One of the key components in keeping the system up-to-date is the hard disk drive (HDD). Software manufacturers continue to produce larger and larger programs. In addition, the types of programs found on a typical PC are expanding. Many newer programs place high demands on the hard drive to feed information, such as large graphics files or digitized voice and video, to the system for processing.
Invariably, the system will begin to produce error messages saying that the hard drive is full. The first line of action is to use software disk utilities, such as Checkdisk, Scandisk, and Defrag, to optimize the drive's organization. The second step is to remove unnecessary programs and files from the hard drive. Programs and information that is rarely, or never, used should be moved to an archival media, such as removable disks or tape.
In any event, there may come a time when you need to determine whether the hard drive needs to be replaced to optimize the system's performance. One guideline suggests that the drive should be replaced if the percentage of unused disk space drops below 20%.
Another reason to consider upgrading the HDD involves its capability to deliver information to the system. If the system is constantly waiting for information from the hard drive, replacing it should be considered as an option. Not all system slowdowns are connected to the HDD, but many are. Remember that the HDD is the mechanical part of the memory system; everything else is electronic.
As with the storage space issue, HDD speed can be optimized through software configurations, such as a disk cache. After it has been optimized in this manner, however, any further speed increases must be accomplished by upgrading the hardware.
When considering an HDD upgrade, determine what the real system needs are for the hard drive. Multimedia-intensive applications can place heavy performance demands on the hard disk drive to operate correctly. Moving large image, audio, and video files into RAM on demand requires high performance from the drive. Critical HDD specifications associated with disk drive performance include the following:
Access time. The average time, expressed in milliseconds, required to position the drive's read/write (R/W) heads over a specified track/cylinder and reach a specified sector on the track
Track seek time. The amount of time required for the drive's R/W heads to move between cylinders and settle over a particular track following the Seek command being issued by the system
Data transfer rate. The speed, expressed in megabytes per second (MBps), at which data is transferred between the system and the drive
These factors should be checked thoroughly when upgrading an HDD unit for speed-critical applications. In contemporary systems, the choice of hard drives for high-performance applications alternates between Integrated Drive Electronics (IDE)/Enhanced IDE (EIDE) drives and Small Computer System Interface (SCSI) drives. The EIDE drives are competitive and relatively easy to install; the high-end SCSI specifications offer additional performance, but require additional setup effort and an additional host adapter card.
Before upgrading the HDD unit, make certain the existing drive is providing all the performance it can. Check for SMARTDRV or VCACHE arrangements at the software configuration level and optimize them if possible. Also, determine how much performance increase can be gained through other upgrading efforts (see the "System Board Upgrading" section, above) before changing the hard drive.
If the drive is being upgraded substantially, such as from a 500MB IDE drive to a 10GB EIDE drive, check the capabilities of the system's ROM BIOS. If the BIOS does not support LBA (logical block addressing) or ECHS (Enhanced Cylinder Head Sector) enhancements, the drive capacity of even the largest hard drive is limited to 528MB.
Be aware that the BIOS might be a size-limiting factor in disk drive partition sizes.
Finally, determine how much longer the unit in question is likely to be used before being replaced. If the decision to upgrade the HDD stands, ultimately, the best advice is to get the biggest, fastest hard drive possible. Don't forget to consider that a different I/O bus architecture could add to the performance increase.
This article has covered upgradeable components found in common PC systems, including information about when and how to upgrade them. By reviewing this information and paying special attention to the "Test Tip" boxes, you should be well prepared for questions on Objective 1.8 in the exam's Core Hardware module.