A car can be running, but it might not be running at its optimum level if it needs adjustments or if you don’t perform routine maintenance. The same can be said for a computer system. Even when running correctly, PCs require tuning to achieve optimum performance. As a PC runs, its performance can suffer over time, and you must perform routine maintenance to return the unit to a peak operating level. The two most-used resources, and therefore the most common causes of a system bottleneck, are the hard drive and RAM configuration. Another problem, the I/O card configuration, can be avoided by installing the I/O cards in the proper order.
I/O Cards
When configuring a system, remember that PCI cards have a more direct means of obtaining processor time than local bus or ISA bus cards, and that newer, AGP video adapters are built to operate more efficiently with Intel Pentium MMX technology. The MMX technology has circuitry that interacts with AGP video cards to render 3-D images on the screen much more quickly. PCI bus cards operates at a faster speed (100 MHz bus speeds are available) than ISA or local bus cards, and the data path is wider, so throughput is dramatically increased.
When configuring a system’s hardware, try to use as many PCI cards as possible. Video adapters, network adapters, modems, and sound cards are available in a PCI format. If all the I/O cards are PCI, place the video adapter in the first slot, followed by the network interface, then the modem and/or sound card. The slots are serviced in order on the PCI bus and the video card is the busiest I/O card in your system.
If possible, you should avoid installing any ISA cards in a system with PCI cards. ISA cards are serviced not by slot order, but by IRQ number. As you recall from Chapter 2, the order IRQs are serviced in are IRQ0, IRQ1, IRQ2, IRQ8, IRQ9, IRQ10, IRQ11, IRQ12, IRQ13, IRQ14, IRQ15, IRQ3, IRQ4, IRQ5, IRQ6, and IRQ7. Typically, the interface cards are configured to certain IRQs from the factory (as discussed in Chapter 1) and these configurations let the system operate as efficiently as possible, but knowing the order IRQs are serviced in allows the technician to configure the I/O cards to match the system’s normal usage needs.
Hard Drives
Two of the easiest ways to optimize hard drive performance are to ensure that the drive and its controller work together efficiently and to avoid or correct fragmentation.
Older hard drive controllers could not accept data as quickly as the drive could provide the data, so the interleave setting on the drive was critical to peak performance of the disk system. The interleave of the drive determines the number of sectors that are skipped between read or write cycles for the drive. For example, when the interleave ratio is set to 2:1, a sector of data is written and then the next two sectors are skipped before a write operation will take place again. In this way, when data is read, the hard disk will be positioned over the needed data by the time the controller is ready to accept data again. If the interleave is set to a smaller ratio, the disk will go an entire revolution before the heads are positioned over the data the controller needs again. If the interleave is set to a larger ratio, the controller is idle, waiting for the drive to pass unwritten sectors before the data is reached.
If you’re installing an older disk drive, verify that the interleave setting is correct for the hard drive controller being used. The interleave setting is configured during the low-level format phase of disk preparation. All new SCSI controllers and IDE interfaces are fast enough to accept data with the interleave setting set to a 1:1 ratio, and the low-level format is performed in the factory, so this setting is already configured correctly. The interleave setting is a concern only with older-technology disk drives.
As data is retrieved from the disk and rewritten to the disk, the data can become fragmented, and the overall operation of the PC can slow down. When a program needs disk space, the system allocates the disk space in clusters. As changes are made to a data file — when another page of text is added to a document — the data file needs more space and requests another cluster or several clusters of space. Many times, contiguous clusters (clusters next to the current data clusters) are not available, so the file is placed in different locations across the surface of the disk. When the file is recalled, the system must retrieve the data file from several locations on the surface, which slows down the retrieval process.
Utilities are available to defragment a drive. These utilities reallocate clusters so that files have contiguous space. When a defragmentation program is run, the utility can be set to defrag just data files or both data and application files. Relocating application files to the clusters that the hard drive can access most quickly also speeds up performance. However, many copy-protected programs place data in clusters that cannot be reallocated. The defragmentation program recognizes clusters that cannot be relocated and does not attempt to move them. Defragmenting programs are covered in later chapters.
RAM
RAM configuration is critical to proper operation. The types of RAM used by the system are conventional, upper, and extended memory. When MS-DOS first came out, the operating system could address only 640K of memory space; therefore, everything that occurred on the system occurred in that 640K area. As technology improved, the hardware increased in capacity and the operating system and add-on components, such as sound cards, became larger and more powerful — and took up more space in RAM. Therefore, less RAM was left available for applications to run in.
MS-DOS was rewritten to allow a portion of MS-DOS and the device drivers to be loaded into upper memory (the memory between 640K and 1 MB), thereby leaving more space open for applications to run in. The appropriate utility for DOS 6.x is Memmaker; it configures the operating system and device drivers to use the upper memory. The Memmaker utility is covered in detail in later chapters.
REVIEW
In this chapter, you learned to use logical troubleshooting techniques to diagnose and troubleshoot a system problem. The areas that can affect the operation of a PC include the working environment, user-generated problems, hardware, and software failures.
Examples of environmental problems include no AC power, changes in the temperature causing a change in the humidity level, and location of equipment. Examples of user-generated problems include addition of new equipment or software. Hardware failures typically cause the system not to boot properly, if at all; they can also cause some operational component of the PC to fail.
Logical troubleshooting techniques can be used to isolate a pinpoint these types of failures. Software diagnosis and troubleshooting will be covered in a later chapter.
When equipment fails to operate properly, the POST generates audio and/or visual error codes. Typically, when a system passes the POST, the response is no beep, one short beep, or two short beeps, depending on the BIOS manufacturer. A series of short and long beeps typically indicates the failure of a core component. On-screen codes can also be generated by the POST and point to the failure of a particular core component, but they can be seen only if the video subsystem is operational.
Some of the standard hand tools you’ll need to repair a PC include nut drivers, Phillips and straight-slot screwdrivers, IC removal and insertion tools, and a digital multimeter (DMM). Multimeters measure electrical voltage, resistance, and current.
Several DOS utilities can be used to prepare new hardware that is installed. To configure the memory for optimum performance use the Memmaker utility, which reconfigures memory usage.
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