Virtual STORAGE Access Method(VSAM) is a disk storage system.

It was implemented in OS/VS2 operating system.

SUBSEQUENTLY, it was used through out the MVS architecture.

VSAM comprises of the following access methods:

ESDS: Entry Sequence Data Set

KSDS: Key Sequence Data Set

RRDS: Relative Data Set

VSAM records can be of FIXED or variable length.

These are organized in fixed size blocks, known as Control Intervals, and later into larger divisions known as Control Areas.

CI sizes are measured in terms of bytes, while CA sizes are measured in terms of disk tracks or cylinders.

ESDS : It contains the files which are interface specific and

accessed through Relative Byte Address

KSDS : It contains the files which are interface specific and accessed through a secondary index

RRDS : It contains the files which are interface specific and accessed through Relative Record Number

Each file has two objects.

1. File object - represents the file itself. The methods of the file are used to perform
DELETE,READ,REWRITE,UNLOCK,WRITE,STARTBR operations.
2. FileBrowse object - represents a browse operations on the file and the methods are used to perform
ENDBR,READNEXT,READPREV,RESETBR

Virtual Storage Access Method(VSAM) is a disk storage system.

It was implemented in OS/VS2 operating system.

Subsequently, it was used through out the MVS architecture.

VSAM comprises of the following access methods:

ESDS: Entry Sequence Data Set

KSDS: Key Sequence Data Set

RRDS: Relative Data Set

VSAM records can be of fixed or variable length.

These are organized in fixed size blocks, known as Control Intervals, and later into larger divisions known as Control Areas.

CI sizes are measured in terms of bytes, while CA sizes are measured in terms of disk tracks or cylinders.

ESDS : It contains the files which are interface specific and

accessed through Relative Byte Address

KSDS : It contains the files which are interface specific and accessed through a secondary index

RRDS : It contains the files which are interface specific and accessed through Relative Record Number

Each file has two objects.