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What is a file?
A named collection.
Where are files stored?
On magnetic and optical disks. Files are grouped into directories (folders in GU).
What is a filename extension?
A short set of characters on the end of a file's name that is used to distinguish the types of data being stored in different files.
What are the two major ways files are organized and accessed?
- 1) sequential - The records in the file are organized as a list and are retrieved and processed one at a time from the beginning to the end of the file.
- 2) direct access - The records in the file are arranged so an individual record may be retrieved without examining other records in the file.
What are some advantages and disadvantages of sequential file access?
- Easy to program
- Allows simple file structures
- Well suited to many common programming applications
- -Poor access performance
To implement direct access in file organization, an indexed directory is often _______________.
stored in memory
What is stored in the directory that is stored in memory to facilitate direct access?
Often a table containing a *key* and the location of that record within the file.
What do hashed files do?
- Hashed files provide direct access to the records in a file without the overhead or an indexed directory. Hashing doesn't use a unique key, but stores values in buckets related to some data that they contain.
- For example, adding together the digits of a phone number then using the ones digit of the result could be a hash.
What is the purpose of directories (or folders)?
To organize files within a computer system. Directores and folders are usually hierarchical.
Accessing secondary memory is one of the ________ time consuming aspects of processing, so a primary goal is to ensure that such access is handled as ____________ as possible.
One way to effeciently access secondary memory is to _____________________________________________.
have the read write head read data while they are searching for data as well as when they are moving away from the requested data.