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In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
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
 | This article relies on a single source. (September 2014) |
Multi-level queueing, used at least since the late 1950s/early 1960s, is a queue with a predefined number of levels. Items get assigned to a particular level at insert (using some predefined algorithm), and thus cannot be moved to another level (unlike in the multilevel feedback queue). Items get removed from the queue by removing all items from a level, and then moving to the next. If an item is added to a level above, the "fetching" restarts from there. Each level of the queue is free to use its own scheduling, thus adding greater flexibility than merely having multiple levels in a queue.
Multi-level queue [1]: 196 scheduling algorithm is used in scenarios where the processes can be classified into groups based on property like process type, CPU time, IO access, memory size, etc. One general classification of the processes is foreground processes and background processes. In a multi-level queue scheduling algorithm, there will be 'n' number of queues, where 'n' is the number of groups the processes are classified into. Each queue will be assigned a priority and will have its own scheduling algorithm like Round-robin scheduling[1]: 194 or FCFS. For the process in a queue to execute, all the queues of priority higher than it should be empty, meaning the process in those high priority queues should have completed its execution. In this scheduling algorithm, once assigned to a queue, the process will not move to any other queues.
Consider the following table with the arrival time, execute time and type of the process (foreground or background - where foreground processes are given high priority) to understand non pre-emptive and pre-emptive multilevel scheduling in depth with FCFS algorithm for both the queues:
| Process Name | Arrival Time | Execute Time | Type |
|---|---|---|---|
| P0 | 0 | 5 | Foreground |
| P1 | 1 | 8 | Background |
| P2 | 3 | 7 | Background |
| P3 | 4 | 3 | Foreground |
| P4 | 5 | 3 | Foreground |
| P5 | 8 | 11 | Background |
| P6 | 15 | 3 | Foreground |
| P7 | 25 | 4 | Foreground |
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Multi-level queueing, used at least since the late 1950s/early 1960s, is a queue with a predefined number of levels. Items get assigned to a particular level at insert (using some predefined algorithm), and thus cannot be moved to another level (unlike in the multilevel feedback queue). Items get removed from the queue by removing all items from a level, and then moving to the next. If an item is added to a level above, the "fetching" restarts from there. Each level of the queue is free to use its own scheduling, thus adding greater flexibility than merely having multiple levels in a queue.
In computer science, a multilevel feedback queue is a scheduling algorithm. Scheduling algorithms are designed to have some process running at all times to keep the central processing unit (CPU) busy. The multilevel feedback queue extends standard algorithms with the following design requirements: Separate processes into multiple ready queues based on their need for the processor. Give preference to processes with short CPU bursts. Give preference to processes with high I/O bursts. (I/O bound processes will sleep in the wait queue to give other processes CPU time.) The multilevel feedback queue was first developed by Fernando J. Corbató (1962). For this accomplishment, the Association for Computing Machinery awarded Corbató the Turing Award.
In computer science, an input queue is a collection of processes in storage that are waiting to be brought into memory to run a program. Input queues are mainly used in Operating System Scheduling which is a technique for distributing resources among processes. Input queues not only apply to operating systems (OS), but may also be applied to scheduling inside networking devices. The purpose of scheduling is to ensure resources are being distributed fairly and effectively; therefore, it improves the performance of the system. Essentially, a queue is a collection which has data added in the rear position and removed from the front position. There are many different types of queues, and the ways they operate may be totally different. Operating systems use First-Come, First-Served queues, Shortest remaining time, Fixed-priority pre-emptive scheduling, round-robin scheduling and multilevel queue scheduling. Network devices use First-In-First-Out queue, Weighted fair queue, Priority queue and Custom queue.
In computer science, a monotone priority queue is a variant of the priority queue abstract data type in which the priorities of extracted items are required to form a monotonic sequence. That is, for a priority queue in which each successively extracted item is the one with the minimum priority (a min-heap), the minimum priority should be monotonically increasing. Conversely for a max-heap the maximum priority should be monotonically decreasing. The assumption of monotonicity arises naturally in several applications of priority queues, and can be used as a simplifying assumption to speed up certain types of priority queues. A necessary and sufficient condition on a monotone priority queue is that one never attempts to add an element with lower priority than the most recently extracted one.
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 →The Greenwood District.