Description: The hard disk drive is the "data center" of your PC--it holds all of your programs and data. The CPU may be the "brain" of your system, but if so, the hard drive is its memory and personality--it is what makes your PC what it is. Few of us could imagine using a PC without a hard disk drive; it's a defining component of the modern PC.
Role and Subsystems: The hard disk is a key component in the storage subsystem. It plays an important role in the performance, capacity and software support of the PC. Its quality and reliability is probably more important than that of any other component, since it is the only component that you cannot just swap out with another of the same type in the event of failure--you lose your data in the process. It therefore commands significant attention, or at least, it should!
Related Components: The hard disk must be matched to several other components in the system. First, it must be of a form factor compatible with the system case. Second, it must use the same interface as the controller or controllers within the PC. Finally, the selection of hard disk interface will have an impact on the selection of other storage subsystem components such as the CD/DVD drive. Usually the interface is chosen for the system and the hard disk selected to match it. Most systems use IDE/ATA, for which controllers are provided on the motherboard and no other components are necessary for compatibility. System case compatibility is also fairly universal.
Key Compatibility Selection Criteria: There are several important criteria to keep in mind when selecting a hard disk to suit your system, but most systems use standard hardware, making it actually fairly easy to find hardware that will suit your needs:
Form Factor: Hard disks come in several different common sizes, matched to the bays in the system case where they are installed. For most desktop PCs, the standard is the 3.5" wide form factor (actually about 4" wide, but that's the name). Standard hard disks are called slimline drives and are 1" in height. For notebooks the standard is the 2.5" form factor. Most hard drives sold for PCs, and almost all for regular consumer PCs, are 3.5" slimline units.
Interface Type: Most hard drives use the IDE/ATA interface; others, especially in high-end systems, use the SCSI interface. Those two cover 99% of the drives in desktop PCs, though there are some external drives that interface through the parallel, USB, or PC Card ports (they are used more for notebooks than desktops, actually). For most systems, you want an IDE/ATA hard disk. If you decide to buy or build a SCSI system, you need to purchase a SCSI host adapter, and make sure that you get matching drives that use a "flavor" of SCSI that the host adapter supports.
Spindle Speed Support and Cooling: Some high-speed drives generate a significant amount of heat and may require special cooling. Some system cases, especially smaller ones, may not be able to use these faster drives without problems. Fortunately most newer drives have largely addressed these heat issues.
Performance and Capacity Selection Criteria: There are many different performance issues related to hard disks. I discuss them in gory detail here, but for selecting a new hard drive I can boil the capacity and performance issues down to the following key points:
Capacity: Obviously, the size of the drive is an important consideration: bigger drives hold more. At the same time, don't overspend on an enormous drive unless you do a lot of downloading or working with large graphics, audio and video files. For "typical" PC uses a 50 GB drive will remain mostly empty for most people. (Of course, every time I think "drives are now big enough", a few years later I find that I'm wrong as I find new ways to fill them up!)
Spindle Speed: One of the most important differentiators between different drive models from a performance standpoint is the speed at which the spindle spins (and thus the data platters as well). For IDE/ATA, the fastest drives spin at 7,200 RPM; slower ones go at 5,400 RPM or even 4,400 RPM. Faster drives provide both higher transfer rates and faster random access to your data. For SCSI, faster 10,000 RPM and even 15,000 RPM drives are available (at a significantly higher cost, of course).
Seek Time: This specification, given in milliseconds, refers to how quickly the hard disk's actuator (the device that moves the head assembly) can position the heads to a random place on the surface of the disk platters. It is a very important performance specification; the lower the number the better and even differences of 1 millisecond can make a difference in performance in some situations.
Areal Density: This specification refers to how much data the drive packs onto each of its platters. It can be found listed in the product manual for the drive, or you can sometimes estimate it for comparing drives of the same form factor by dividing the size of the drive by the number of platters inside the drive. For example, the largest of the Maxtor DiamondMax 80 series of drives packs 80 GB onto four platters, giving it a rough-cut density of 20 GB per platter. Newer drives pack data more densely, improving both capacity and performance. (Note that some drive sizes in a family may use half of one platter or even some other fraction, so be careful in doing these calculations).
Sustained Transfer Rate: This specification indicates how fast the drive can stream data off the surface of the platters during sustained reads of many megabytes of data in a row. The higher this figure the better, but small differences between models usually aren't significant. It is most important for those working with large files.
Interface Speed: Both IDE/ATA and SCSI operate at several standard speeds. For IDE/ATA drives the current standard is Ultra ATA/100, with the "100" standing for the interface's maximum potential throughput, 100 MB/s. In theory, faster interface drives are better, but for most PCs the speed of the interface has little impact on overall hard disk performance, as long as the number is above the maximum sustained transfer rate of the drive (see under "magic numbers" below for more). If you want to run an Ultra ATA/100 drive you need a controller that supports Ultra ATA/100, but even a controller that runs at 66 or 33 MB/s theoretical bandwidth will work OK; the drives are backward compatible. Performance Impact: The hard disk is a very important performance component within the PC. The reason it impacts performance so substantially is that it is a mechanical component, and is therefore thousands of times slower than other key performance components such as the CPU and system memory, which are purely electronic. Upgrading to a newer hard disk can noticeably improve overall system performance.
Retail, OEM and Gray Market Issues: Hard disks are commonly sold in either retail or OEM packaging, and there are important differences between them. For starters, retail drive packages usually come with an installation kit, including a cable, mounting screws, jumpers, and a driver disk; OEM drives usually just come as a bare drive. You may need the retail package in order to easily install some drives, though the hardware is inexpensive and the drivers available from the manufacturer's web site in most cases.
The bigger issue is related to the warranty. Some manufacturers will provide no warranty support on OEM drives (which is why they are cheaper). Others provide a three-year or five-year warranty on all their drives, OEM or retail (but for these OEM drives are often not cheaper--TANSTAAFL). Most manufacturers will also refuse to provide warranty coverage on gray market drives. Be sure to shop around, as in many cases retail-packaged drives can be found for only a few dollars more than OEM drives.
Role and Subsystems: The hard disk is a key component in the storage subsystem. It plays an important role in the performance, capacity and software support of the PC. Its quality and reliability is probably more important than that of any other component, since it is the only component that you cannot just swap out with another of the same type in the event of failure--you lose your data in the process. It therefore commands significant attention, or at least, it should!
Related Components: The hard disk must be matched to several other components in the system. First, it must be of a form factor compatible with the system case. Second, it must use the same interface as the controller or controllers within the PC. Finally, the selection of hard disk interface will have an impact on the selection of other storage subsystem components such as the CD/DVD drive. Usually the interface is chosen for the system and the hard disk selected to match it. Most systems use IDE/ATA, for which controllers are provided on the motherboard and no other components are necessary for compatibility. System case compatibility is also fairly universal.
Key Compatibility Selection Criteria: There are several important criteria to keep in mind when selecting a hard disk to suit your system, but most systems use standard hardware, making it actually fairly easy to find hardware that will suit your needs:
Form Factor: Hard disks come in several different common sizes, matched to the bays in the system case where they are installed. For most desktop PCs, the standard is the 3.5" wide form factor (actually about 4" wide, but that's the name). Standard hard disks are called slimline drives and are 1" in height. For notebooks the standard is the 2.5" form factor. Most hard drives sold for PCs, and almost all for regular consumer PCs, are 3.5" slimline units.
Interface Type: Most hard drives use the IDE/ATA interface; others, especially in high-end systems, use the SCSI interface. Those two cover 99% of the drives in desktop PCs, though there are some external drives that interface through the parallel, USB, or PC Card ports (they are used more for notebooks than desktops, actually). For most systems, you want an IDE/ATA hard disk. If you decide to buy or build a SCSI system, you need to purchase a SCSI host adapter, and make sure that you get matching drives that use a "flavor" of SCSI that the host adapter supports.
Spindle Speed Support and Cooling: Some high-speed drives generate a significant amount of heat and may require special cooling. Some system cases, especially smaller ones, may not be able to use these faster drives without problems. Fortunately most newer drives have largely addressed these heat issues.
Performance and Capacity Selection Criteria: There are many different performance issues related to hard disks. I discuss them in gory detail here, but for selecting a new hard drive I can boil the capacity and performance issues down to the following key points:
Capacity: Obviously, the size of the drive is an important consideration: bigger drives hold more. At the same time, don't overspend on an enormous drive unless you do a lot of downloading or working with large graphics, audio and video files. For "typical" PC uses a 50 GB drive will remain mostly empty for most people. (Of course, every time I think "drives are now big enough", a few years later I find that I'm wrong as I find new ways to fill them up!)
Spindle Speed: One of the most important differentiators between different drive models from a performance standpoint is the speed at which the spindle spins (and thus the data platters as well). For IDE/ATA, the fastest drives spin at 7,200 RPM; slower ones go at 5,400 RPM or even 4,400 RPM. Faster drives provide both higher transfer rates and faster random access to your data. For SCSI, faster 10,000 RPM and even 15,000 RPM drives are available (at a significantly higher cost, of course).
Seek Time: This specification, given in milliseconds, refers to how quickly the hard disk's actuator (the device that moves the head assembly) can position the heads to a random place on the surface of the disk platters. It is a very important performance specification; the lower the number the better and even differences of 1 millisecond can make a difference in performance in some situations.
Areal Density: This specification refers to how much data the drive packs onto each of its platters. It can be found listed in the product manual for the drive, or you can sometimes estimate it for comparing drives of the same form factor by dividing the size of the drive by the number of platters inside the drive. For example, the largest of the Maxtor DiamondMax 80 series of drives packs 80 GB onto four platters, giving it a rough-cut density of 20 GB per platter. Newer drives pack data more densely, improving both capacity and performance. (Note that some drive sizes in a family may use half of one platter or even some other fraction, so be careful in doing these calculations).
Sustained Transfer Rate: This specification indicates how fast the drive can stream data off the surface of the platters during sustained reads of many megabytes of data in a row. The higher this figure the better, but small differences between models usually aren't significant. It is most important for those working with large files.
Interface Speed: Both IDE/ATA and SCSI operate at several standard speeds. For IDE/ATA drives the current standard is Ultra ATA/100, with the "100" standing for the interface's maximum potential throughput, 100 MB/s. In theory, faster interface drives are better, but for most PCs the speed of the interface has little impact on overall hard disk performance, as long as the number is above the maximum sustained transfer rate of the drive (see under "magic numbers" below for more). If you want to run an Ultra ATA/100 drive you need a controller that supports Ultra ATA/100, but even a controller that runs at 66 or 33 MB/s theoretical bandwidth will work OK; the drives are backward compatible. Performance Impact: The hard disk is a very important performance component within the PC. The reason it impacts performance so substantially is that it is a mechanical component, and is therefore thousands of times slower than other key performance components such as the CPU and system memory, which are purely electronic. Upgrading to a newer hard disk can noticeably improve overall system performance.
Retail, OEM and Gray Market Issues: Hard disks are commonly sold in either retail or OEM packaging, and there are important differences between them. For starters, retail drive packages usually come with an installation kit, including a cable, mounting screws, jumpers, and a driver disk; OEM drives usually just come as a bare drive. You may need the retail package in order to easily install some drives, though the hardware is inexpensive and the drivers available from the manufacturer's web site in most cases.
The bigger issue is related to the warranty. Some manufacturers will provide no warranty support on OEM drives (which is why they are cheaper). Others provide a three-year or five-year warranty on all their drives, OEM or retail (but for these OEM drives are often not cheaper--TANSTAAFL). Most manufacturers will also refuse to provide warranty coverage on gray market drives. Be sure to shop around, as in many cases retail-packaged drives can be found for only a few dollars more than OEM drives.
No comments:
Post a Comment