Review's Answers

Why does a computer need an expansion bus?

Expansion slots on the motherboard are standardized connections that allow the installation of any device not soldered to the motherboard. By providing this connection to the expansion bus, computers can be customized to meet the requirements of the user.

Name the available expansion buses.

The available expansion buses are: ISA, MCA, EISA, VESA, AGP, and PCI.

What happens if two non-PCI devices use the same I/O address?

The computer will lock up.

How many IRQs are available on most PCs?

There are 15 IRQs available, although some of them are permanently assigned.

Under what conditions would a second modem-installed and assigned to COM3-not work?

If the first modem had been using COM1, the failure would be the result of an IRQ conflict. Devices assigned to COM1 and COM3 both make use of IRQ4. If the first modem has already been assigned to COM1, a conflict will occur when both modems make use of IRQ4.
One solution is to assign COM3 an available interrupt such as IRQ10.

Identify the two divisions of the external data bus and describe the purpose of each.

The two divisions of the external data bus are the system bus and the expansion bus. The system bus supports the CPU, RAM, and other motherboard components. The system bus runs at speeds that support the CPU.
The expansion bus supports any add-on devices via the expansion slots and runs at a steady 7.16 MHz.

What is the standard that governs computer buses?

IBM established the ISA industry standard, thus generating the market for clones. The term ISA (Industry Standard Architecture) did not become official until 1990.

What is the difference between ISA and EISA cards?

EISA uses a double slot connector that is compatible with ISA devices. Physically, the EISA bus is the same size and looks similar to the ISA. However, they differ in the number of contacts and the depth of the slot. On close inspection, you can see a double set of contacts (one above the other).

Why was VESA created?

The Video Electronics Standards Association (VESA) is a trade association of display-adapter vendors. It was created to address the need for faster video to support the increased demands of new graphical operating systems like Windows and OS/2. These environments called for far better graphics and color management than the older character-based operating systems like CP/M.

What is bus mastering?

Bus mastering allows a device to gain control of the bus to perform special tasks without processor intervention.

Describe ways in which the PCI bus is better than previous technologies.

The PCI (Peripheral Component Interconnect) bus was designed by Intel to be a stronger, more flexible alternative to the current expansion buses while maintaining backward compatibility. It is independent of the CPU, so it is better than the VL bus and is not limited to use in 486-based computers.

How does the CPU use I/O addresses?

The CPU uses the unique address (actually a block of addresses) to communicate with a device in the system using the bus.

What is the I/O port address of COM2?

The I/O port address of COM2 is 2F8.

What are the functions of IRQs?

An IRQ is used by a device to send a request to the CPU for permission to transmit data so that all devices do not attempt to communicate at the same time.

List as many of the standard IRQ assignments as you can.

Here is a list of IRQ assignments. How many did you get?

What is the function of the DMA chip?

The only function of the DMA chip (8237) is to move data. It handles all data passing from peripherals to RAM and vice versa.

Why is it important not to assign an IRQ to more than one device?

If two devices have the same IRQ and try to communicate with the CPU at the same time, the resulting conflict will lock up the computer.

What is the difference between COM ports and LPT ports?

COM ports are for serial communications, and LPT ports are parallel ports normally used with printers.

Why is it important to document IRQs, DMAs, and I/O addresses?

Because these three things cause more conflicts than perhaps anything else in a computer, you will be able to reduce installation times and correct conflicts.