2. RECORD :
It is the collection of related data values and items.It
describes the entities and attributes.
eg : Employee record .
RECORD TYPES :
It is the collection of field names and their
corresponding data types.
A data type specifies the types of values of a field.
3. FILE:
It is a sequence of records.
There are two types of files depending upon the size
1. Fixed length record
2. Variable length record
Fixed length record :
Every record in a file are same size.
Variable length record :
Different records in a file are different size.
:
4. • File become variable length record depends
1.The file records are same record type but one or more
fields are different size.
2. File records are same record type but one or more field
have multiple values for individual record.
3. Files are same record type but some fields are optional.
4. Files contain records of different record types and
varying length.
5. RECORD BLOCKS
• Records of file are stored in disk blocks.Each block
contain numerous records.
bfr = floor (B/R) records per block.
unused space = B-(bfr*R)bytes
where bfr is the blocking factor.
B is the size of block b.
R is the size of fixed length records.
6. SPANNED Vs UNSPANNED
Spanned :
It stores one part of a record in one block and the rest
in the other .
Unspanned :
The records are not allow to cross block boundries.
Each block may contain different number of records.
number of blocks for r records
b = ceil (r/bfr)blocks
7. ALLOCATING FILE BLOCKS ON DISK
There are three types allocation
1. Contiguous allocation
2. Linked allocation
3. Indexed allocation
Contiguous allocation
The file blocks are allocated to consecutive disk
blocks.
Linked allocation
Each file block contain a pointer to the next block.
Indexed allocation
One or more index blocks contain pointes to the
actual blocks.
8. FILE HEADER
• It contain information about a file that is needed by the
system programs that access the file records.
• It also include the information to determine the disk
address,record format of a file.
