Access sequential

The memory subsystem on most supercomputers is organized to support maximum performance on loops of stride one, or when the elements of an array are accessed sequentially with no gaps. In general, the stride is defined by... 

PYI —Collection of records that normally consist of matching types of fields. Records in a file may be accessed sequentially (the entire file must be read until the needed record is reached) or randomly (the record contains a key field, which determines its physical location in storage). 

In processes where solid material is fed into containers such as bags or drums at the end of the production line, it may not be logistically feasible or it may take too much time to wait until all containers are filled to select a random sample. The containers would have to be stored somewhere until all of them were filled. Then those selected for the sample would have to be retrieved. Or if the process were continuous and we shipped the product as soon as a truck could be loaded, then we would never have an entire lot from which to sample. The following method can be used for obtaining a random sample of discrete units when the lot items are accessible sequentially (Kennedy and Gentle, 1980). 

Another typical problem occurs when computer displays must be requested and accessed sequentially by the user, which makes greater memory demands upon the operator, negatively affecting difficult decision-making tasks [14]. With conventional instrumentation, all process information is constantly available to the operator an overall view of the process state can be obtained by a glance at the console. Detailed readings may be needed only if some deviation from normal conditions is detected. 

Speed of access is very quick because, if a file is being accessed sequentially, the records within it are read first sector following sector and then track following track before moving to another cylinder, with the movement of the read/write heads minimized. 

These earlier machines did not have random access memory, which had not been invented yet. Data were stored on a rotating drum, so they could only be accessed sequentially. The first memory became available to us for the IBM 650 in about 1959. The memory device was the size of a desk and had a capacity of 12 bytes, but it sped up the calculations by perhaps a factor of 2 or 3. (Yes, that is bytes, not kilobytes or megabytes.)... 

Fig. 5 (right part) presents the four functions accessible sequentially via key "num lock". Menus are cyclic, for example to reach PFL function user press three times (modulo four) key "num lock". 

Technology can be a powerful external driver. Much has been written about how the internet transformed the supply chain. It transformed from being linear as shown in Fig. 1.2, where information could only be accessed sequentially between functions, to a nonlinear system shown in Fig. 1.3, where any function could access information from any other. 

The functionality available in MedChem Explorer is broken down into a list of available computational experiments, including activity prediction, align/ pharmacophore, overlay molecules, conformer generation, property calculation, and database access. Within each experiment, the Web system walks the user through a series of questions that must be answered sequentially. The task is then submitted to a remote server, where it is performed. The user can view the progress of the work in their Web browser at any time. Once complete, the results of the calculation are stored on the server. The user can then run subsequent experiments starting with those results. The Web interface includes links to help pages at every step of the process. 

A brief review has appeared covering the use of metal-free initiators in living anionic polymerizations of acrylates and a comparison with Du Font s group-transfer polymerization method (149). Tetrabutylammonium thiolates mn room temperature polymerizations to quantitative conversions yielding polymers of narrow molecular weight distributions in dipolar aprotic solvents. Block copolymers are accessible through sequential monomer additions (149—151) and interfacial polymerizations (152,153). 

Depending on the ring substituent, trifluoromethoxyben2enes can be made by the sequential chlorination—fluorination of anisole(s) (351—354). A one-step process with commercial potential is the BF (or SbF2)-cataly2ed reaction of phenol with carbon tetrachloride/hydrogen fluoride (355). Aryl trifluoromethyl ethers, which may not be accessible by the above routes,may be made by fluorination of aryl fluoroformates or aryl chlorothioformates with sulfur tetrafluoride (348) or molybdenum hexafluoride (356). 

File—External (physical) only may be sequential or random access. 

File handling statements allow the manipulation of sequential and random access files. (Since there is considerable variation from one system to the next, the following information is given in general terms only.) Devices are treated... 

File manager systems—Maintain files and handle data input to and output from the files. Database management systems (DBMS) contain integrated sets of files related by their use and provide uniform software interfaces for accessing data. The essential relationships between records in the files may be of several types, including sequential, associative, or hierarchical. 

All setup data and results are stored in Data Resource Files rather than standard sequential or random access files. This has turned out to be a key feature contributing to a flexible and low maintenance system. These are ASCII files which can be typed to the screen, printed, or edited with a word processor. They contain information organized by variable name, value, and units. The following is an example of a data resource file ... 

Data Resource Files allow the user to access all pertinent data as needed, reducing the need for programmer support or hard code to access specialized variables. The data storage format is very user friendly in that if a user wishes to make changes, he can comment fields as desired and does not need to worry about a formatted sequential file sti ucture. 

Jacobi reports using a variant of method A to access the A,B,E-ring system of wortmannin.14 The sequential addition of methyl lithium and acetylenic Grignard reagent followed by triflation proceeds from 7 to the corresponding triflate 8 in 74% yield (Fig. 4.13). Subsequent carbonylation of the alkyne and the phenol produces the acyl oxazole 9, which is smoothly converted into the furanolactone 10 over three more steps. 

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