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In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
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
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A disk controller is a controller circuit that enables a CPU to communicate with a hard disk, floppy disk or other kind of disk drive. It also provides an interface between the disk drive and the bus connecting it to the rest of the system.[1][2]
Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card. Modified frequency modulation (MFM) controllers were the most common type in small computers, used for both floppy disk and hard disk drives. Run length limited (RLL) controllers used an improved line code to increase storage efficiency by about 50%. Priam created a proprietary storage algorithm that could double the disk storage. Shugart Associates Systems Interface (SASI) was a predecessor to SCSI.
Modern disk controllers are integrated into the disk drive as peripheral controllers. For example, SCSI disks have built-in SCSI controllers. In the past, before most SCSI controller functionality was implemented in a single chip, separate SCSI controllers interfaced disks to the SCSI bus.
These integrated peripheral controllers communicate with a host adapter in the host system over a standardized, high-level storage bus interface. The most common type of interface provided nowadays by host controllers is Serial ATA for home use. High-end disks also use Serial Attached SCSI or Fibre Channel. The peripheral controller integrated on PATA (IDE), Serial ATA, Parallel SCSI or Serial Attached SCSI hard disks is usually a microcontroller or an ASIC.
Disk controllers can also control the timing of access to flash memory, which is not mechanical in nature (i.e., no spinning disk).
The component that allows a computer to talk to a peripheral bus is a host adapter or host bus adapter (HBA, e.g., Advanced Host Controller Interface). A disk controller allows a disk to talk to the same bus. Signals read by a disk read-and-write head are converted by a disk controller, then transmitted over the peripheral bus, then converted again by the host adapter into the suitable format for the motherboard's bus, and then read by the CPU into the memory (RAM).
Sometimes there may be yet another controller between a host adapter and a disk controller - a disk array controller that allows hardware RAID to be formed. Sometimes it may be even physically integrated with an HBA.
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A disk controller is a controller circuit that enables a CPU to communicate with a hard disk, floppy disk or other kind of disk drive. It also provides an interface between the disk drive and the bus connecting it to the rest of the system. Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card. Modified frequency modulation (MFM) controllers were the most common type in small computers, used for both floppy disk and hard disk drives. Run length limited (RLL) controllers used an improved line code to increase storage efficiency by about 50%. Priam created a proprietary storage algorithm that could double the disk storage. Shugart Associates Systems Interface (SASI) was a predecessor to SCSI. Modern disk controllers are integrated into the disk drive as peripheral controllers. For example, SCSI disks have built-in SCSI controllers. In the past, before most SCSI controller functionality was implemented in a single chip, separate SCSI controllers interfaced disks to the SCSI bus. These integrated peripheral controllers communicate with a host adapter in the host system over a standardized, high-level storage bus interface. The most common type of interface provided nowadays by host controllers is Serial ATA for home use. High-end disks also use Serial Attached SCSI or Fibre Channel. The peripheral controller integrated on PATA (IDE), Serial ATA, Parallel SCSI or Serial Attached SCSI hard disks is usually a microcontroller or an ASIC. Disk controllers can also control the timing of access to flash memory, which is not mechanical in nature (i.e., no spinning disk).
A floppy disk controller (FDC) is a hardware component that directs and controls reading from and writing to a computer's floppy disk drive (FDD). It has evolved from a discrete set of components on one or more circuit boards to a special-purpose integrated circuit (IC or "chip") or a component thereof. An FDC is responsible for reading data presented from the host computer and converting it to the drive's on-disk format using one of a number of encoding schemes, like FM encoding (single density) or MFM encoding (double density), and reading those formats and returning it to its original binary values. Depending on the platform, data transfers between the controller and host computer would be controlled by the computer's own microprocessor, or an inexpensive dedicated microprocessor like the MOS 6507 or Zilog Z80. Early controllers required additional circuitry to perform specific tasks like providing clock signals and setting various options. Later designs included more of this functionality on the controller and reduced the complexity of the external circuitry; single-chip solutions were common by the later 1980s. By the 1990s, the floppy disk was increasingly giving way to hard drives, which required similar controllers. In these systems, the controller also often combined a microcontroller to handle data transfer over standardized connectors like SCSI and IDE that could be used with any computer. In more modern systems, the FDC, if present at all, is typically part of the many functions provided by a single super I/O chip.
A forensic disk controller or hardware write-block device is a specialized type of computer hard disk controller made for the purpose of gaining read-only access to computer hard drives without the risk of damaging the drive's contents. The device is named forensic because its most common application is for use in investigations where a computer hard drive may contain evidence. Such a controller historically has been made in the form of a dongle that fits between a computer and an IDE or SCSI hard drive, but with the advent of USB and SATA, forensic disk controllers supporting these newer technologies have become widespread. Steve Bress and Mark Menz invented hard drive write blocking (US Patent 6,813,682). A device which is installed between a storage media under investigation and an investigator's computer is called a "bridge kit". The bridge kit has one connector for the storage media and another connector the investigator's computer. It allows the investigator to read, but not alter the device under investigation. The United States National Institute of Justice operates a Computer Forensics Tool Testing (CFTT) program which formally identifies the following top-level tool requirements: A hardware write block (HWB) device shall not transmit a command to a protected storage device that modifies the data on the storage device. An HWB device shall return the data requested by a read operation. An HWB device shall return without modification any access-significant information requested from the drive. Any error condition reported by the storage device to the HWB device shall be reported to the host.
A disk array controller is a device that manages the physical disk drives and presents them to the computer as logical units. It often implements hardware RAID, thus it is sometimes referred to as RAID controller. It also often provides additional disk cache. Disk array controller is often ambiguously shortened to disk controller which can also refer to the circuitry responsible for managing internal disk drive operations.
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 →Madam C.J. Walker