MS-DOS implements random access to files using a combination of file control blocks (FCBs) and the file system's structure. When a file is opened, the system retrieves its FCB, which contains information such as the file's size and current position. Random access is achieved by allowing the user to move the file pointer to any position within the file using commands like SEEK
, enabling read and write operations from that specific location without needing to read through the entire file sequentially. This direct access is facilitated by the underlying disk structure and the way MS-DOS manages file I/O operations.
Sequential access,Random, Binary
The common techniques of file processing include sequential access, random access, and direct access. Sequential access involves reading data sequentially from the beginning to the end of a file. Random access allows reading data from any part of the file without having to read the preceding data. Direct access uses a key or address to locate specific data within the file.
Random access simply means the ability to read and write anywhere in the file, as opposed to sequential access where data is simply appended to the end of the file and is accessed by traversing from the start of the file in sequential order. Random access is ideally suited to data arrays where every element in the file is exactly the same length, allowing constant-time traversal from one element to any other, in both directions. If the data is also sorted, random access also allows binary search to improve search efficiency.
A swap file is the file that an operating system uses when it is moving data. A computer creates this file when it is moving data from random access memory to virtual memory.
Sequential and random access.
The language itself doesn't say anything about the purpose of a file, that's up to the programmer to decide.
random access memory means when you open a file its saved here to keep it running :-)
A serial access file has data stored on it in the order in which it was written. Each new record goes at the end of the file. To read a record from the file it is necessary to read through all the preceding records first.A sequential access file has data stored on it in the order of the data in a key field.A direct access file is one where any record can be accessed without having to access other records first. This is also known as random access.
To access a particular data item in a sequential file, you need to read in all items in the file prior to the item of interest. This works acceptably well for small data files of unstructured data, but for large, structured files, this process is time-consuming and wasteful. Sometimes, we need to access data in non-sequential ways. Files which allow non-sequential access are random access files.
non-volatile random access memory
In BASIC the put command fills a file field area, typically for random access writes.
There is no difference in the files, only in the way they are accessed. Sequential files are accessed just like they sound, sequentially, which means the if you want to read something that starts at byte number 40,000, you have to read and ignore the first 39,999 bytes. Random-access files, however, allow you to go directly to the exact location you want. Sequential access is normally used if the file is stored on a medium which doesn't allow random access. For example, if the file is stored on tape, you have to start reading from the beginning of the tape, until you get to the location you want. If you're using a hard disk, however, the head that reads and writes the disc can be moved directly to the portion of the file you want, making it faster to get the data you want.