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Newbie Guides 
Beginners Corner
PC Hardware Reference
Part 3
The PC hardware reference guide is in three parts.
PC Hardware Reference Guide - Part 3
Tutorial Quick Links:
Installation, Configuration and Upgrading
Diagnosing and Troubleshooting
Safety and Preventative Maintenance
Part 2
Motherboard, Processors and Memory
Printers
Part 3
Portable Systems
DOS and Windows
Portable Systems
This section is concerned with the knowledge of Portable Computers and
there hardware.
Battery Types and Installation:
Nickel Cadmium (NiCad) Low Power, Long Charge Time, Memory
Nickel Metal Hydride (MiMH) Medium Power, Shorter Charge Time, No Memory
Lithium Ion (L-ION) Good Power, Short Charge Time, Light, No Memory,
Expensive.
Portable Displays
Older portables use CRT's Very Bulky, Heavy and poor quality. Nowadays
Liquid Crystal Displays (LCD) are used. These are flat and lightweight.
There are two major types of LCD screens:
- Passive Matrix(Dual Scan) - Very Common, Low power but lower quality.
Uses a grid of horizontal and vertical wires. These have problems with
moving images and display ghosting.
- Active Matrix(TFT) - Based on Thin Film Transistor (TFT) where a transistor
is at every pixel. Allows a much quicker refresh but uses more power.
Comparable in quality to a CRT.
LCD Displays are not serviceable but may be cleaned with specialist cleaning
materials.
PCMCIA and PC Cards
PCMCIA or PC Card is a standard interface to add credit card sized
peripherals to PC's. Three versions are now available.
- PCMCIA type I - Only used for memory cards. 68 Pin.
- PCMCIA type II - Used for I/O devices such as Modems or Network Cards.
- PCMCIA type III - Used for rotating mass storage such as hard drives.
DOS/WINDOWS
DOS System Files:
DOS System files consist of:
- AUTOEXEC.BAT - Located in the Root and automatically executed at start-up.
Runs Programs (Prompt, WIN, CLS etc) and set commands (Path, Comspec
etc..). Also calls other batch files. This is not required for OS Start-up.
- CONFIG.SYS - Located in the Root and automatically loaded by MSDOS.SYS.
This loads low level device drivers for hardware and memory drivers
such as HIMEM.SYS and EMM386.EXE. This is not required for OS Start-up.
- IO.SYS - Located in the Root and defines basic Input/Output routines
for the processor. Is Hidden and Read Only. This IS required for OS
start-up.
- MSDOS.SYS - Located in the Root and defines system file locations.
Is Hidden and Read Only. This IS required for OS start-up.
- COMMAND.COM - This is the command specifier. It is responsible for
the command prompt and contains all the internal commands such as DIR,
COPY, and CLS. Located normally in the Root directory but can be located
elsewhere and specified in the Autoexec.bat with a "SET COMSPEC=". This
carries no attributes and is required for OS start-up.
- HIMEM.SYS - Controls Extended Memory management in the extended memory
area. Located in C:\DOS and is not required for OS start-up.
- EMM386.EXE - Controls Expanded memory in the upper memory area. Located
in C:\DOS and is not required for OS start-up.
- ANSI.SYS - Located in C:\DOS and is used by CONFIG.SYS if required
to load a character set. Not required for System Start-up.
WINDOWS 3.x
Windows 3.x System files consist of:
- WIN.INI - Contains configuration information for Windows Applications.
An ASCII text file located in the C:\WINDOWS directory. Looks after
printing as well. Can cripple the system.
- SYSTEM.INI - Contains specific system and hardware settings for windows.
An ASCII text file located in the C:\WINDOWS directory. Errors can cripple
or make Windows inoperable.
Three files make up the Windows core components: Kernel, User, and GDI.
The kernel files (KRNL286.EXE or KRNL386.EXE) control and allocate all
the computer resources to manage memory, load applications, and schedule
program execution and other tasks.
- USER.EXE - creates and maintains windows on the screen, carrying out
all requests to create, move, size, or remove a window. USER.EXE also
handles requests regarding the icons and other components of the user
interface. USER.EXE directs input to the appropriate application from
the keyboard, mouse, and other input sources.
- GDI.EXE - controls the Graphics Device Interface, which executes graphics
operations that create images on the system display and other devices.
- WIN.COM - This is the actual file that runs Windows 3.x. It is made
during install and cannot be found on any installation disk.
WIN.COM performs three functions.
- Find out what processor is in the computer.
- Switch to the appropriate graphics mode and display the *.LGO file.
- Load the Windows Graphics Advert. This is an .RLE file.
WINDOWS 95:
Windows 95 System files consist of:
- IO.SYS - Same as for DOS. This is because WINDOWS 95 is bootable.
- MSDOS.SYS - Same as for DOS but doesn't contain system code.
- COMMAND.COM - Same as for DOS.
- WIN.INI - For 16-bit compatibility.
- SYSTEM.INI - For 16-bit compatibility.
- SYSTEM.DAT - Hardware related Registry.
- USER.DAT - User related Registry.
OS Start-up Environments
Windows 3.x:
- DOS loads first.
- User enters WIN.COM
- WIN.COM checks Processor, Graphics Mode , Loads Banner then passes
to WIN386.EXE
- WIN386.EXE switches CPU to Protected Mode.
- The Kernel is Loaded.
- Reads SYSTEM.INI
- Loads Drivers.
- Graphics Subsystem is loaded (GDI.EXE and USER.EXE)
- Desktop Manager is started (PROGMAN.EXE).
- WIN.INI is read and PROGMAN.INI
Windows 95 runs in a very similar way but WIN95 only supports protected
mode and no switch exists for real mode.
Also there is a reliance on the registry.
Memory Management
First 640k is Conventional Memory
640k to 1024k is Upper Memory
Above 1024k is Extended Memory
HIMEM.SYS is loaded in CONFIG.SYS as the first driver to manage the Extended
Memory are and to convert this to XMS (Extended Memory Specification).
The first 64k of extended memory has been labelled High Memory (HMA).
DOS can be put here by putting DOS=HIGH in CONFIG.SYS.
EMM386.EXE is loaded in CONFIG.SYS after HIMEM.SYS has been successfully
loaded. This is used in the hardware reserved 384k of space in upper memory
(640k-1024k) and creates EMS(Extended Memory Specification).
Virtual Memory relies upon EMS (therefore EMM386.EXE) and uses hard disk
space as memory.
These study notes were developed by Andrew Mason.
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