Basic Strategies for Improving Performance (part 1)

• Ensuring that you have adequate RAM

• Ensuring that you have an adequate virtual-memory configuration

• Tuning and troubleshooting SuperFetch

• Using ReadyBoost to compensate for a slow hard disk

• Managing startup programs and services

• Keeping your disks defragmented

• Maintaining adequate free space on your disks

• Avoiding tweaks of dubious value

1. Ensuring That You Have Adequate RAM

Random access memory (RAM) is the vital stuff that keeps Windows running smoothly. Having enough physical (main) memory helps reduce the operating system's dependence on virtual memory, thereby maximizing the number of times Windows is able to fetch information from fast memory chips and minimizing the number of times it has to get data from your (relatively slow) hard disk. How much memory do you need?

Microsoft's official hardware requirements for Windows 7 specify that a system must have at least 1 GB of RAM to run 32-bit Windows, and 2 GB if you plan to install 64-bit Windows. In our experience, doubling these minimums will provide a better ride for most installations.

But don't assume that more memory is always better. As it turns out, there is such a thing as too much memory, especially if you're running a 32-bit Windows version. First, there's the question of how much RAM (how many memory modules and in what sizes) your computer will physically accommodate. And then there's a hard mathematical limitation: because of the nature of address spaces, 32-bit versions of Windows can use no more than 3.5 GB of RAM, and often considerably less. The exact amount varies depending on the hardware in question; for more details see Knowledge Base article 929605, "The system memory that is reported in the System Information dialog box in Windows Vista is less than you expect if 4 GB of RAM is installed," at w7io.com/929605. (Although the title specifically refers to Windows Vista, the information applies equally to Windows 7.)

With a 64-bit version of Windows 7, this limitation on physical memory vanishes, to be replaced by limits that are defined differently for each edition of Windows. Table 1 has the details for all editions.

Memory management is confusing, perhaps more so than any other aspect of PC performance. If you scour the web for information on this topic, you will surely run into misguided advice and technical errors. Knowing the meaning of the following specialized memory-measurement terms helps you make sense of it all:

• Physical memory refers to actual RAM chips or modules, typically installed on a computer's motherboard. The amount of physical RAM available to Windows might be less than the total physical amount if another system component is using that memory for its own purposes, as is the case with "shared memory" video subsystems on portable computers. Physical memory measurements (total and in use) are reported on the Performance tab of Windows Task Manager and on the Memory tab of Resource Monitor.

• Virtual memory consists of physical memory plus the amount of space in the page file, which is stored on the hard disk. We discuss virtual memory in more detail in the next section, Section 20.3.2 on Section 20.3.2.

• Kernel memory is owned by Windows and is used to provide system services to applications. Paged memory can be backed up to the page file and replaced by application memory if necessary; nonpaged memory must remain in physical RAM at all times.

• Cached memory holds data or program code that has been fetched into memory during the current session but is no longer in use now. If necessary, the Windows memory manager will flush the contents of cached memory to make room for newly summoned data.

• Free memory represents RAM that does not contain any data or program code and is free for use immediately.

• Working Set is the term that defines the amount of memory currently in use for a process. Private Working Set is the amount of memory that is dedicated to that process and will not be given up for other programs to use; Shareable Working Set can be surrendered if physical RAM begins to run scarce. Peak Working Set is the highest value recorded for the current instance of this process.

• Commit Charge (also called commit size) is the total amount of virtual memory that a program has touched (committed) in the current session, including memory that has been paged out of physical memory to the disk-backed page file. The Memory and Physical Memory counters on Task Manager's Performance tab represent the sum of this value for all processes and the kernel. The Commit Charge Limit is the total amount of physical RAM and page file available—in other words, the maximum virtual memory.

• Hard faults are also known as page faults. Despite the negative connotation of the name, this is not an error condition. Rather, it represents an instance where a block of memory needed by the operating system or an application has to be fetched from the page file on the hard disk instead of from physical memory. A consistently high number of hard faults per second indicates a large—perhaps excessive—reliance on virtual memory, with consequent adverse performance effects.

The best way to gauge the adequacy of your currently installed RAM is to keep an eye on the Memory graph in Resource Monitor. The green portion of the bar indicates the percentage of your physical memory that's currently in use; shades of blue indicate cached memory that is available on demand (Standby). It's also important to watch the green line on the graphs to the right, which indicates the number of hard faults per second your system is generating; if you see it spike off the top of the graph for extended periods of time, you'll want to take a closer look at how memory is being used.

Pay special attention to these numbers when you're asking the most of your computer; you might even consider performing a stress test by successively opening the applications you use most often. Switch between programs, open and edit some data files, browse a couple dozen webpages, and generally try to use more system resources than you can imagine using at one time under normal circumstances. If you find yourself bumping up against the ceiling regularly, you might get a noticeable performance boost from additional RAM.

Don't get hung up on mere percentages, though. If you routinely hit a maximum of 85 percent memory usage on a machine running 64-bit Windows 7 with 6 GB of physical RAM, you have 900 MB of free RAM, which is plenty of headroom.

2. Ensuring That You Have an Adequate Virtual-Memory Configuration

Physical memory might be the vital lubricant of a happily humming Windows machine, but Windows is not designed to run on RAM chips alone, no matter how many of them you have. In addition to using physical RAM to store programs and data, Windows creates a hidden file on your primary hard disk and uses that file to manage pages of data pulled from scattered sections of the hard disk and used in physical memory when necessary. The page file acts as an extension of main memory—or, in other words, as virtual memory.

In olden days (especially in the early to mid 1990s), the memory manager's disk-backed storage was commonly called the "swap file," because its primary use was to overcome physical memory shortages. Today, the page file is an integral part of memory management, used by SuperFetch and the boot prefetcher to optimize your system for performance.

In Windows 7, Microsoft has chosen to deemphasize visible measurements of page file usage in common performance-monitoring tools. The Commit fraction in the lower right corner of Windows Task Manager's Performance tab is useful for helping you gauge the adequacy of your virtual memory setup. Note, however, that while the numerator of the fraction indicates how much virtual memory your system is currently using, the denominator reports the sum of physical memory and current page-file size.

In a default installation, Windows creates the page file in the root folder on the same drive that holds the Windows system files. The size of the page file is determined by the amount of RAM in your system. By default, the minimum size on a 32-bit (x86) system is 1.5 times the amount of physical RAM if physical RAM is less than 1 GB, and equal to the amount of physical RAM plus 300 MB if 1 GB or more is installed. The default maximum size is three times the amount of RAM, regardless of how much physical RAM is installed. On a PC with a processor that supports Physical Address Extension (PAE)—which is to say, on any PC that is capable of running Windows 7—the maximum size of the page file is 16 TB. That amount of disk space will no doubt seem horribly confining someday, perhaps even in our lifetimes, but for now it's more than enough. You can see the page file in a Windows Explorer window if you configure Windows to show hidden and system files; look for Pagefile.sys in the root of your system drive.

To see the current configuration of your system's virtual memory, open the System dialog box in Control Panel and click the Advanced tab. (For an excellent, undocumented shortcut to this dialog box, click Start, type systempropertiesadvanced with no spaces, and press Enter.) Under the Performance heading, click Settings. In the Performance Options dialog box, click the Advanced tab and (finally!) under the Virtual Memory heading, click Change. Figure 1 shows the Virtual Memory dialog box, with default settings for a machine with 2 GB of RAM (default, that is, except that we cleared the Automatically Manage Paging File Size For All Drives check box to make the rest of the dialog box easier to read).

By default, Windows creates a single page file in the root folder on the same volume that holds the Windows system files and manages its size for you. The Currently Allocated number near the bottom of the dialog box shows you how large the file is now. If conditions on your system change (you run an unusually large assortment of memory-intensive applications, for example), Windows might expand the page file. It might then return the file to its original size (or a smaller size) if the demand subsides. All this happens without intervention or notification if you leave the Automatically Manage Paging File Size For All Drives check box selected.

If you don't want Windows to do this for you, you have the following options:

• You can move the page file to a different volume if you have more than one.

• If you have more than one volume, you can establish more than one page file.

• For any page file, you can choose between System Managed Size and Custom Size.

• If you choose Custom Size, you can specify an initial size and a maximum size.

• You can remove a paging file from a volume by selecting the volume and choosing No Paging File. (You can even get rid of all paging files this way, although doing so is not recommended, even on systems with a lot of RAM.)

Should you get involved in page-file management, and, if so, how?

If you have more than one physical disk, moving the page file to a fast drive that doesn't contain your Windows system files is a good idea. Using multiple page files split over two or more physical disks is an even better idea, because your disk controller can process multiple requests to read or write data concurrently. Don't make the mistake of creating two or more page files using multiple volumes on a single physical disk, however. If you have a single hard disk that contains C, D, and E volumes, for example, and you split the page file over two or more of these, you might actually make your computer run more slowly than before. In that configuration, the heads on the physical disk have to do more work, loading pages from different portions of the same disk sequentially, rather than loading data from a single contiguous region of the hard disk.

If you are short of hard disk space, you might consider setting a smaller initial page file size. Monitor peak usage levels over time; if the peak is well below the current page file size, you can consider reducing the initial size to save disk space. On the other hand, if you're not short of disk space, there's nothing to be gained from doing this and you might occasionally overload your custom settings, thereby degrading the performance of your system.

Should you enlarge your page file? Most users won't need to do this. But you might want to keep an eye on the green line in the Memory chart on the Overview tab of Resource Monitor . If that line is spiking off the top of the graph a great deal of the time during your normal work, you might consider increasing the maximum size of your page file. (Disregard page file spikes and disk activity in general that takes place while you're not actually working. This is likely to be the result of search indexing, defragmentation, or other background processes and does not indicate a problem with your actual work performance.)

Note:

For an extremely detailed discussion of virtual memory page file management in Windows Vista, we recommend the blog post "Pushing the Limits of Windows: Virtual Memory?" by Microsoft Technical Fellow Mark Russinovich, at w7io.com/2004.