RAM DISK

May 2009Roman Okolovich

Introduction (1 of 2)

A RAM Disk is a software layer that enables applications to transparently use RAM, often a segment of main memory, as if it were a hard disk or other secondary storage. Access time may be greatly improved to files held on

RAM disks compared to data held on other secondary storage.

The volatility of RAM means that data will be lost if power is lost, e.g. when the computer is turned off.

From privacy point of view, RAM disk is also a working drive for decrypted version of encrypted documents.

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Introduction (2 of 2) A RAM disk can perfectly be used to store web content of web servers. temporary index files and tables of database servers ( MS-SQL-Server,

MySQL, etc). temporary files ( TEMP and TMP environment variable) and

“Temporary Internet Files” the scratch disk for Adobe (R) Photoshop (R). games and installed programs. The startup times of programs may

decrease drastically! audio and video capture / editing. creation and playback of slide shows. the printer spool folder. data that has to be written to CD, to prevent underrun during the

burn process. as storage of the “ReadyBoost” cache on Vista. all kinds of data that may be lost (or MUST be lost for security

reasons) at shutdown.

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Computer Architecture Overview Central processing unit (CPU, or simply a processor)

It actually operates on data, performs any calculations, and controls all the other components

Processor cache is an intermediate stage between ultra-fast registers and much slower main memory. It's introduced solely to increase performance of the computer (primary cache and secondary cache).

Random access memory (usually known by its acronym, RAM) It is directly or indirectly connected to the CPU via a memory bus.

It is actually comprised of two buses (not on the diagram): an address bus and a data bus.

fast but temporary storage

Hard Disk (Secondary storage) is not directly accessible by the CPU. The computer usually uses

its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds.

The time taken to access a given byte of information stored in RAM is measured in billionths of a second, or nanoseconds.

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RAM Disk utilities

There are plenty of utilities available in Windows Microsoft Ramdisk

“RAMDisk” for Windows 2000 / XP / Server 2003 / Vista / Server 2008 / Windows 7

Ramdisk

ImDisk Virtual Disk Driver

Other operation systems tmpfs - a modern way of using RAM under Unix-like

operating systems

mdconfig - RAM disk in FreeBSD

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RAM disk utilities: Microsoft Ramdisk (1 of 4) Microsoft Ramdisk is a sample that demonstrates a

software-only Windows(r) 2000 device driver. This driver creates a RAM disk drive of a specified size. You can use this Ramdisk like any other disk, but the contents of the disk are lost when you shut down the computer.

Disadvantages Source code only DDK is needed (not free) This sample provides an example of a minimal driver.

Neither the driver nor the sample programs are intended for use in a production environment. Rather, they are intended for educational purposes and as a skeletal version of a driver.

64 Mb size disk limit

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RAM disk utilities: “RAMDisk” (2 of 4) The RAMDisk “Enterprise” covers following features:

One unique 32-bit and 64-bit versions that runs on all 32-bit (64-bit) versions of Windows 2000 , XP , Server 2003/2008 and Vista (monoprocessor or multiprocessor )

Auto formatting to FAT12 , FAT16 , FAT32 or NTFS / NTFS with compression

Auto resizing to the maximal available (or allowed) ramdisk size

Comprehensive fine tuning of the available memory to balance maximal ramdisk size against OS stability

Easy to use and to configure from within the device tree of Device Manager

Increased ramdisk sizes, theoretically to up to 64 GB using PAE (Physical Address Extension) and if supported by the OS. (The /PAE switch may be needed in boot.ini on systems that use more than 4 GB physical RAM).

Ability to load a raw disk image to format and populate the ramdisk at driver initialization (load speed : ~ 30 sec/GB using an image stored on a mode 4 IDE ATA HD with a 1.2 Ghz processor).

Ability to save the content to a raw disk image at shutdown and at regular intervals or at particular times.

Advantages The ramdisk is available for the 32-bit and 64-bit OS's

This RAMDisk has the capability to automatically reload an image file at boot time ( and before other services / programs are started ) and to save the ramdisk content at shutdown and/or at regular intervals.

Disadvantages Not free

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RAM disk utilities: Ramdisk (3 of 4)

Freeware RRamdisk.sys, originally written by Gavotte based on Microsoft’s Ramdisk.sys. It stable, doesn’t have size limitation, supports popular

FAT16, FAT32, NTFS file systems, and supports Windows 2000 operating system and above including Vista.

Advantages Installation is not needed

Free

Disadvantages It doesn’t support command line

Not good documentation

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RAM disk utilities: ImDisk Virtual Disk Driver (4 of 4)

ImDisk is a virtual disk driver for Windows NT/2000/XP/2003/Vista/2008 It can use one or more disk image files to create virtual

hard disk, floppy or CD/DVD drives. The install package installs a console-mode control

program called imdisk.exe and a Control Panel applet.

Advantage Free Possible to run the ImDisk driver automatically at boot

time

Disadvantage On Vista (32-bit and 64-bit versions) and Server 2008 you

need to either turn off UAC, User Access Control, or setup the driver to auto-load on system startup.

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Using ImDisk

imdisk -a -s 1Gb -m r: (imdisk -a -s 200Mb -m r:)

format r: /fs:FAT32 /V:RamDisk /Q /y

imdisk -d -m r:

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Windows Sysinternals: Junction Windows 2000 and higher supports directory symbolic links, where a

directory serves as a symbolic link to another directory on the computer. For example, if the directory D:\SYMLINK specified C:\WINNT\SYSTEM32 as

its target, then an application accessing D:\SYMLINK\DRIVERS would in reality be accessing C:\WINNT\SYSTEM32\DRIVERS.

Directory symbolic links are known as NTFS junctions in Windows. Windows comes with no tools for creating junctions—you have to

purchase the Win2K Resource Kit, which comes with the linkd program for creating junctions.

Mark Russinovich has written his own junction-creating tool: Junction. Junction not only allows you to create NTFS junctions, it allows you to see if

files or directories are actually reparse points. Reparse points are the mechanism on which NTFS junctions are based, and they are used by Windows' Remote Storage Service (RSS), as well as volume mount points.

Example: > junction.exe x:\temp c:\temp

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References

RAM disk utilities Microsoft Ramdisk

Ramdisk

“RAMDisk” for Windows 2000 / XP / Server 2003 / Vista / Server 2008 / Windows 7

ImDisk Virtual Disk Driver

Junction v1.05

Memory Support and Windows Operating Systems

Wikipedia Computer data storage

RAM disk

Physical Address Extension

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