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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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RL01 and RL02 drives are moving head magnetic disk drives manufactured by Digital Equipment Corporation for the PDP-8 and PDP-11 microcomputers. The RL01 and RL02 drives stored approximate 5MB and 10MB respectively, utilizing a removable data cartridge.[1]: 1–3 The drives are typically mounted in a standard 19" rack and weigh 34 kg. Up to four RL02 or RL01 drives may be used, in any combination, from a single controller. Typically an RL11 in the case of a Unibus PDP-11 and an RLV11 or RLV12 in the case of a Q-bus PDP-11. On the PDP-8/a the controller is an RL8A which consists of an M8433 Hex wide Omnibus card.
The RL01 and RL02 data cartridges are based on IBM 5440 cartridges, but have servo tracking data pre-encoded onto the cartridge.[1]: 1–3 This reduces the need for strict head alignment, allowing cartridges to be used in several drives (although there was no backwards compatibility between RL02 and RL01 cartridges, despite similar appearance[1]: 1–4 ). However, this prevents on-site low level formatting of cartridges. The drives have logic to prevent this servo data from being overwritten.[1]: 1–3 RL01 cartridges have 256 tracks, and RL02 cartridges have 512 tracks.[1]: 1–3
On both RL01 and RL02 cartridges, each track is divided into 40 sectors of equal length. Each sector is divided into six fields, defined as follows (where each word is 16 bits).[1]: 1–4 )
The header and data is preceded by two servo bursts (S1 and S2) which are prerecorded onto the data cartridge during manufacture. Data is encoded on the disk using Modified Frequency Modulation, where a one bit will result in a magnetic flux reversal on the magnetic coating of the cartridge.
The last track of an RL01 and RL02 cartridge contains a table which lists all of the bad sectors on the cartridge. This track also contains the cartridges serial number.[1]: 1-6–1-8 ) The drive does not contain any logic for handling bad sectors - this must be performed by the operating system. Hence, one could potentially erase this table if the operating system does not prevent against it.
Access to and from an RL drive is done serially, via a 40 pin cable running from the controller inside the computer to the drive. These lines are described in the table below.[2]
| Line Name | Description | Direction |
|---|---|---|
| Drive Select 0 | These two lines are used to select the drive (0–3). As there are only four possible combinations, at least one of the four drives is always selected. Only the selected drive will output data on the Drive Ready through to Status lines. | From the controller to the RL drive. |
| Drive Select 1 | ||
| Write Gate | Only when this line is asserted will the writing circuitry be enabled within the drive. If this line is asserted while a sector pulse occurs, the drive will raise a Write Gate Error and the drive will no longer accept any commands. | |
| Write Data | When the Write Gate line is asserted, data may be transferred on this line. This data should be encoded in Modified Frequency Modulation, as the drive does not encode or decode this data. | |
| System Clock | The system clock shifts data through the Drive Command line and also provides a reference for the disk servo motor. The drive will not spin up without these clock pulses. The clock pulses must be 4.1 MHz +/- 0.1%. | |
| Drive Command | This line is used to transfer the drive command word, shifted by the system clock. | |
| Power Fail | This line remains asserted at all times that the controller is active. If the computer or controller experience a power failure, this line will fall low, resulting in the drive unloading the heads and spinning down the platter. | |
| Drive Ready | This line will be asserted by the selected drive when the head is centred over the selected track, indicating that the drive is ready to receive commands from the controller. This temporarily goes low when a drive command word has been shifted. | From the RL drive to the controller. |
| Status Clock | This clock the delayed system clock and is only enabled during a transfer of the drive status word. | |
| Sector Pulse | This is a 625 microsecond pulse which is asserted high 40 times per disc revolution. This signal is generated from by the sector transducer. | |
| Read Data | Modified Frequency Modulation encoded data is transferred over this line whenever the drive is selected and the head is locked onto a track. | |
| Drive Error | This line is asserted when there has been certain drive errors. | |
| Status | The drive status word is transferred in serial using this line, clocked by the Status Clock. |
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
RL01 and RL02 drives are moving head magnetic disk drives manufactured by Digital Equipment Corporation for the PDP-8 and PDP-11 microcomputers. The RL01 and RL02 drives stored approximate 5MB and 10MB respectively, utilizing a removable data cartridge. The drives are typically mounted in a standard 19" rack and weigh 34 kg. Up to four RL02 or RL01 drives may be used, in any combination, from a single controller. Typically an RL11 in the case of a Unibus PDP-11 and an RLV11 or RLV12 in the case of a Q-bus PDP-11. On the PDP-8/a the controller is an RL8A which consists of an M8433 Hex wide Omnibus card.
The PDP-11 is a series of 16-bit minicomputers originally sold by Digital Equipment Corporation (DEC) from 1970 into the late 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were sold, making it one of DEC's most successful product lines. The PDP-11 is considered by some experts to be the most popular minicomputer. The PDP-11 included a number of innovative features in its instruction set and additional general-purpose registers that made it easier to program than earlier models in the PDP series. Further, the innovative Unibus system allowed external devices to be more easily interfaced to the system using direct memory access, opening the system to a wide variety of peripherals. The PDP-11 replaced the PDP-8 in many real-time computing applications, although both product lines lived in parallel for more than 10 years. The ease of programming of the PDP-11 made it popular for general-purpose computing. The design of the PDP-11 inspired the design of late-1970s microprocessors including the Intel x86 and the Motorola 68000. The design features of PDP-11 operating systems, and other operating systems from Digital Equipment, influenced the design of operating systems such as CP/M and hence also MS-DOS. The first officially named version of Unix ran on the PDP-11/20 in 1970. It is commonly stated that the C programming language took advantage of several low-level PDP-11–dependent programming features, albeit not originally by design. An effort to expand the PDP-11 from 16- to 32-bit addressing led to the VAX-11 design, which took part of its name from the PDP-11.
The North–South Commuter Railway (NSCR), also known as the Clark–Calamba Railway, is a 147-kilometer (91-mile) commuter rail system under construction on the island of Luzon in the Philippines. Running from New Clark City in Capas, Tarlac, to Calamba, Laguna, with 36 stations and four services, the railway is designed to improve connectivity within the Greater Manila Area and will be integrated with the railway network in the region. Originally planned in the 1990s, the railway project has had a tumultuous history, being repeatedly halted and restarted for various reasons. The first proposals were the 32-kilometer (20-mile) "Manila–Clark rapid railway" with Spain in the 1990s, alongside the "Manila–Calabarzon Express". During the 2000s, the Northrail project with China was initiated but discontinued in 2011 due to allegations of overpricing. The railway's current incarnation began development in 2013. The project's initial phase was approved in 2015, and construction began in 2019. Expected to cost ₱873.62 billion, the line is the most expensive railway transportation project in the country. The entire system is expected to be completed by the third quarter of 2033.
RT-11 (Real-time 11) is a discontinued small, low-end, single-user real-time operating system for the full line of Digital Equipment Corporation PDP-11 16-bit computers. RT-11 was first implemented in 1970 and released in June 1973. It was widely used for real-time computing systems, process control, and data acquisition across all PDP-11s. It was also used for low-cost general-use computing.
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 →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
