Windows 7: Optimizing Performance (part 2) - Fine-Tuning Virtual Memory & Data Execution Prevention

3. Fine-Tuning Virtual Memory

Your computer uses virtual memory to extend the amount of available RAM by writing physical memory (RAM) to disks through a process called paging. With paging, Windows 7 writes a set amount of RAM, such as 1,834 MB, to the disk as a paging file, where the operating system can access it from the disk when needed in place of physical memory.

Windows 7 writes paging files to disk drives as a file named pagefile.sys. Windows 7 creates an initial paging file automatically for the drive containing the operating system. By default, other drives don’t have paging files, so you must create these paging files manually if you want to use them. However, in most instances, you won’t need to put a paging file on multiple disks, as doing so won’t necessarily boost performance.

As with many other aspects of performance, Windows 7 does a much better job than its predecessors do of automatically managing virtual memory. Typically, Windows 7 will allocate virtual memory at least as large as the total physical memory installed on the computer. This helps to ensure that paging files don’t become fragmented, which can result in poor system performance.

You can also manually manage virtual memory. If you do this, you’ll typically want to use a fixed virtual memory size. You fix the size of the virtual memory by setting the initial size and the maximum size to the same value, and this in turn prevents fragmentation of the paging file.

NOTE

In most cases, I recommend setting the total paging file size so that it’s twice the physical RAM size on the system. For instance, on a computer with 1,024 MB of RAM, you would ensure that the “Total paging file size for each drive” setting is at least 2,048 MB.

If your computer has more than 4 GB of RAM, however, you’ll probably want to set the paging file size so that it’s approximately 1.5 times the size as the physical memory. For instance, on a computer with 6,144 MB of RAM, you would ensure that the “Total paging file size for each drive” setting is at least 9,216 MB.

To achieve optimal performance, you may want to consider using a fixed minimum of 1 times the RAM and a fixed maximum of either 2 times or 1.5 times the RAM. Fixing the size of the paging file in this way ensures that Windows allocates sufficient file space to the page file initially and doesn’t need to repeatedly increase the size of the paging file as you start using programs on your computer.

You can manually configure virtual memory by completing the following steps:

1. In the Control Panel, click the System and Security category heading link.

2. Click System. In the left pane under See Also, click Performance Information and Tools.

3. Under Tasks, click “Adjust visual effects.” This opens the Performance Options dialog box.

4. On the Advanced tab, click Change to display the Virtual Memory dialog box shown in Figure 3. The following information is provided:

   Drive [Volume Label] and Paging File Size (MB)

   Show the current configuration of virtual memory. The dialog box lists each volume with its associated paging file (if any). The paging file range shows the initial and maximum size values of the related paging file.

   Paging file size for each drive

   Provides information on the currently selected drive and enables you to set its paging file size. “Space available” indicates how much space is available on the drive.

   Total paging file size for all drives

   Provides a recommended size for virtual RAM on the system and shows the amount currently allocated.

5. By default, Windows 7 manages the paging file size for all drives. If you want to configure virtual memory manually, clear the “Automatically manage paging file size for all drives” checkbox.

6. In the Drive listbox, select the disk volume you want to work with.

7. Select “Custom size” and then enter an initial size and a maximum size.

8. Click Set to save the changes.

9. Repeat steps 6–8 for each disk volume you want to configure.

10. Click OK. If prompted to overwrite an existing pagefile.sys file, click Yes.

11. If you updated the settings for a paging file that is currently in use, you’ll see a prompt explaining that you need to restart the system for the changes to take effect. Click OK.

12. Click OK twice to close the open dialog boxes. You’ll see a prompt asking if you want to restart the system. Click Restart.

Figure 3. Configuring virtual memory

You can have Windows 7 automatically manage virtual memory by following these steps:

1. In the Control Panel, click the System and Security category heading link.

2. Click System. In the left pane under See Also, click Performance Information and Tools.

3. Under Tasks, click “Adjust visual effects.” This opens the Performance Options dialog box.

4. On the Advanced tab, click Change to display the Virtual Memory dialog box shown in Figure 3-20.

5. Select the “Automatically manage paging file size for all drives” checkbox.

6. Click OK twice to close the open dialog boxes.

4. Fine-Tuning Data Execution Prevention

Data Execution Prevention (DEP) is a memory protection technology. Your computer uses DEP to mark all memory locations used by applications as nonexecutable unless the location explicitly contains executable code. If an application attempts to execute code from a memory page marked as nonexecutable, the processor can raise an exception and prevent it from executing. This behavior is designed to thwart a malicious program, such as a virus, from inserting itself into areas of memory. By allowing only specific areas of memory to run executable code, DEP protects your computer from many types of self-replicating viruses.

You can implement DEP via hardware or software. Hardware-based DEP is more robust because you can extend it to any program or service running on the computer. Software-based DEP is less robust because it typically works best when protecting Windows programs and services.

Windows 32-bit versions support DEP as implemented originally by Advanced Micro Devices Inc. (AMD) processors that provide the no-execute page-protection (NX) processor feature. Such processors support the related instructions and must be running in Physical Address Extension (PAE) mode. Windows 64-bit versions also support the NX processor feature but do not need to be running in PAE mode. And 64-bit computers natively support very large memory configurations.

You can determine whether your computer hardware supports DEP by completing the following steps:

1. In the Control Panel, click the System and Security category heading link.

2. Click System. In the left pane under See Also, click Performance Information and Tools.

3. Under Tasks, click “Adjust visual effects.” This opens the Performance Options dialog box.

4. Click the Data Execution Prevention tab. As Figure 4 shows, the lower portion of this tab lists the DEP support available.

Figure 4. Viewing your computer’s DEP configuration

Once you’ve accessed the Data Execution Prevention tab, you can configure the way DEP works using these options:

Turn on DEP for essential Windows programs and services only

Enables DEP only for the operating system services, programs, and components. This is the default and recommended option for computers that support execution protection and are configured appropriately.

Turn on DEP for all programs except those I select

Enables DEP for the operating system, as well as all programs and services you are running.

Because some programs won’t work with or will become unstable with software-based DEP, you may find that you have to add exceptions when you enable DEP for all programs. Click Add to specify programs that should run without execution protection. In this way, execution protection will work for all programs except those you have listed.