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A RAM drive (also called a RAM disk) is a block of random-access memory (primary storage or volatile memory) that a computer's software is treating as if the memory were a disk drive (secondary storage). It is sometimes referred to as a "virtual RAM drive" or "software RAM drive" to distinguish it from a "hardware RAM drive" that uses separate hardware containing RAM, which is a type of battery backed solid-state drive. == Performance == The performance of a RAM drive is in general orders of magnitude faster than other forms of storage media, such as an SSD, hard drive, tape drive, or optical drive. This performance gain is due to multiple factors, including access time, maximum throughput and type of file system, as well as others. File access time is greatly reduced since a RAM drive is solid state (no mechanical parts). A physical hard drive or optical media, such as CD-ROM, DVD, and Blu-ray must move a head or optical eye into position and tape drives must wind or rewind to a particular position on the media before reading or writing can occur. RAM drives can access data with only the memory address of a given file, with no movement, alignment or positioning necessary. Second, the maximum throughput of a RAM drive is limited by the speed of the RAM, the data bus, and the CPU of the computer. Other forms of storage media are further limited by the speed of the storage bus, such as IDE (PATA), SATA, USB or Firewire. Compounding this limitation is the speed of the actual mechanics of the drive motors, heads and/or eyes. Third, the file system in use, such as NTFS, HFS, UFS, ext2, etc., uses extra accesses, reads and writes to the drive, which although small, can add up quickly, especially in the event of many small files vs. few larger files (temporary internet folders, web caches, etc.). Because the storage is in RAM, it is volatile memory, which means it will be lost in the event of power loss, whether intentional (computer reboot or shutdown) or accidental (power failure or system crash). This is, in general, a weakness (the data must periodically be backed up to a persistent-storage medium to avoid loss), but is sometimes desirable: for example, when working with a decrypted copy of an encrypted file. In many cases, the data stored on the RAM drive is created from data permanently stored elsewhere, for faster access, and is re-created on the RAM drive when the system reboots. Apart from the risk of data loss, the major limitation of RAM drives is their limited capacity, which is constrained by the amount of RAM within the machine. Multi-terabyte-capacity persistent storage has become commoditized as of 2012, whereas RAM is still measured in gigabytes. RAM drives use the normal RAM in main memory as if it were a partition on a hard drive rather than actually accessing the data bus normally used for secondary storage. Though RAM drives can often be supported directly from the operating system via special mechanisms in the operating system kernel, it is possible to also create and manage a RAM drive by an application. Usually no battery backup is needed due to the temporary nature of the information stored in the RAM drive, but an uninterrupted power supply can keep the entire system running during a power outage, if necessary. Some RAM drives use a compressed file system such as cramfs to allow compressed data to be accessed on the fly, without decompressing it first. This is convenient because RAM drives are often small due to the higher price per byte than conventional hard drive storage. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ram drive」の詳細全文を読む スポンサード リンク
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