Howard Anderson

2 – The internet

Publisher Summary The net is a powerful tool and a huge resource for troubleshooting information. Since the Internet is not one “thing”, some means are required to find what one needs. There is no central index so various people have devised ways to create indexes of Internet resources. These indexes are never complete so items will be “on the Internet” but not indexed, they are there but search engines will not find them. Since there is no central index, various people have devised ways to create indexes of Internet resources. Most people use search engines to find what they want on the net. Many have a favorite search engine on the grounds that it gives them what they want. The performance of a search engine depends critically on how well these indexes are built. It is also very important to remember that the whole business of search engines is in a state of constant change. The chapter focuses on how to search the Internet.

Troubleshooting windows registry

This chapter provides some starting points for troubleshooting Windows. All versions of Windows (except 3.1) use a large database of system information called the registry. This database is updated all the time, especially when software is installed. It stores settings, configurations, and related data and is central to the way Windows works. If it becomes corrupted in any way, Windows will fail to load or run successfully. One should suspect registry trouble if Windows does not start after installing a new or updated piece of software. The registry can be backed up and restored to overwrite a corrupted version but the method used to achieve this is different in the various versions of Windows. The registry in Windows XP is well protected so should not need to be manually edited; however, trouble can result from failed installations, bad, or corrupted drivers. Drivers for XP are “digitally signed” to prove they have passed reliability tests set by Microsoft, so should not give trouble.

Hard disk drives

This chapter provides an overview of hard disk drives. The hard drive in a PC employs a rotating disk or disks. These disks are coated with a material that has certain persistent magnetic properties required to store data as 1s and 0s. Hard disk drives have a boot record that occupies the very first sector of the disk. On hard disks, this is known as the “master boot record”. The master boot program copies itself to a different location in memory and then inspects the partition table looking for a startable partition. If more than one startable partition exists or any boot indicator is not 80 or 0 then DOS will display an “invalid partition table” error message. Failure of one or more of the read/write heads, the drive electronics, the voice coil actuator, or a major problem with one or more of the disk surfaces can render a hard disk drive inoperable. While many of these faults are actually quite simple, specialist tools, test facilities, and a “clean area” are essential if a hard drive is to be successfully repaired.

Troubleshooting windows error messages

The problems that can occur in Windows can be arranged into the categories: invalid page faults, general protection faults, fatal exceptions, protection errors, and kernel errors. The modern CPUs are designed to detect situations in which an executable program attempts to do something that is nonsensical or “invalid” in terms of the hardware and software configuration of the system. The most common problems are stack faults, invalid instructions, divide errors, and general protection faults. Windows Protection error messages occur when a computer attempts to load or unload a virtual device driver (VxD). This error message is a way to let a user know that there is a problem with the device driver. The diagnostic tool, Dr Watson, is supplied as part of the Windows operating system that generate a snapshot of the current software environment, which can provide invaluable information of what was happening at the point at which the fault occurred.

The PC expansion buses

The availability of a versatile expansion bus system within the PC must surely be one of the major factors in ensuring its continuing success. The bus is the key to expansion allowing one to painlessly upgrade a system and configure it for almost any conceivable application. A number of standards are employed in conventional PC expansion bus schemes, ranging from the original Industry Standard Architecture (ISA) to peripheral component interconnect (PCI) and the advanced graphics port (AGP). The PCs ISA bus is based upon a number of expansion “slots” each of which is fitted with a 62-way direct edge connector together with an optional subsidiary 36-way direct edge connector. Trouble with PCI devices can be caused by: software bugs, software settings, hardware faults, and device conflicts. The standard way to fix software bugs is to obtain the latest card driver from the manufacturer. The main use of AGP—a bus specification for graphics adapters—is to enable 3-D graphics to display quickly on PCs. Most trouble associated with the AGP has nothing to do with the AGP itself, it is more likely to be with the graphics card or the monitor, especially with software/driver settings.

The serial communication ports

The PCs serial communication ports (COM1 and COM2) were once the means of linking a PC with the rest of the world. Modern machines use much faster connections such as USB but there are many legacy devices that use the serial port to connect to the PC. The serial port standard is known as recommended standard (RS)-232C. The standard relates essentially to two types of equipment: data terminal equipment (DTE) and data circuit terminating equipment (DCE). Data terminal equipment (is capable of sending and/or receiving data via the COM1 or COM2 serial interface. Data circuit terminating equipment facilitates data communications such as a typical modem (modulator–demodulator) forming an essential link in the serial path between a PC and a telephone line. A PC serial interface is usually implemented using a standard 25-way D connector. The PC (the DTE) is fitted with a male connector and the peripheral device (the DCE) normally uses a female connector. When one needs to link two PCs together, they must both adopt the role of DTE while thinking that the other is a DCE. This chapter explains the troubleshooting process for communication ports.

Printers and the printer interface

The PCs parallel ports (LPT1 and LPT2) provide a very simple and effective interface that can be used to link a PC to a wide range of printers and other devices such as external tape and disk drives. Parallel I/O is used to transfer bytes of data at a time between a microcomputer and a peripheral device (such as a printer). Several control signals are present in order to achieve “handshaking”—a process that controls the exchange of data between the computer system and the printer. The Centronics interface has become established as the most commonly used interface standard for the transfer of data between a PC and a printer. The standard employs parallel data transmission (a byte is transferred at a time) and is based on a 36-way Amphenol connector. This chapter explains the principles of parallel I/O, the Centronics interface standard, and the basic fault finding and troubleshooting procedures that can be applied to the parallel interface.

6 – Semiconductor memory

Publisher Summary This chapter examines the use of random access memory (RAM) and read only memory (ROM) within the PC. It also explains how one can locate and replace a faulty memory chip. Each location in semiconductor ROM and RAM has its own unique address. Each ROM and RAM accounts for a particular block of memory depending upon the capacity of the ROM or RAM in question. The BIOS ROM that contains the low-level code required to control the systems hardware is programmed during chip manufacture. Computers work by executing instructions from RAM so the speed of RAM is a very important factor in the performance of the whole machine. Dynamic RAM (DRAM) is the oldest type that stores each bit in a storage cell as an electrical charge, which must be refreshed every few milliseconds to retain the information. Extended data out RAM (EDO RAM) is faster than DRAM and extends the time that output data is valid.

3 – Microcomputer fundamentals

Publisher Summary An understanding of the basic operation of a microcomputer system is an essential first step to getting the best out of the PC. This chapter provides the basic underpinning knowledge required to carry out successful upgrading and troubleshooting. The microprocessor is crucial to the overall performance of the system. In a microcomputer a single VLSI microprocessor chip provides the functions of the CPU. The basic components of a simple microcomputer system, the CPU, RAM, ROM, and I/O system, are linked together using a multiplewire connecting system known as a “bus”. A control signal of particular note, “interrupt” provides an efficient means of responding to the needs of external hardware, such as a keyboard or a modem connected to the serial port. The operating system provides an essential bridge between the users application programs and the system hardware. In order to provide standardized environment (which will cater for a variety of different hardware configurations) and ensure a high degree of software portability, part of the operating system is hardware independent.

9 – Replaceable disk drives

Faster devices have largely superseded floppy disks but there is still a demand for their use. PCs without floppy drives are still not common except in corporate networks. Most if not all floppy disks are now the 1.44 MB format 3.25” disks. This chapter introduces the most commonly used floppy disk formats and the structure of boot records and file allocation tables (FAT). It also describes the floppy disk interface and the functions of the PCs floppy disk controller (FDC). Floppy disks can be formatted as “bootable” or data only. The boot record contains a number of useful parameters and may contain code that will load and run. Bootable disks must also contain two other programs: IBMIO.COM and IBMDOS.COM (or IO.SYS and MSDOS.SYS). These, in turn, are responsible for locating, loading, and running the command interpreter. Fault diagnosis within floppy disk drives should only be carried out when one is certain that the disk interface and controller can be absolved from blame. Thus, whenever the drive in a single-drive system is suspect, it should first be replaced by a unit that is known to be good.