Difference between revisions of "Standard Disk Interconnect"
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| − | '''Standard Disk Interconnect''' ('''SDI''') is a [[DEC]] designed disk drive to controller interface offering high performance, availability, and configuration flexibility. | + | The '''Standard Disk Interconnect''' ('''SDI''') is a [[Digital Equipment Corporation|DEC]] designed [[disk]] [[drive]] to [[device controller|controller]] interface offering high performance, availability, and configuration flexibility. |
| − | These characteristics make it suitable for use with [[PDP-11]]s and with [[VAX]] single and multiple [[CPU]] systems. | + | These characteristics make it suitable for use with [[PDP-11]]s and with [[VAX]] single and multiple [[Central Processing Unit|CPU]] systems. |
== SDI Family of DSA Products == | == SDI Family of DSA Products == | ||
| − | The family of [[DSA]] products which implement the SDI consists of: | + | The family of [[Digital Storage Architecture|DSA]] products which implement the SDI consists of: |
| + | |||
* SDI Disk controllers: | * SDI Disk controllers: | ||
** [[KDA50]] ([[QBUS]]) | ** [[KDA50]] ([[QBUS]]) | ||
| − | ** [[KDB50]] ([[VAXBI]]) | + | ** [[KDB50]] ([[VAX Bus Interconnect|VAXBI]]) |
| − | ** [[KDM70]] ([[XMI]]) | + | ** [[KDM70]] ([[Extended Memory Interconnect|XMI]]) |
** [[UDA50]] ([[UNIBUS]]) | ** [[UDA50]] ([[UNIBUS]]) | ||
* SDI Disk Drives: | * SDI Disk Drives: | ||
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== SDI Features == | == SDI Features == | ||
| − | To support | + | To support DSA data integrity goals and provide compatibility and interchange, SDI controllers include advanced data integrity features: |
| − | * An advanced [[ | + | * An advanced [[Error-correction code|Error Correction Code]] (ECC) more than seven times as powerful as the industry's most common code. |
* An [[EDC|Error Detection Code]] (EDC) which verifies ECC computation logic and the ECC correction process, checks controller data paths, and indicates a forced error in case a hard media error causes sector replacement. | * An [[EDC|Error Detection Code]] (EDC) which verifies ECC computation logic and the ECC correction process, checks controller data paths, and indicates a forced error in case a hard media error causes sector replacement. | ||
* A Bad Block Replacement Algorithm which dynamically substitutes good blocks for potentially defective ones. The goal of the DSA is to anticipate developing defects and retire blocks containing them before user data loss occurs. | * A Bad Block Replacement Algorithm which dynamically substitutes good blocks for potentially defective ones. The goal of the DSA is to anticipate developing defects and retire blocks containing them before user data loss occurs. | ||
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== SDI Interconnect == | == SDI Interconnect == | ||
| − | The SDI drive to controller interconnect is a serial bus which connects each drive directly, or radially, to its controller. | + | The SDI drive to controller interconnect is a [[serial]] [[bus]] which connects each drive directly, or radially, to its controller. |
| − | Electrically, SDI consists of four coaxial signal carriers, two for moving user data, commands, and responses between drive and controller, and two for continuous real time transmission of drive and controller status information. | + | Electrically, SDI consists of four [[coaxial cable|coaxial]] signal carriers, two for moving user data, commands, and responses between drive and controller, and two for continuous real time transmission of drive and controller status information. |
| − | The SDI is transformer coupled, so drive and controller do not require a common DC ground. | + | The SDI is [[transformer]] coupled, so drive and controller do not require a common [[direct current|DC]] [[ground]]. |
| − | Transformer coupling both eliminates unpredictable and unrepeatable "ground loop" problems, and provides for installation flexibility, since SDI drives can be physically added to or removed from a subsystem without disrupting its operation. | + | Transformer coupling both eliminates unpredictable and unrepeatable "[[ground loop]]" problems, and provides for installation flexibility, since SDI drives can be physically added to or removed from a subsystem without disrupting its operation. |
| − | Logically, SDI consists of a protocol by which a controller can recognize a drive's characteristics, direct its mechanical operation, store data on or retrieve data from it, and recognize and | + | Logically, SDI consists of a [[protocol]] by which a controller can recognize a drive's characteristics, direct its mechanical operation, store data on or retrieve data from it, and recognize and recover from error conditions. |
| − | recover from error conditions. | ||
Revision as of 13:05, 21 August 2022
The Standard Disk Interconnect (SDI) is a DEC designed disk drive to controller interface offering high performance, availability, and configuration flexibility. These characteristics make it suitable for use with PDP-11s and with VAX single and multiple CPU systems.
SDI Family of DSA Products
The family of DSA products which implement the SDI consists of:
- SDI Disk controllers:
- SDI Disk Drives:
- SDI Solid State Disk Drives
SDI Features
To support DSA data integrity goals and provide compatibility and interchange, SDI controllers include advanced data integrity features:
- An advanced Error Correction Code (ECC) more than seven times as powerful as the industry's most common code.
- An Error Detection Code (EDC) which verifies ECC computation logic and the ECC correction process, checks controller data paths, and indicates a forced error in case a hard media error causes sector replacement.
- A Bad Block Replacement Algorithm which dynamically substitutes good blocks for potentially defective ones. The goal of the DSA is to anticipate developing defects and retire blocks containing them before user data loss occurs.
- Automatic Revectoring for transparent access to replaced blocks.
- Quadruplicate Headers for verification of read/write head position prior to data transfer, even if media defects exist in the header area.
- Firewalling against single failure points to detect and isolate single component failures so that no erroneous data is passed to the user.
SDI Interconnect
The SDI drive to controller interconnect is a serial bus which connects each drive directly, or radially, to its controller.
Electrically, SDI consists of four coaxial signal carriers, two for moving user data, commands, and responses between drive and controller, and two for continuous real time transmission of drive and controller status information. The SDI is transformer coupled, so drive and controller do not require a common DC ground. Transformer coupling both eliminates unpredictable and unrepeatable "ground loop" problems, and provides for installation flexibility, since SDI drives can be physically added to or removed from a subsystem without disrupting its operation.
Logically, SDI consists of a protocol by which a controller can recognize a drive's characteristics, direct its mechanical operation, store data on or retrieve data from it, and recognize and recover from error conditions.
