary IDE connector is unused, you can attach an additional 40-pin ribbon cable to it to control your new drive. In that case, the jumper settings on both the new drive and the old would be set to MASTER, because these controllers function as two separate controllers. The next device on either cable, whether hard disk or CD-ROM drive, would then be set to SLAVE. There you have it. A new drive is born. Now you are ready to move to the next phase, "Preparing and Formatting the Drive."   Adding a New SCSI Drive In this section, you learn how to add a new SCSI hard drive to your system. If you don't have to complete this task, skip to the next phase "Preparing and Formatting the Drive," or refer to the earlier sections "Adding a New EIDE Drive" or "Replacing an IDE Drive." About the Controller Card The actual process of installing the card is no different than any other expansion card you might add (see Chapter 6, "Basic Device Configuration and Installation"). Very few new motherboards come with an embedded SCSI controller, as EIDE does, and neither do most home systems you might want to upgrade. The first thing to note is that most SCSI controllers can have both an internal chain and an external chain, and both need to be terminated Most internal connectors appear similar to the IDE counterpart except bigger-- 50 pins instead of 40 pins. The exception is an Ultra Wide SCSI connector (16-bit path rather than the standard 8-bit) which is actually visually smaller but uses 68 pins. External connections can be different, too. Some older controllers use a 50-pin connector that resembles a parallel port. Most newer controllers use a 50-pin mini-connector or a 68-pin mini-connector for Ultra Wide. There are adapters available to change from one kind of connector to another, in the event a device you want to connect uses a different connection. Compatibility and Recommendations As you are beginning to see, there is not quite the same standardization in the SCSI world as there is in the IDE. This is one reason SCSI has been relegated to the world of the "high-end" machine or computer geek. Only these people were willing to take the time to understand all the factors necessary for a properly functioning SCSI subsystem. With this in mind, I recommend you purchase an Adaptec SCSI controller card because it is the most standardized SCSI board out there. In fact, Adaptec has been pushing the standardization of SCSI for years. The ASPI Advanced SCSI Programming Interface was once Adaptec SCSI Programming Interface, before they turned it over to public domain. There are other SCSI boards out there with as good, if not better, price/performance ratio, but the headache you could get with incompatibilities and poorly written device drivers isn't worth the difference. Also note that the SCSI board has its own connection for the LED lights that flicker on the outside of your case to let you know there is some hard drive activity going on. It's not necessary to connect this, but some people like to use these lights for diagnostic reasons, or just because it looks cool. Termination Termination is one of the most important factors in setting up your SCSI subsystem. In a nutshell, the last device on a SCSI chain--internal and external--needs to have termination enabled. This can be accomplished in different ways, depending on the device, but this fact holds true of all SCSI chains. For example, if you have only two devices--a controller card (yes, it counts as a device) and an HD--they both need to be terminated. It's usually automatic for the controller; you do not need to do anything (not always the case if you are not using an Adaptec controller, though). The HD will have either terminating resistors that plug into the underside of the drive or have a jumper/dip switch to set, as in the case of the IBM Ultrastar ES 2.16G Ultra SCSI hard disk I used in this upgrade. Now add another device to this party, like an internal SCSI CD-ROM drive. If you were to install it between the HD and the controller, no termination is necessary. On the other hand, if you installed it after the HD, you would need to remove the termination from the HD and terminate the CD-ROM drive. Got it? Think so, huh? Let's add an external scanner to this scenario. Both the scanner and the HD (or CD-ROM, in the last case) need to be terminated. Why? The controller card auto-terminates. In the case where the only devices were internal, the card was one terminator and the drive was the other. Both ends were terminated. When you added the external device, the controller card becomes non-terminated and the scanner becomes the other end of the chain. Now the scanner is one terminator and the internal drive is the other. Simple, right? The bottom line is you need two terminating devices in any SCSI chain--one at both ends. Setting SCSI IDs Each device on a SCSI chain has its own unique ID called its SCSI ID. You choose this ID either through jumpers or switches, and they can be set to any number from 0 to 7. This has no relation to the device's physical orientation on the SCSI chain, nor does it affect termination in any way. There are some general rules though: The boot disk is usually set to ID 0. The host adapter is usually set to ID 7. Some new SCSI devices are supporting SCAM (SCSI Configured Automatically), where the host adapter assigns the unique IDs at boot up automatically. If your devices support this, be sure to enable this feature in the host adapter's BIOS, as described in the next section. Configuring the Host Adapter The SCSI controller card (also known as the host adapter) uses its own BIOS, similar to the motherboard BIOS, to configure the devices under its control. These settings are different for each host adapter, but in general there are a few important features you should learn about that are common to all: Extended BIOS translation. Enabling this feature allows MS-DOS 5.0 and above, including Windows 95, to support drives larger than 1G. This option is not necessary under OS/2 or Windows NT. BIOS support for bootable CD-ROM. Enabling this feature allows you to boot your system from special bootable CD-ROMs. Plug and Play SCAM support. SCAM automatically assigns a unique SCSI ID to any device attached to the SCSI chain that supports this feature. Target Boot ID. This is the SCSI ID of the disk you want to boot from. With SCSI, you can choose which disk you want to boot from, unlike with IDE. Preparing and Formatting the Drive Now that you've installed your new drive, made all the proper connections, and replaced the case cover, you need to let the computer know the new drive is there. This is done through the BIOS Setup program. CMOS Considerations The CMOS (Complementary Metal-Oxide Semiconductor) is the chip that holds the information your motherboard's BIOS has recorded on it. Some people use these terms interchangeably. The BIOS reads the system information contained in the CMOS, and then checks out the system and configures it. Next, the BIOS looks for an operating system on the boot drive (drive 1 or C: drive), launches that OS, and then turns control over. Once the BIOS setup is activated, most new BIOS's have the IDE HDD Auto Detection option. This is a great improvement over older BIOS programs that required you to know things like the cylinders, heads, sectors, and so on. You need to go through this process so your computer can register the new drive and make it "visible" to your OS. In case you have one of these older BIOS's or the auto detect didn't correctly ID your drive, you need to enter this information manually. Your new drive will most likely have this configuration information printed on a label pasted to the top of the mounting chassis. You might also find the information on the manufacturer's WWW site. Here's a list of hard drive manufactures you can call: Conner 408-456-3200 IBM 914-765-1900 Maxtor 408-432-1700 Western Digital 714-932-5000 Quantum 408-894-4000 Seagate 408-438-8222 Because every BIOS works a bit different, you need to read the BIOS Setup instructions that came with your computer, but some general instructions follow: 1. Go to User Defined Settings. 2. Enter the parameters from your drive. Usually, only the Cyls (cylinders), Heads, and S/T (number of sectors per track) are necessary; landing zone and capacity are usually not required. The Meg field should then reflect the drives' unformatted capacity in megabytes. NOTE: Be sure to save your changes before exiting a CMOS Setup routine. If you forget to save, the new disk's parameters will be lost, and the drive will not be recognized. Translating BIOS It is important to note that not all older BIOS's will be able to recognize disk drives larger than 504M. Those that do are called translating BIOS's. Even if your BIOS correctly identifies the new drive's parameters, it doesn't mean the BIOS will translate those parameters. Here's how to check: 1. While at the BIOS Setup screen, look for a setting called LBA, Large Block Access, or Translation, and enable the option. 2. Check if the Auto configure Drive Type returns a heads value greater than 16; if so, you are probably OK. 3. Call your computer's vendor and/or manufacturer and ask. What do you do if you don't have a translating BIOS? You can upgrade your BIOS (see Chapter 7, "Working with the BIOS," for help), or you can use software utilities like EZ-Drive that comes with all Western Digital hard drives over 528M (which is all of them these days), or Ontrack Disk Manager. The software works; I've used it. It does have some limitations, so read the instructions carefully and weigh these limitations against the cost of an upgraded BIOS. Next task is to format the drive and done.   Return to Menu