A System Deployment Image (aka SDI) is a file format used primarily with Microsoft

Microsoft

Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

 products to contain an arbitrary disk image

Disk image

A disk image is a single file or storage device containing the complete contents and structure representing a data storage medium or device, such as a hard drive, tape drive, floppy disk, CD/DVD/BD, or USB flash drive, although an image of an optical disc may be referred to as an optical disc image...

, including boot sector information.

Description

The SDI file format is often used to allow the use of a virtual disk via mounting Some versions of Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 allow for "RAM booting

Booting

In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...

", which is essentially the ability to load an SDI file into memory and then boot from it. The SDI file format also lends itself to network booting using the Preboot Execution Environment

Preboot Execution Environment

The Preboot eXecution Environment is an environment to boot computers using a network interface independently of data storage devices or installed operating systems.PXE was introduced as part of the Wired for Management framework by Intel and is described in the specification The Preboot...

 (PXE). Another usage is hard disk imaging

Disk image

A disk image is a single file or storage device containing the complete contents and structure representing a data storage medium or device, such as a hard drive, tape drive, floppy disk, CD/DVD/BD, or USB flash drive, although an image of an optical disc may be referred to as an optical disc image...

.
The SDI file itself is partitioned into the following sections:

Boot BLOB

Blob

- In biology :* Blob , sections of the visual cortex where groups of color-sensitive neurons assemble* Globster, an unidentified organic mass that washes up on the shoreline of an ocean or other body of water...

 : This contains the actual boot program, STARTROM.COM. This is analogous to the boot sector of a hard disk.
Load BLOB : This typically contains NTLDR

NTLDR

NTLDR is the boot loader for all releases of Windows NT operating system up to and including Windows XP and Windows Server 2003. NTLDR is typically run from the primary hard disk drive, but it can also run from portable storage devices such as a CD-ROM, USB flash drive, or floppy disk...

 and is launched by the boot BLOB.
Part BLOB : This contains the actual boot runtime (i.e. the contents of the disk image including any OS files) and also includes the boot.ini (used by NTLDR) and ntdetect.com files which should be located within the root directory of the runtime. The size of the runtime cannot exceed 500 Mb. In addition to this requirement the runtime must also be capable of dealing with the fact that it is booting from a ramdisk. This implies that the runtime must include the "Windows RAM Disk

RAM disk

A RAM disk or RAM drive is a block of RAM that a computer's software is treating as if the memory were a disk drive...

 Driver" component (specified within the boot.ini).

Disk BLOB : This is flat HDD image starting with a MBR

Master boot record

A master boot record is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk...

. It is used for hard drive imaging instead of booting. Also only Disk BLOBs can be mounted with Microsoft's utilities.

SDI usually contains either Disk BLOB (HD cloning or temporary SDI) or three other of them (bootable SDI).

Windows Vista

Windows Vista

Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...

 or Windows PE

Windows Preinstallation Environment

Windows Preinstallation Environment is a lightweight version of Windows XP, Windows Server 2003, Windows Vista, Windows 7, or Windows Server 2008 R2 that is used for the deployment of workstations and servers...

 2.0 boot sequence includes boot.sdi file, which contains Part BLOB for empty NTFS

NTFS

NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....

 volume and Table-of-Contents slot for WIM image, which is stored actually not inside the SDI, but in separate on-disk file.

SDI driver

SDI files can be mounted as virtual disk drives and assigned a drive letter if an SDI driver is available to allow this. A SDI driver is a type of storage driver and is commonly used with Windows XP Embedded.

SDI management

Microsoft provides a tool called the "SDI File Manager" (sdimgr.exe) which can be used for the purpose of manipulating SDI files. Some of the tasks which this tool facilitates are:

• The creation of an SDI image file.
• The creation of an SDI image file from an existing hard disk partition.
• The verification of an existing SDI image.

SDI loader

The mechanism which allows for the creation, addition and removal of virtual disk drives. SDI Loader and Driver work with Disk BLOB.