Computer Troubleshooting and Repair with Booting from CD or DVD

Why do you need booting your computer from CD or DVD?

Booting from a CD is sometimes necessary to run advanced tools like memory testing programs and password recovery tools. You'll also need to boot to a CD or DVD if you're planning to install an operating system like Windows XP or run diagnostic tools like the Windows XP Recovery Console. When you boot from a CD, what you're actually doing is running your computer with a small operating system that's installed on the CD. When you start your computer normally, you're running with the operating system installed on your hard drive - Windows, Linux, etc.

 

When do you need booting your computer from CD or DVD?

1. Your Hard Drive is corrupted and you cannot boot up through the conventional options. You usually try first more simple options of recovery like Safe Mode or Last Working Bootup Configuration. The sample of error message you might get is as follows: "Boot sector corrupt. Config.sys missing. Disk cannot be read."
2. You forgot your administrative password, and you cannot login to your locked computer a regular way.
3. Your computer is infected with virus, and you need to perform a deep Hard Drive cleaning, including the basic drivers, through external operational features.
4. You need to manipulate the Operating System drivers that constitute the core of the system, and are used by it even in the light Safe Mode. For example, you need to perform manual rebase of the basic Windows drivers to increase virtual memory interval for the high memory resources consuming software utility.
   
5. You need to perform Hard Drive imaging for backup purposes. Many utilities require booting up from the DOS or Linux external environment.

 

Time Required: Booting from a CD or DVD usually takes less than 10 to 20 minutes.

 

Here's How:

1. Change the BIOS boot order so the CD or DVD drive is listed first. Some computers are already configured this way but many are not. Usually, the key required to press, to enter BIOS, is shown on the first page. However, you need to click fast (sometimes, repeating multiple times) to ensure that your request has been processed. The key or keys combination depends on the computer model and manufacturer.
   

If the CD or DVD drive is not first in the boot order, your PC will start "normally" (i.e. boot from your hard drive) without even looking at what might be in your disc drive.

Note: After setting your optical drive as the first boot device in BIOS, your computer will check that drive for a bootable CD or DVD each time your computer starts. Leaving your PC configured this way shouldn't cause problems unless you plan on leaving a disc in the drive all the time.

2. Insert your bootable CD or bootable DVD in your disc drive.

How do you know if a CD or DVD is bootable? The easiest way to find out if a disc is bootable is to insert it in your drive and follow the remainder of these instructions. Most operating system setup CDs and DVDs are bootable, as are many advanced diagnostic tools.

Note: Programs downloadable from the Internet that are intended to be bootable discs are usually made available in ISO format.

3.    Restart your computer.

4.    Watch for a Press any key to boot from CD... message.

When booting to a Windows setup CD/DVD and many other bootable discs, you may be prompted with a message to press a key to boot to the disc. To boot to the CD or DVD, you'll need to press any key on your keyboard (like the space bar) within the few seconds that the message is on the screen.

If you do nothing, your computer will check for boot information on the next boot device in the list in BIOS which will probably be your hard drive.

Some bootable CDs and DVDs do not prompt for a key press and will start immediately.

5.    Your computer should now boot from the CD or DVD disc.

Note: What happens now depends on what the bootable disc was for. If you're booting to a Windows Vista DVD, the Windows Vista setup program will begin. If you're booting to a Slackware Live CD, the version of the Slackware Linux operating system you've included on the CD will run.

If you tried the above steps but your computer did not boot from the CD or DVD properly, check out some of the tips below.

 

Tips:

1. Recheck the boot order in BIOS. The number one reason a bootable disc won't boot is because BIOS is not configured to check the CD/DVD drive first.
2. Do you have more than one CD or DVD drive? Your computer probably only allows for one of your disc drives to be booted from. Insert the bootable CD or DVD in the other drive and restart your computer.
3. Clean the CD or DVD. If the disc is old, as are many Windows Setup CDs and DVDs by the time they're needed, clean it. A clean disc could make all the difference.
4. Burn a new CD/DVD. If the DVD or CD is one you created yourself, like from an ISO file, then burn it again. The disc may have errors on it that re-burning could correct. I've had this happen to me more than once.
5. Check CD-ROM jumpers. Not all CD-ROM drives will boot properly if the jumpers are not set properly; verify that the CD-ROM drive has the jumpers set properly. We generally recommend that you have the CD-ROM set as master on the secondary controller. This rule also applies to portable computers. 
6. Check if your CD-ROM is operational. Verify other CD discs work in the CD drive. If the drive is a bad drive it will be unable to boot from the CD disc because it cannot read from the disc.

 

Types of Bootable CDs and DVDs:

There are multiple bootable CDs and DVDs, starting from the Operation System CD you received with the computer purchase. Aftermarket offers multiple disks configurations, as legal, based on the free operating systems, as not very legal, like portable Windows compilations. We will review some of the options in the following articles of this chapter.

 

 

Additional Information:

http://pcsupport.about.com/od/tipstricks/ht/bootcddvd.htm

http://www.computerhope.com/issues/ch000217.htm

http://techpaul.wordpress.com/2007/08/03/how-to-boot-from-a-cd/

http://www.pcrepairs-online.com/How_to_Boot_From_CD-DVD_Drive.htm

 

Virtual Memory Optimization in Windows Computers

What is Page File?

A key to improving your PC’s performance is the page file (also called the swap file and/or virtual memory). A page file is a cache of data on your hard drive; this cache is used to supplement your computer’s main memory (RAM). When a computer runs out of memory, it uses the page file. Since data access on a hard drive is slow compared to accessing memory, your PC’s performance takes a hit.

What is exactly Virtual Memory?

In a 32-bit computer, the memory addresses are 32 bits long and stored as binary (base 2) numbers. There are approximately 4 billion possible different 32-bit binary numbers (2^32=4,294,967,296). Because of this, there is a 4GB limit for addressable memory in a 32-bit computer.

A program instruction on an Intel 386 or later CPU can address up to 4GB of memory, using its full 32 bits. Each process is assigned an address space of 4GB of virtual memory, regardless of the amount of available physical memory. Each process is isolated from the rest and has its own 4GB address space. This means that the 4GB addressability limit applies on a per-application basis, not across all applications taken together.

This is normally far more than the RAM of the machine. The amount of physical memory on the computer is not related to the amount of memory address space. If a computer has 256MB of physical memory, there is still a 4GB memory address space, and if a computer has 8GB of physical memory, there is still a 4GB memory address space.

Applications are not allowed direct access to physical memory. When an application requests more memory, Windows maps some physical memory (as long as some is available) into the process’s address space.

The hardware provides for programs to operate in terms of as much as they wish of this full 4GB space as Virtual Memory, those parts of the program and data which are currently active being loaded into Physical Random Access Memory (RAM). Windows maintains several tables that keep track of all of this, and the application knows only about the virtual memory address.

The processor itself then translates (‘maps’) the virtual addresses from an instruction into the correct physical equivalents, doing this on the fly as the instruction is executed. The processor manages the mapping in terms of pages of 4KB each - a size that has implications for managing virtual memory by the system.

Why do I need page file optimization?

Optimizing your page file when you’re running low on RAM is always a good idea. When all physical RAM in a computer is in use, Windows starts using the hard disk as if it were additional RAM. This is why we have a Page file (also called the swap file). Because RAM memory is a lot faster than the hard disk, whenever the computer begins to use the Page file to relieve memory pressure, we begin to experience drastic performance degradation.

One of the most effective things you can do to improve performance is ensure that there is enough RAM available to avoid frequent paging (swapping) of memory contents between disk and RAM.

This means that the actual limit on the memory used by all applications is the amount of RAM installed plus the maximum size of the Page file.

How much swap space do you need? That depends the amount of RAM you have and the programs you use. The current algorithm Windows uses to set the default paging file size is:

• If total physical RAM is less than 2 gigabytes (GB), the paging file is set to 1.5 times the amount of RAM or 2 GB, whichever is smaller.
  
• If total physical RAM is equal to or more than 2 GB, the default size is set to 2 GB.

Note that in Default Windows settings the setup amounts of initial and maximum page files are different. It is recommended to make its initial size as big as the maximum size. Although this will cause the Page file to occupy more HD space, we do not want it to start off small, then having to constantly grow on the HD. Writing large files (and the Page file is indeed large) to the HD will cause a lot of disk activity that will cause performance degradation. Also, since the Page file only grows in increments, you will probably cause Page file fragmentation, adding more overhead to the already stressed HD.

Should You Disable Your Page File?

Several experts suggest that you disable the page file to increase performance, by doing away with the page file that means your computer won’t have to access the hard drive. So it should be faster, right? It can be, or it can cause several instability problems for your computer. Many programs won’t even run without a page file enabled. The effect definitely depends on the amount of physical memory available. The 8 GB RAM systems might run just like normal, but when you lower the amount of memory available to 2 GB, system instability will definitely be visible.

Page File configuration

For simplicity of the task, you might follow the Microsoft recommendations listed above for the amount of the Page file settings. However, you can go further and set it according to particular needs of your computer, which require more time and more experience.

Open System Properties, then the Advanced tab and press the Performance Settings button, selecting the Advanced tab, finally pressing the Change button. Select the Drive which XP is installed to and set the Paging file size for selected drive to Custom size, setting the Initial size and Maximum to 1500MB according to the basic recommendations. If you have multiple drives available ensure these are set to No paging file. Click Ok and restart as required for the changes to take effect.

You can stop right here if you do not want to go deeper and you are satisfied with standard settings. Otherwise, you can continue with recommendations below.

After computer reboot press Ctrl + Alt +Delete simultaneously and load the Task Manager, selecting the Performance tab. This tab allows use to monitor peak Virtual Memory use (The Peak value in the Commit Charge (K) section). This window can be minimized and you should then run your most resource intensive Applications in order to see just how Virtual Memory is utilized. Once you’re satisfied with your testing switch back to Task Manager.

The Peak value records maximum Virtual Memory use during the session, in K, e.g. in the image above 324548K. Dividing this amount by 1024 gives you the value in MB - 317MB in this instance. For improved stability this value should be padded, so add at least 50MB to this value, e.g. 317MB should be increased to 400MB. This provides us with a Minimum Page File size to use. If the real demand of virtual memory is different, you can tweak the original settings.

Once more open System Properties, select the Advanced tab and press the Performance Settings button, selecting the Advanced tab, finally pressing the Change button.

A few general points to recall before you do anything;
If you have only 1 Hard Drive, split into multiple partitions, the Page File should be set to the partition XP is installed to, you should not create multiple Page Files for different partitions in this case, i.e. 1 Hard Drive = 1 Page File.

If you have multiple Hard Drives installed it is beneficial to locate the Page File on the Hard Drive XP is not installed to; but only where the other Hard Drive is of a similar or better performance, e.g. if you have a SATA Drive and ATA 100 Drive the Page File should be located on the SATA Drive regardless as it is notably faster.

The Page File should not be located on a mirrored Drive, e.g. RAID array, if possible as fault tolerance/backup is not required and may decrease performance.

How to overcome the 4GB limitation for page file in Windows?

When you set the paging file size in Windows, the documentation states that the largest paging file that you can select is 4,095 megabytes (MB). This limit is imposed by the page mapping that we use on x86 processors. These processors cannot handle more pages per page file. This is the limit set per volume; you can actually create paging files this large on one or more drives if you need a larger paging file. If extra drives or volumes are not available, you can create multiple paging files on a single drive by placing them in separate folders.

To create multiple paging files on one volume to overcome the 4,095-MB limit:
1. On the drive or volume you want to hold the paging files, create folders for the number of paging files you want to create on the volume. For example, C:’Pagefile1, C:’Pagefile2, and C:’Pagefile3.
2. Click Start, Click Run, type regedit in the Open box, and then click OK.
3. In the left pane, locate and click the following registry subkey:
HKEY_LOCAL_MACHINE’System’CurrentControlSet’Control’SessionManager’MemoryManagement
4. Find the Pagingfiles value, and then double-click it to open it.
5. Remove any existing values, and add the following values:
c:’pagefile1’pagefile.sys 3000 4000 c:’pagefile2’pagefile.sys 3000 4000 c:’pagefile3’Pagefile.sys 3000 4000
6. Click OK, and then quit Registry Editor.
7. Restart the computer to cause the changes to take effect.
8. Access the virtual memory settings to check the properties of the paging file. To do this, follow these steps.

Sources and Additional Information:
http://www.petri.co.il/pagefile_optimization.htm
http://g4tv.com/techtvvault/features/36099/Optimize-Windows-XP-Page-File.html
http://support.microsoft.com/kb/237740
http://www.pctipsbox.com/speed-up-windows-by-optimizing-your-page-file/
http://www.techspot.com/tweaks/memory-winxp/memory-4.shtml