Page 112 - Accounting Information Systems

CHAPT E R 2 Introduction to Transaction Processing 83

FI G U R E
2-36 AHARD DISK PACK

000 399
Track 100
400 Cylinders

Access Mechanism 11 Disks

10 Access Arms
20 Tracks
20 Read/Write Heads (Cylinder 100)

Optical Disks

Optical disks are growing in popularity. The advantage of optical disks is that they can store very large
amounts of data. A compact disc, one type of optical disk, is as portable as a floppy disk but can store
more than 600 MB of data. There are several types of optical disk storage systems, including CD-ROM,
WORM, and erasable optical disks.
A CD-ROM (compact disc read-only memory) is a secondary storage device that contains data or
programs imprinted by the manufacturer. However, the user cannot write to (alter) the data on the CD
because it is a read-only device. The WORM (write-once, read-many) disk is a secondary storage device
that allows the user to write to the disk one time. An erasable optical disk allows the user to store and
modify data on the disk many times.

Section B: Legacy Systems

defining feature of legacy systems is their use of flat files for data storage. The following section
presents a review of data structures and the flat-file processing techniques that evolved from
A them. It then examines data processing methods that employ these flat-file structures. The sec-
tion concludes with a detailed explanation of the program logic underlying flat-file update procedures.

Data Structures

Data structures constitute the physical and logical arrangement of data in files and databases. Under-
standing how data are organized and accessed is central to understanding transaction processing. Data