Guidelines for Designing Flash-Based Ultra Low Cost PCs for Windows XP. April 3, 2008

Transcription

1 Guidelines for Designing Flash-Based Ultra Low Cost PCs for Windows XP April 3, 2008

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3 CONTENTS Introduction... 3 What are Flash-based Ultra Low Cost PCs?... 3 Design Considerations... 3 Hardware Considerations... 4 CPU... 4 Flash Storage Devices... 4 Read and Write Speeds... 4 Capacity... 5 Lifetime... 7 Containment in ULCPC Case... 8 Storage Interfaces... 8 RAM... 9 Windows XP Performance... 9 Page File... 9 Crash Dump File Hibernation File Summary of Design Considerations Additional Resources

4 Introduction This document provides general recommendations to help you design flashbased ultra low cost PCs (referred to as ULCPC through the rest of this document) that are intended to run the 32-bit version of the Windows XP operating system. Computer system designers can use this document to build ULCPC platforms that can ease the Windows XP deployment process and reduce delivery time of ULCPCs to customers. If you choose to follow these recommendations, you might reduce the development cost of device drivers, reduce the design time, and optimize the Microsoft Windows operating system experience on the ULCPC. You can also use ready-made system components to build ULCPCs without developing system designs or drivers, and instead leverage Windows XP technology to support the hardware. Please note these recommendations are subject to change. There may also be additional licensing and/or hardware requirements that apply to Windows XP deployments on a flash-based ULCPC, therefore please contact Microsoft for further information. Any additional hardware and other requirements will be outlined in a separate License Agreement. What are Flash-based Ultra Low Cost PCs? Flash-based ultra low cost PC is a personal computer that: Has a 2 through 8 gigabyte (GB) flash storage device instead of a conventional rotating hard disk drive for the system volume. Encompasses affordability, small form factor, and low power consumption in the design to provide a good user experience and a full day of work on a single battery charge. Withstands the heat, dust, humidity, and unreliable power that can impact its performance. Provides an affordable computing solution. Design Considerations This section includes recommendations and best practices to consider in your design planning for a ULCPC that will run Windows XP. In the following sections, you will find the hardware recommendations and how they can affect Windows XP performance. These design considerations can help you understand and determine which tradeoffs you can make between hardware and Windows XP performance. 3

5 Hardware Considerations This section contains system recommendations based on benchmarking of ULCPCs that were running the 32-bit version of Windows XP. These recommendations reflect the best price/performance ratio that could be achieved by finding a balance between the CPU, RAM, and flash storage device at the time this document was written. Before following the recommendations outlined in this section, contact Microsoft to find out if additional licensing or hardware requirements apply to Windows XP deployment on a flash-based ULCPC.For general Windows XP system requirements and recommendations, see: CPU We recommend a minimum CPU speed of 500 megahertz (MHz) and an optimal CPU speed of 1 GHz. Choosing a CPU with a higher speed can further improve performance. The CPU speed that you choose should depend on the user scenario, which includes the applications you decide to deploy with Windows XP. Note that the minimum CPU speed of 500 MHz is higher than that required by the Windows XP system requirements. Flash Storage Devices Recent flash technology advances and reduction in prices for flash storage are making flash storage devices an increasingly attractive alternative to traditional hard disk drives. The main advantages of flash storage devices include: Reliability. No mechanical moving parts that can break on impact or wear out. Less susceptible to environmental conditions like heat, dust, and humidity. Power consumption. Flash storage device uses less power than traditional hard disk drives. Form Factor. Smaller size enables smaller form factors. Cost. The minimum cost threshold of a hard disk drive will be greater than that of a flash storage device because the flash storage device has no mechanical components. Because Windows XP was designed for installation on a traditional hard disk drive, using a flash storage device presents some challenges. Suggestions on handling those challenges are discussed in the following sections. Read and Write Speeds The recommended random I/O write and read speeds for storage devices are 5 megabytes (MB) per second or higher. Choosing a flash storage device with read speeds below 5 MB per second can affect the start time of Windows XP and its overall performance. Flash storage devices with a read speed of 5 MB per second or less can 4

6 take up to 10 times longer to start up as flash storage devices with a read speed of 10 MB per second. You should consider the user scenario when determining the appropriate random I/O read and write speeds for the flash storage device that you choose. Most flash storage devices are rated for sequential I/O speeds. Contact the flash storage device manufacturer to determine the random I/O speed of the storage device you plan to use. Volume Compression Volume compression affects the system volume in the following ways: Increases CPU usage. When the system volume is compressed, Windows XP compresses and decompresses all data read and written respectively to the flash storage device. Compression and decompression require that the CPU process the data. This increases the CPU usage by 1 to 5 percent. Increases size of write requests to the flash storage device. When you compress a volume, the size of write requests increases because the amount of data written to and read from the volume increases. This is caused by the compression, decompression, and extraction of data written to and read from the flash storage device. On average, compression will increase the number of write requests to the flash storage device by 25 percent. Because the total size of Windows XP before installing Windows updates, applications and add-ins is 1.1 GB on the system volume, we recommend compressing the volume for 2 GB flash storage devices. Because compression increases CPU usage and the size of write requests to the flash storage device, we recommend that you investigate how typical use under a specified user scenario will impact Windows XP performance. Capacity Windows XP was designed for systems with hard disk drives that are 10 GB or larger, but ULCPCs contain flash storage devices that have a capacity from 2 GB through 8 GB. You can use the following guidelines to help you choose the right flash storage device capacity based on the specified user scenario. First, you should consider how much space you need for Windows XP on the flash storage device. Consider the size of following items to determine the appropriate capacity: Windows XP footprint. The base size of Windows XP with Service Pack 2 (SP2) integrated should be approximately 1 GB. This doesn t include Windows Internet Explorer 7 updates or Microsoft Windows Media Player 10 updates. Windows XP add-ins and feature files. You should include the following addins in the Windows XP deployment: Multilingual User Interface Packs (MUIs) and Language Interface Packs (LIPs), as applicable. You can also enable the following features in your Windows XP deployment: the page file, crash dump file, and hibernation file.( For more information on how capacity can be impacted by the page file, hibernation file, and crash dump file, see the Windows XP Performance later in this document.) Windows XP updates. The average size of Windows XP updates that will need to be installed during the ULCPC lifetime depends on whether you delete the temporary files that Windows XP updates create. If you delete all temporary files that Windows XP updates create, the updates will be approximately 165 MB a year. If you do not delete all the temporary files, the updates will be 5

7 approximately 250 MB a year. These estimated values were calculated using the average number of updates since Windows XP RTM through the release of Windows XP SP2. The size of Windows XP updates for Service Pack 3 (SP3) might be larger. Additional files generated during Windows XP run time. These are additional files that Windows XP generates at run time, such as log and temporary files. The following formula can help you determine how much space Windows XP will need on the flash storage device: WINXP_SIZE = A+B+((C+D)*L) Where: A = Windows XP footprint (MB) B = Windows XP add-ins and feature files (MB) C = Windows XP updates (MB/year) D = Additional files generated during Windows run time (MB/year) L = Anticipated ULCPC lifetime (years) Next, you should consider how much space is needed by any additional applications that you want to install on the flash storage device. Consider the size of following items to determine the appropriate capacity: Base size of application. This is the size of the installation files. Application add-ins and feature files. These are the add-ins that you must include in the installation. These vary depending on the application. Application updates. This is the average size of application updates that must be installed during the ULCPC lifetime. The following formula can help you determine how much space your applications will need on the flash storage device: APPS_SIZE = A + B + (C*L) Where: A = Base size of application (MB) B = Application add-ins and feature files(mb) C = Application updates (MB/year) L = Anticipated ULCPC lifetime (years) Finally, you should estimate the amount of data that users will have for their personal files on the ULCPC. Even though this depends on each user scenario, we suggest that you allocate at least 200 MB for personal files per every 2 MB of storage. You should also consider that your users may increase the quantity of personal files they save on the ULCPC as their computer experience grows. The following formula can help you determine how much space the user will need to save personal files on the ULCPC: USER_DATA = A * L Where: 6

8 A = Anticipated storage required for user data (MB/year) L= Anticipated ULCPC lifetime (years) The flash storage capacity will be the sum of the values you calculated above, as represented by the following formula: Flash Storage Capacity = WINXP_SIZE + APPS_SIZE + USER_DATA Although we strongly recommend that you use these equations to determine the flash storage device capacity for each user scenario, you should allocate at least as much free space as the total space occupied by Windows XP and applications. For more information on how the page file, hibernation file, and crash dump file impact the flash storage device, see the Windows XP Performance section later in this document. Lifetime Defining the lifetime of the flash storage device can help you determine its appropriate capacity. The flash storage device lifetime is the number of years it takes for the flash storage device to fail under the defined user scenario. The following factors affect the flash storage device lifetime: Capacity. Under the same user scenario, flash storage devices with greater capacity tend to have a longer lifetime than smaller capacity flash storage devices. Controller efficiency. The controller manages data mapping, erase cycles, error correction, and bad blocks. The controller s efficiency in carrying out these functions contributes to the lifetime of the flash storage device. Efficiency can vary between controllers because the controller s functions can be implemented differently. A more efficient controller should extend the flash storage device lifetime when compared to a less efficient controller. Erase cycles. If a block in the flash storage device reaches the maximum number of erase cycles, this block could start failing. For example, assume we have a flash storage device that has a capacity of 1 MB and supports 10,000 erase cycles. This device can theoretically have 10,000 MB of data written to and erased from the device before the blocks fail. Note that in this example, the 10,000 MB of data is not a measure of the device s capacity, but the total number of write requests and erase requests that occur on the flash storage device before failure. You can use the following formula to help you determine the lifetime of the flash storage device: Lifetime (years) = Storage write capability (MB) / Write rate (MB/Year) The following list explains the values in the formula: Storage write capability (in MB). The storage write capability is the total estimated number of write requests that can be performed before the storage device will fail. The storage write capability includes all write requests (for example, the user, Windows XP, applications, and hardware components) performed on the flash storage device for the defined user scenario. When you determine the write capability, you should consider the existing data on the flash storage device. Taking this into account will help improve the accuracy of 7

9 the write capability because the existing data can affect the controller efficiency. You can use the following formula to help you determine the storage write capability: Storage write capability (MB) = Capacity x Controller efficiency x Erase cycles This is a simplified calculation for storage write capability, and a better calculation might require help from a flash storage device manufacturer. Write rate (in MB/year). The write rate is the average number of write requests to the flash storage device per year for the specified user scenario. The write rate includes the total number of write requests that the user, Windows XP, applications, and hardware components perform on the flash storage device during normal use for the defined user scenario. The number of write operations over the lifetime of a flash storage device is inversely proportional to the length of the storage device lifetime. For example, the lifetime of a flash storage device for an Internet-only user scenario is going to be longer than a programmer user scenario because the Internet user is going to have fewer write operations than a programmer. To determine the write rate, you can set up a ULCPC that includes Windows XP, drivers, and applications specified by the user scenario. You can then use a tool such as the Performance Monitor (also known as PerfMon ) to monitor all write requests to the flash storage device over a given period of time. The write requests done on a computer for a given period of time can then be calculated and extrapolated to give you the write rate over a year. For more information on how the flash storage device lifetime can be impacted by the page file, hibernation file, and crash dump file, see the Windows Performance section later in this document. Containment in ULCPC Case The flash storage device should be contained inside the ULCPC case. This is required because a license for Windows XP is valid only when it is installed on an internally mounted non-removable storage device. You may also consider putting the flash storage device in a connector socket so that technicians can easily replace the flash storage device when it fails. This will also help in a user scenario that requires extending the ULCPC lifetime. Storage Interfaces Although there are many different types of storage interfaces, implementing some of them using Windows XP may require custom designs and drivers, which can extend ULCPC design and development time, impact system support, and reduce application compatibility. We recommend Advanced Technology Attachment (ATA) because it is natively supported in Windows XP. ATA is completely transparent to the Windows XP operating system, does not impact application and tool compatibility, and can reduce ULCPC design and development time. All parallel ATA (PATA) or serial ATA (SATA) interfaces are supported in Windows XP. Although we recommend you use ATA, Windows XP also supports Universal Serial Bus (USB) and Secure Digital (SD) interfaces. 8

10 You can learn more about the advantages of using ATA as the interface in the Windows XP Performance section later in this document. All interface types should integrate into the Windows storage path below the disk.sys or disk.sys equivalent driver. This will guarantee that these devices are recognized as disk objects. Disk objects are fully supported by the upper layers in the storage driver stack, and do not require any additional changes to the volume/partition manager, file system, I/O manager layer, and applications. RAM We recommend a minimum of 256 MB and optimum of 512 MHz of RAM to run Windows XP and additional applications on an ULCPC. Choosing to preinstall more RAM can further improve performance. Running newer applications and loading multiple applications and their DLLs simultaneously may require more RAM. For more information on how the page file can impact the RAM, see the following Windows Run time section. Windows XP Performance The following sections on page file, crash dump file, and hibernation file discuss how enabling these files may affect the Windows XP performance and hardware components. Before following the recommendations outlined in this section, contact Microsoft for further information to find out if additional licensing or hardware requirements apply to Windows XP deployment on a flash-based ULCPC. Page File Both the RAM and the page file determine the size of the virtual memory that Windows XP uses. You must consider the impact that the page file has on the RAM and the space that is allocated on the flash storage device by the page file. Page file is only supported in Windows XP when you choose to use ATA or SD as your interface type. If you choose to use a USB interface, page file is not supported. If the page file is enabled, it can potentially double the number of write requests to the flash storage device, which may reduce the lifetime of the flash storage device in half. By default, the minimum size of the page file is 1.5 times the size of RAM and the maximum size of the page file is 3 times the size of RAM. To set the minimum and maximum page file to a fixed size that is smaller than the default page file sizes, you need to define application scenarios in your user scenario. The application scenarios will define which programs users might use at the same time. For example, one application scenario could include users concurrently running Windows Internet Explorer and Microsoft Word. To calculate the minimum and maximum page file sizes, you must determine the working set for each individual application. The working set is the amount of virtual memory that is used by an application, including the application itself, its application-specific data, DLLs, and user data. For each application scenario, find the sum of the individual application working sets. The application scenario with the largest working set is the minimum value for the page file size. For the maximum value for the page file size, multiply the largest working set by two. Your user scenario can help you decide if you should increase the amount of RAM or create a page file to increase the size of virtual memory. If your minimum page file size is small, you may consider increasing the amount of RAM. You will need to work any virtual memory modifications that may impact the flash storage device into your 9

11 calculation in determining capacity. For more information, see the Capacity section in this document. If you choose to have a page file, we recommend limiting the size of the page file to 1.5 times the size of RAM. Keep in mind that for a 2 GB flash storage device, the operating system with all its files should occupy more than half of the storage space. If you choose to disable the page file, the size of the virtual memory is the same as the size of RAM. In this case, if an application attempts to allocate virtual memory and the amount of virtual memory is insufficient, the allocation will fail. If the amount of available virtual memory reaches roughly 20% of the total virtual memory (or in this case, the same as the size of RAM), Windows XP will display a low virtual memory notification, and starting additional applications or allocating virtual memory for already running application may fail. To compensate for the limited virtual memory size, you can increase the amount of RAM in the ULCPC. We recommend disabling page file for a 2 GB flash storage device because of the potential impact that the page file has on the flash storage device lifetime, and the reduced free space for additional applications and user data on the flash storage device. Crash Dump File A crash dump file is generated when a failure occurs in the kernel, which includes the Windows XP subsystems and drivers. The crash dump file helps you analyze the cause of the failure. If page file is disabled, a crash dump file is not supported because the parts in the kernel and storage drivers related to crash dump recovery use the page file to write the contents of the failure. If page file is enabled and Windows XP is in an unknown state, a file for saving crash dump data can't be created and the data is saved instead to page file. If you plan to enable the crash dump file, remember that the crash dump file is only supported in Windows XP when you use ATA as your interface type. You should work this back into your calculation in determining the capacity for the flash storage device. For more information, see the Capacity section in this document. If you use USB or SD as your interface type, the crash dump file can t be created, and requires you to manually analyze computer failures that occur. The crash dump file will vary in size from 64 KB through the size of the RAM in the ULCPC. To determine the average size of the crash dump files, you can run tests for the user scenario on the ULCPC. Because we recommend that you disable page file for ULCPCs that use 2 GB flash storage device, the crash dump file will not be supported. You may want to enable the crash dump file for flash storage devices with capacities that are greater than 2MB, but you must use the ATA interface type and enable page file. Hibernation File A hibernation file is used to save the operating system state while a computer is in the S4 power state. The hibernation file is used to resume operation from the time that Windows XP went into hibernation mode. A hibernation file is only supported in Windows XP when you use ATA as your interface type. If you plan to enable hibernation files, you will need to work this back into your calculation in determining the capacity for the flash storage device. For more information, see the Capacity section in this document. The hibernation file is the same size as the RAM. 10

12 We recommend disabling the hibernation file for ULCPCs that have 2 GB flash storage devices because of the limited capacity of the storage device. If the flash storage device has greater capacity and the hibernation file is necessary for the user scenario, you may want to enable the hibernation file. Summary of Design Considerations The following list summarizes the hardware recommendations included in this document: CPU speed should be at least 500 MHz and optimally 900MHz. Choosing a CPU with a higher speed can further improve performance. For the flash storage device: The speed of the flash storage device should support read and write speeds of 5 MB per second or higher. Because compression increases CPU usage and the number of writes to the flash storage device, we recommend you investigate how typical use will impact Windows XP performance under a specified user scenario. The capacity should be determined by your user scenario based on the calculations for the total size of Windows XP including Windows XP runtime features and add-ins, applications, and user data. When calculating the lifetime of the flash storage device, take into consideration erase cycles, capacity, and controller efficiency, and make sure the lifetime of the storage device is equal to the ULCPC lifetime. The flash storage device should be contained inside of the ULCPC case. We recommend an ATA interface because it is natively supported in Windows XP and will reduce design and development time, which will help get ULCPCs to customers faster. The RAM should be at least 256 MB and optimally 1 GHz, which is greater than the system requirement specified for Windows XP. Choosing to install more RAM can improve performance. The minimum Windows XP system requirements may not be sufficient to run Windows and additional applications on an ULCPC if page file is disabled. The following list summarizes the Windows XP performance recommendations included in this document: The page file should be disabled for 2 GB flash storage devices. For all other flash storage device capacities, consider the user scenario. If you choose to enable the page file, determine the working set of the largest application scenario to determine a minimum size for your page file. The crash dump file should be disabled for 2 GB flash storage devices if the page file is disabled. For all other flash storage device capacities, consider the user scenario. If you choose to enable the crash dump file, the page file must be enabled as well. The hibernation file should be disabled for 2 GB flash storage devices. For all other flash storage device capacities, consider the user scenario. 11

13 Additional Resources Windows Driver Kit. This kit describes the Windows operating system storage architecture and contains information about different types of storage devices. For additional information, see: Windows Logo Kit. This kit provides information on certification, driver signing, and logos. Windows Logo Kit can help you get your ULCPC certified. For more information, see: 12