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ReadyBoost (codenamed EMD) is a disk caching software component developed by
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...
for
Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...
and included in later versions of
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
. ReadyBoost enables NAND memory
mass storage In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. In general, the term is used as large in relation to contemporaneous hard disk drives, but it has been used large in relati ...
CompactFlash CompactFlash (CF) is a flash memory mass storage device used mainly in portable electronic devices. The format was specified and the devices were first manufactured by SanDisk in 1994. CompactFlash became one of the most successful of the e ...
, SD card, and
USB flash drive Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply ( interfacing) between computers, peripherals and other computers. A bro ...
devices to be used as a cache between the
hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with mag ...
and
random access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...
in an effort to increase computing performance. ReadyBoost relies on the SuperFetch and also adjusts its cache based on user activity. ReadyDrive for hybrid drives is implemented in a manner similar to ReadyBoost.


Overview

Using ReadyBoost-capable flash memory ( NAND memory devices) for caching allows
Windows Vista Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, which was released five years before, at the time being the longest time span between successive releases of ...
and later to service random disk reads with better performance than without the cache. This caching applies to all disk content, not just the page file or system DLLs. USB flash devices typically are slower than a mechanical hard disk for sequential I/O, so, to maximize performance, ReadyBoost includes logic that recognizes large, sequential read requests and has the hard disk service these requests. When a compatible device is plugged in, the Windows AutoPlay dialog offers an additional option to use the flash drive to speed up the system; an additional ReadyBoost tab is added to the drive's properties dialog where the amount of space to be used can be configured. The minimum cache size is 250 MB. In Vista or with FAT32 formatting of the drive, the maximum is 4 GB. In Windows 7 or later with NTFS or exFAT formatting, the maximum cache size is 32 GB per device. Windows Vista allows only one device to be used, while Windows 7 allows multiple caches, one per device, up to a total of 256 GB. ReadyBoost compresses and encrypts all data that is placed on the flash device with
AES-128 The Advanced Encryption Standard (AES), also known by its original name Rijndael (), is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is a variant ...
; Microsoft has stated that a 2:1 compression ratio is typical, so a 4 GB cache would usually contain 8 GB of data.


Requirements

For a device to be compatible and useful, it must conform to these requirements: * The removable media's capacity must be at least 256 MB (250 MB after formatting,
Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...
reports in its Event Log a required minimum of 235 MB). *
Windows 7 Windows 7 is a major release of the Windows NT operating system developed by Microsoft. It was Software release life cycle#Release to manufacturing (RTM), released to manufacturing on July 22, 2009, and became generally available on October 22, ...
allows up to eight devices for a maximum of 256 GB of additional memory, with up to 32 GB on a single storage device. * The device must have an access time of 1 ms or less. * The device must be capable of 2.5 MB/s read speeds for 4 kB random reads spread uniformly across the entire device, and 1.75 MB/s write speeds for 512 kB random writes spread uniformly across the device. * The Microsoft Windows Client Performance group recommends a flash-memory-to-system-RAM ratio of between 1:1 and 2.5:1. Other considerations: * Vista's ReadyBoost supports NTFS, FAT16, and FAT32 from SP1 onwards. Windows 7 also supports the newer exFAT file system. As the ReadyBoost cache is stored as a file, the flash drive must be formatted as FAT32, NTFS, or exFAT in order to have a cache size greater than FAT16's 2 GB filesize limit; if the desired cache size is 4 GB (the FAT32 filesize limit) or larger, the drive must be formatted as NTFS or exFAT. The performance differences between these file systems are negligible with ReadyBoost. * The initial release of ReadyBoost for Windows Vista supported one device. Windows 7 supports multiple flash drives for ReadyBoost, so performance improvement similar to RAID 0 can be expected. * The ReadyBoost algorithm was improved in Windows 7, resulting in better performance. One experiment showed reading of flash memory up to 5–10 times faster than Windows Vista due to higher hit rate. * Because ReadyBoost stores its cache as a file on the root directory of the drive rather than using the flash memory without a file system, the file system must be mounted and assigned a drive letter. The ReadyBoost cache is created on the
root directory In a computer file system, and primarily used in the Unix and Unix-like operating systems, the root directory is the first or top-most directory in a hierarchy. It can be likened to the trunk of a tree, as the starting point where all branche ...
of the drive. * If the system drive (the primary drive, with Windows system files on it) is a solid-state drive (SSD), ReadyBoost is disabled, since reading from that drive would be at least as fast as reading from the ReadyBoost drive. * ReadyBoost caches all data as it is being written to the local hard disk: "the Ecache.sys device driver intercepts all reads and writes to local hard disk volumes (C:\, for example), and copies any data being written into the caching file that the service created." SuperFetch pre-populates frequently-read data into ReadyBoost cache, so SuperFetch is necessary for ReadyBoost to perform well. * ReadyBoost is not compatible with portable media devices such as
mobile phones A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link while ...
or
cameras A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with a ...
, or other devices with emulated storage. ReadyBoost is not available on
Windows Server 2008 Windows Server 2008 is the fourth release of the Windows Server operating system produced by Microsoft as part of the Windows NT family of the operating systems. It was released to manufacturing on February 4, 2008, and generally to retail on F ...
.


Performance

A system with 512 MB of RAM (the minimum requirement for Windows Vista) can see significant gains from ReadyBoost. In one test case, adding 1 GB of ReadyBoost memory sped up an operation from 11.7 seconds to 2 seconds. However, increasing the physical memory (RAM) from 512 MB to 1 GB (without ReadyBoost) reduced it to 0.8 seconds. System performance with ReadyBoost can be monitored by Windows Performance Monitor. As the price of RAM decreased and more RAM was installed in computers, the mitigations provided by ReadyBoost to systems with insufficient memory decreased. The core idea of ReadyBoost is that a
flash memory Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both use ...
(e.g. a
USB flash drive Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply ( interfacing) between computers, peripherals and other computers. A bro ...
or an
SSD A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is a ...
) has a much faster seek time than a typical magnetic hard disk (less than 1 ms), allowing it to satisfy requests faster than reading files from the hard disk. It also leverages the inherent advantage of two parallel sources from which to read data, whereas Windows 7 enables the use of up to eight flash drives at once, allowing up to nine parallel sources. USB 2.0 flash drives are slower for ''sequential'' reads and writes than modern desktop hard drives. Desktop hard drives can sustain anywhere from 2 to 10 times the transfer speed of USB 2.0 flash drives but are equal to or slower than USB 3.0 and Firewire (IEEE 1394) for sequential data. USB 2.0 and faster flash drives have faster ''random access'' times: typically around 1 ms, compared to 12 ms for mainstream desktop hard drives. On
laptop A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a clam shell form factor with the screen mounted on the inside of the upper li ...
computers, the performance shifts more in favor of flash memory when laptop memory is more expensive than desktop memory; many laptops also have relatively slow 4200 rpm and 5400 rpm hard drives. In the original release of Windows Vista, ReadyBoost failed to recognize its cache data upon resume from sleep, and restarted the caching process, making ReadyBoost ineffective on machines undergoing frequent sleep/wake cycles. This problem was fixed with Vista SP1.


Limitations

Since flash drives wear out after a finite (though very large) number of writes, ReadyBoost will eventually wear out the drive it uses. According to the Microsoft Windows Client Performance group, the drive should be able to operate for at least ten years.


See also

* Automated Tiering * Features new to Windows Vista *
Hybrid array A hybrid array is a form of hierarchical storage management that combines hard disk drives (HDDs) with solid-state drives (SSDs) for I/O speed improvements. Hybrid storage arrays aim to mitigate the ever increasing price-performance gap between H ...
* Hybrid drive *
Windows Vista I/O technologies Windows Vista introduced a number of new I/O functions to the Microsoft Windows line of operating systems. They are intended to shorten the time taken to boot the system, improve the responsiveness of the system, and improve the reliability of ...
*
Windows To Go Windows To Go is a feature in Windows 8 Enterprise, Windows 8.1 Enterprise, Windows 10 Education and Windows 10 Enterprise versions prior to the May 2020 update, that allows the system to boot and run from certain USB mass storage devices such ...


References

{{Reflist, 30em


External links


Windows 7 features: ReadyBoost

Windows Vista: Features Explained: Windows ReadyBoost

Windows Vista Help Page on ReadyBoost

Windows Vista: Features Explained: Performance Features (of which ReadyBoost is one)

Channel9 interview with Michael Fortin on ReadyBoost and other performance technologies in Windows Vista

Section STORAGE-009 in Windows Logo Program Requirements Suite, Version 3.09

Understand ReadyBoost and whether it will Speed Up your System

Microsoft's Software Patent on ReadyBoost

AnandTech: Windows Vista Performance Guide - ReadyBoost, ReadyBoost Performance Analysis, and Hard Drive Performance and ReadyBoost

In depth Tom's Hardware article with analyses of ReadyBoost and Superfetch
Windows Vista Windows 7 Windows 8 Repurposing Solid-state caching Windows components Windows NT architecture