Monolithic structure of operating system pdf

It is named after one of its developers, Dick Pick. Being hash-file oriented, Pick provides efficiency in data access time. Today a Pick system can also natively access host files in Windows or Unix monolithic structure of operating system pdf any format.

A Pick database is divided into one or more accounts, master dictionaries, dictionaries, files and sub-files, each of which is a hash-table oriented file. These files contain records made up of fields, sub-fields and sub-sub-fields. All elements are variable-length, with field and values marked off by special delimiters, so that any file, record, or field may contain any number of entries of the lower level of entity. The master dictionary is similar to a directory in that it stores pointers to other dictionaries, files and executable programs. The master dictionary also contains the command-line language. This uniformity is exploited throughout the system, both by system functions, and by the system administration commands.

For example, the ‘find’ command will find and report the occurrence of a word or phrase in a file, and can operate on any account, dictionary, file or sub-file. Each record must have a unique, primary key which determines where in a file that record is stored. Within a bucket, records are scanned sequentially. This same method is used to write the record back to its correct “bucket”. Files can contain an unlimited number of records, but retrieval efficiency is determined by the number of records relative to the number of buckets allocated to the file. All modern multi-value databases have a special file-type which changes extent dynamically as the file is used.

All files start as a contiguous group of disk pages, and grow by linking additional “overflow” pages from unused disk space. Initial Pick implementations had no index structures as they were not deemed necessary. Pick data files are usually two levels. The first level is known as the “dictionary” level and is mandatory. Files created with only one level are, by default, dictionary files. Some versions of the Pick system allow multiple data levels to be linked to one dictionary level file, in which case there would be multiple data-level identifiers in the dictionary file.

Pick allows for multiple, pre-computed field aliases. File cross-connects or joins are handled as a synonym definition of the foreign key. A customer’s data, such as name and address, are “joined” from the customer file into the invoice file via a synonym definition of “customer number” in the “invoice” dictionary. Managing large, sparse data sets in this way can result in efficient use of storage space.

This is why these databases are sometimes called NF2 or NF-squared databases. Cheyenne Helicopter project required developing a database. ENGLISH did not fully allow manipulating the 3-dimensional multivalued structure of data records. He licensed “Pick” to a large variety of manufacturers and vendors who have produced different “flavors” of Pick. Dick Pick died of stroke complications in October 1994. What most characterizes Pick is the design and features of the database and the associated retrieval language. The Pick database was licensed to roughly three dozen licensees between 1978 and 1984, some of which are included in this list.

Application-compatible implementations evolved into derivatives and also inspired similar systems. On the assembler level, all references were to addresses on the disk, rather than RAM. Software: Intermediate software translated the already existing programming into the native machine language, usually on microprocessors. The system and database were implemented in an application that simulated most of the Pick functions, like the Basic and retrieval languages. In general, they depended on their host operating systems for everything else, from disk mapping to security. The first commercial release was in 1973. 80s and were based in Hemel Hempstead, England.