Aug 1999 SW204 : Software and Files Design (Question 4) Suggested Solutions

(a)	One of the most common reasons for poor system performance is slow disk access. Poor performance can be improved by caching, and reducing the amount of disk arm movement.
	(i) Define caching, and describe how it can improve system performance. (ii) Define disk arm movement, and describe how it can improve system performance.	[3] [3]]
	(i) Caching is a collection of blocks kept in primary memory. An algorithm checks if the required blocks of information are found in the primary memory; if not, the required information is copied in the cache. (ii) Disk arm movement refers to the read/write head which reads information from storage. One way of reducing disk arm movement is to store data in sequence; alternatively a fixed read/write head might be used.
(b)	File system reliability can be improved by using backups. Explain each of the following terms: (i) Dumping (ii) Incremental dumping	[2] [2]
	(i) Dumping involves the entire information found on a disk being copied over to another disk. (ii) Incremental dumping involves making a dump periodically, with daily dumps being made of those files which have been changed.
(c)	Give two reasons why two copies of the File Allocation Table are maintained.	[2]
	To provide integrity and reliability.
(d)	Alba Trading Company Pte Ltd operates in a standard manner in a consumer sale industry. There has been a large expansion of its businesses volume over the past few years. This has meant that the management has found it increasingly difficult to obtain timely and reliable statistics on consumer sales by product line and sales by customer category. The company has a small Data Processing department, which consists of a Systems Analyst and a Programmer cum Computer Operator. The management has decided to purchase and install and 'Order Billing With Sales Analysis' software package, which has to be operational within months. (i) List four major factors which should be considered when any software package is being selected. (ii) Describe the problems which might have arisen if each of these factors were to be overlooked.	[4] [4]
	(i) Hardware compatibility. User requirements. Cost effectiveness. An ability to interface with the current system. Vendor support. (ii) Any suitable solutions accepted.