Read this whole guide offline with no ads, for a very low price!
Click Here!

Custom Search







Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 8: Motherboards

Previous Topic/Section
Memory Addresses
Previous Page
Pages in Current Topic/Section
1
Next Page
Logical Names
Next Topic/Section

Memory Mapping

Memory mapping is the process of reserving blocks of memory in the system. Memory addresses are typically expressed in hexadecimal notations. A partial list of memory addresses might look like this:

00000 unused

00001 unused

00002 unused

00003 unused

00009 unused

0000A unused

0000B unused

0000C unused

FFFFF unused

In this particular example, we are memory mapping the I/O. It is important to note that I/O is not stored in RAM, but in different areas of the system memory, such as ROM chips on an expansion card. By assigning a particular memory map to a communications port, when the CPU is ready, it knows where to find the data (the In part of I/O). When the CPU needs to send data out, it uses this address again. This process is known as I/O Addressing.

A typical example is communication port 1. The standard memory address for Com1 is 3F8h.

While a sound card needs an I/O address, since it really is several devices on one card, the I/O address needs can (and do) vary. The challenge arrives with the fact that when I/O addresses are specified, the only part specified is the beginning of the I/O address. A device may only need as little as one byte, or as much as 64 bytes.

It would seem with 32, 64, or even 256 MB of ram, there is plenty of room to find an address. In addition, there is, however we have one little issue that shoots a hole in that logic. That would be the need for backward compatibility. Prior to Windows 95, finding I/O overlap was difficult. The routine known as Device Manager in the Control Panel->System of Windows 95 made this a much simpler process to discover I/O overlap.

I/O Addresses Are Different

I/O addresses are not exactly like IRQ and DMA. IRQ and DMA are typically assigned one per device and are of uniform size.



Previous Topic/Section
Memory Addresses
Previous Page
Pages in Current Topic/Section
1
Next Page
Logical Names
Next Topic/Section

If you find CertiGuide.com useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider buying an inexpensive PDF equivalent of the CertiGuide to A+ (A+ 4 Real) from StudyExam4Less.com. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

CertiGuide to A+ (A+ 4 Real) (http://www.CertiGuide.com/apfr/) on CertiGuide.com
Version 1.0 - Version Date: March 29, 2005

Adapted with permission from a work created by Tcat Houser et al.
CertiGuide.com Version Copyright 2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.