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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
The Digital Storage Systems Interconnect (DSSI) is a computer bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems. It was designed as a smaller and lower-cost replacement for the earlier DEC Computer Interconnect that would be more suitable for use in office environments. DSSI was superseded by Parallel SCSI.[1]
It was introduced in 1988 and has a bandwidth of 32 Mbit/s (4 MB/sec) and was typically limited to a length of 25 metres (82 ft). DSSI support was later extended to MIPS-based DECsystems and DEC Alpha-based AlphaServer systems.
DSSI peripherals could be distinguished from narrow SCSI devices by their characteristic five-conductor power connector featuring an extra lead intended for Battery/UPS connection to power critical components in the event of a power failure.
The major characteristics of the DSSI bus are:
Bus Length Allowable Offset
Meters/Feet (DC) (AC)
----------- ----------------
up to 20/65 200mv 70mv (rms)
20-25/65-82 40mv 14mv (rms)
VAX6000 QUAD-Host--> 27/89 30mv 10.5mv (rms)
VAX7000
VAX10000
DSSI SUPPORT IN OpenVMS: OpenVMS VAX V5.0-2: o Single- and Dual-Host support with 2 EDA640s (MicroVAX 3300/3400 series). o Systems Communications Services (SCS) for the VMScluster is run over the Network Interconnect (NI) for MicroVAX 3300/3400. OpenVMS VAX V5.1: o Standalone support for the KFQSA. o Up to 6 ISEs on a single DSSI bus regardless of whether 1 or 2 hosts systems are attached to the bus. OpenVMS VAX V5.1-1: o Dual host support for KFQSAs (1 KFQSA per system). OpenVMS VAX V5.2: o For 3300/3400 series, SCS communication over the DSSI. o Multiple KFQSA's per system, but *not* multiple dual-hosted DSSI's per system (here, multiple means 2, since only 2 hosts are allowed on the DSSI bus). o DSSI adapter must connect to another like adapter, e.g. EDA640 to EDA640 or KFQSA to KFQSA. o Up to 7 ISEs on a single DSSI bus when only 1 host system is attached to the bus. OpenVMS VAX V5.3: o Mixed DSSI adapters, i.e. EDA640 to KFQSA. o Mixed DSSI adapters, i.e. EDA640 to KFQSA. o Double dual-host configurations, i.e. 2 DSSI buses between two CPUs. Each bus is terminated at its own pair of adapters. OpenVMS VAX V5.3-2: o Support for VAX 4000. (The VAX 4000 has 2 SHACs and can support two KFQSAs on the bus, so it can have up to 4 DSSI buses). OpenVMS VAX V5.4-2: o Support for the KFMSA, an XMI to DSSI adapter. The KFMSA may only be used to single-host a VAX 6000 model or dual-host 2 VAX 6000 models together. OpenVMS VAX V5.4-3: o Tri-host configurations supported. OpenVMS VAX V5.5-2: o Quad-host configurations with VAX 6000, VAX 7000/10000 series systems now supported. NOTE: KFQSAs do not support SCS communication over the DSSI bus, they MUST have a NI connection in order to run the cluster software. OpenVMS Alpha V1.5, OpenVMS VAX V6.0: o Quad-host DSSI configurations with DEC 4000 AXP systems supported. DEC 4000 systems can be configured only as end nodes on a DSSI bus, therefore, quad-host configurations must include at least two VAX systems. o KFQSA Q-bus to DSSI configurations supported. VAX processors that use the KFQSA adapter can be placed on the same DSSI bus as DEC 4000 processors.
Other companies, such as CMD and Symbios Logic made DSSI compatible chipsets or peripherals, for example, CMD manufactured various models of the CDI-4000 which would allow SCSI peripherals to be used on a DSSI bus.
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The Digital Storage Systems Interconnect (DSSI) is a computer bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems. It was designed as a smaller and lower-cost replacement for the earlier DEC Computer Interconnect that would be more suitable for use in office environments. DSSI was superseded by Parallel SCSI. It was introduced in 1988 and has a bandwidth of 32 Mbit/s (4 MB/sec) and was typically limited to a length of 25 metres (82 ft). DSSI support was later extended to MIPS-based DECsystems and DEC Alpha-based AlphaServer systems. DSSI peripherals could be distinguished from narrow SCSI devices by their characteristic five-conductor power connector featuring an extra lead intended for Battery/UPS connection to power critical components in the event of a power failure.
DSSI may refer to: Digital Storage Systems Interconnect Disposable Soft Synth Interface German School Seoul International (Deutsche Schule Seoul International)
The Standard Disk Interconnect (SDI, sometimes Standard Disk Interface) was used by Digital Equipment Corporation for its line of RAxx disks, for example the RA90. There were two bi-directional serial communications paths between the controller and the drive. One path was for messages (from the controller to the drive) and responses (from the drive to the controller); messages controlled seeking, setting drive parameters, reporting errors, etc. This path was also used to transmit data to and from the drive. The other path consisted of a continuously transmitted set of control (controller-to-drive) or status (drive-to-controller) bits. There were about 6 bits in each direction, and they served the same purpose as having six dedicated lines in each direction. By encoding control signals serially they could be AC-coupled (with a transformer) to prevent ground loop problems and EMI issues between the controller and the drives, which could be connected by long cables, even to different floors in a building. The same serial interconnect was used for tape and solid state storage devices to the storage subsystem controllers. Large VAX systems primarily used the Hierarchical Storage Controller (HSC) series but Unibus and BI Bus controllers to SDI were built as well. The UDA50 for the Unibus was the first controller shipped with the SDI interface. Among the signals the drive sent to the controller were: Index Pulse - the drive head is over the beginning of sector 0 of the track. Sector Pulse - the drive head is over the beginning of some other sector. The controller counted these pulses to know where the drive was, rotationally. Read/Write Ready - the drive head has settled over some track, and it is safe to read or write. The controller signals to the drive included signals such as Read Gate (turn the Read Head on) and Write Gate (turn the Write Head on). The data transfer could be over a wide range of bit rates as the system was self clocked. This enabled multiple generations of disk technology to use the SDI, as well as other storage devices. The SDI was an element of the Digital Storage Architecture (DSA) which included the Mass Storage Control Protocol (MSCP), which specified communications means between OS software and all flavors of storage devices.
Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises a series of digital images displayed in rapid succession, usually at 24, 25, 30, or 60 frames per second. Digital video has many advantages, such as easy copying, multicasting, sharing and storage. Digital video was first introduced commercially in 1986 with the Sony D1 format, which recorded an uncompressed standard-definition component video signal in digital form. In addition to uncompressed formats, popular compressed digital video formats today include MPEG-2, H.264 and AV1. Modern interconnect standards used for playback of digital video include HDMI, DisplayPort, Digital Visual Interface (DVI) and serial digital interface (SDI). Digital video can be copied and reproduced with no degradation in quality. In contrast, when analog sources are copied, they experience generation loss. Digital video can be stored on digital media such as Blu-ray, on computer data storage, or streamed over the Internet to end users who watch content on a personal computer or mobile device screen or a digital smart TV. Today, digital video content such as TV shows and movies also includes a digital audio soundtrack.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.
