Computer architecture

A+ Guide to Managing and maintaining Your PC - Forth Ediition, Andrews, Jean

Chapter2 - How Hardware and Software Work Together

1. Hardware and Software Interaction: An Overview
   1. Hardware is like an automobile, it is useless with out somone behind the wheel
   2. Software is like the Chauffeur who takes instructions from another source and tells the hardware what to do
   3. The software has different levels
      1. Application software - various programs that people use
      2. Operating system - Works with the applications software on one side and the hardware on the other side
      3. Various OS have been available over the years and currently
         1. DOS - first OS for IBM/Compatable computers
            1. Wrtitten for Early PCs - verry limited
            2. Even though Win 3.x appeared to be an OS it was not, it was a shell for DOS
         2. Windows 9X (95, 98, ME)
            1. True OS but had DOS core for compatability
            2. Popular with home and business users alike
         3. Windows NT, 2000, XP
            1. Break from DOS compatabilites.
            2. In general come in Server and Client (sometimes called PRO) versions
         4. Unix - OS for networks and Internet use
         5. Linux - scalled down linux - open source
         6. OS/2 - IBM attempt at GUI
         7. MAC OS - For Macintosh computes
2. System Resources
   1. The 8-bit and 16-bit ISA Slots
      1. The bus that was used on the first PC systems was called the ISA
      2. It used an 8 bit data bus
      3. Other lines are used for voltages, addresses, interupt requests, and other stuff
      4. Later a 16 bit slot was created and called Extended Industry Standard Archtecture (EISA)
      5. ISA slots, though still used, are slower than other I/O slots
      6. The cards themselves usually had jumpers or switches on them to determine what IRQ and addresses used.
   2. Interrurpt Request Numbers (IRQ)
      1. When a piece of euqipment needs to do something it places a voltage on its interupt request line (IRQ) to flag that it needs attention
      2. Each device gets its own IRQ number and this is how the computer is able to tell which device needs attention.
      3. IRQ 0 (system timer) and IRQ 1 (Keyboard) are not available for other devices
      4. This left 2 through 7 for other things, but they had specific things that they were assigned to
      5. IQO 2 had been reserved for a connection to mainframes by IBM
      6. With only 5 IRQs free we need a new way to connect more than 5 devices, especially with the EISA
      7. The plan was to use IRQ 2 to signal to another controller but other uses had been created for it by some manufacturers.
      8. A New IRQ (9) was created and tied to IRQ2 so that both could be used.
      9. To see how your IRQs are assigned you can use MSD in DOS or Device Manager with WIn 9x and above
      10. Another way to service the needs of the computer components, is to do polling
      11. With polling software is always running to check on various devices attached to the equipment
   3. Memory Addresses
      1. The way that memory is accsed is by addresses that get assigned when the operating system loads
      2. The CPU uses an address bus to communicate the memory location that it needs to reference.
      3. Because only 20 address lines were available in original computers that limited memory to 1,024KBytes of memory (1 Meg)
      4. DOS used only the first 640 K of that 1 Meg. The rest of that memory was reserved for devices. All that was above 1 MEG became extended memory that could only be used under special circumstances
      5. Windows does not break this memory up, all memory is available to the Operating System and the Programs. Windows 9x does have some memory fall backs to DOS though
      6. Shadowing ROM
         1. Sometimes ROM BIOS will be copied into RAM memory because it can be accessed faster
         2. Access will be the same either way. Just faster this way
   4. I/O Addresses
      1. Another way of addressing devices is by the I/O addresses assgined to them.
      2. The address match one for one the same lines as the IRQ numbers
   5. DMA Channels
      1. Direct Memory Access is used to bypass information from having to go to the CPU first
      2. 0, 1, 2, and 3 are used for 8 bit, 4, 5, 6, and 7 are used as well for 16 bit.
      3. Not all devices would be using this. Disk drives are a common use.
3. How an OS relates to Other Software
   1. Real (16 Bit) and Protected (32-Bit) Operating Modes
      1. Real Mode assumes that there is only one program running at a time. This is called single tasking.
      2. Because of this applications are given direct access to the memory
      3. In Protected Mode more than one program can run at a time. This is called multitasking.
      4. Each program will be assigned its range of memory to be used. Hence it is protected from other aplications
      5. In protected mode virtual memory (Hard Drive space being used as RAM) can be accessed by the Operating System
      6. Computers start in real mode and must be made to switch to protected mode.
      7. In protected mode time is given to one task and then jumps to another task, stoping the first task temporarily. This is called preemptive multitasking.
      8. How an OS Uses Real and Protected Modes
         1. Programs must be written to run in real or protected mode. Some are even written to be aware that they are in protected and run sort of as a hybrid.
         2. Windows 3.x was not an operating system as such but an operating enviornment. It provides support to the applications.
         3. 16-Bit and 32-Bit Software
            1. Software written for WIndows 3.x is 16-bit software
            2. It is designed to be watching other applications and not infringe on them.
            3. Windows 9x is a hybrid, designed to use both of them
            4. Windows NT and above are strictly 32-bit software
   2. How an Os Uses BIOS and Device Drivers
      1. How an OS Uses System BIOS
         1. System BIOS contains information about how to run simple hardware common to all equipment
         2. Things like keyboard, hard drive, floppy drives
         3. BIOS is configured from the set up program that can be accessed when the computer starts
      2. How Device Drivers Control Hardware
         1. Hardware uses special software (device drivers) to make it available to the operating system
         2. These are special written for the operating system and the hardware
         3. Device Drivers Under Windows 9x
            1. Windows 9x is designed to use 32 bit drivers whenever available
            2. To provide backward compatability to DOS Windows 3.x 16-bit drivers can be loaded in config.sys, autoexec.bat and system.ini
            3. Windows 9x keeps information about 32 bit drivers in the registry
            4. Whenever posible you should try to use the most recent drivers to patch problem that may have come up earlier
            5. Running 16-bit drivers under 9x can cause the system to run slow (as well as other problems)
            6. Look for 16-bit drivers to be loaded from the three files mentioned above as well as seeing them as problems indicated in Device Manger
         4. Device Drivers Under Windows 2000
            1. 2000/xp will load 16 bit mode drivers but there is no guarentee that they will work.
            2. Always check the Hardware Compatability List (HCL) to verify if drivers are designed for your OS
4. How an OS launches an aplication
   1. Loading Application Software Using the Windows Desktop
      1. When installed Windows offers several ways for software to be run
         1. From a shortcut on the desktop
         2. From the start menu choose programs and the look for the installed program shortcut
         3. From the RUN command and enter the command line to start it
         4. Find the program in My COmputer or Windows Explorer and run it from there.
5. Chapter Summery
6. Key Terms
7. Review Questions
8. Hands-on Projects