• not able to directly manipulate the hardware
• may need to wait for translation before running
• the program may be less efficient.

Direct Change-Over

• A date is chosen for the shutdown of the old system, then at that time, the old system
  is turned off and the new system is implemented

Phased

• Parts of the new system are implemented in stages or for a period of time, both the old and the new system are running together until all parts of the system are implemented.

• It transfers data signals from one node directly to another in the network without broadcasting

• Data Integrity: they provide ways or mechanisms for enforcing data integrity constraints, such as referential integrity. If a record in the parent table is deleted, related records in the child table also get deleted. This ensures accurthe acy and consistency of data stored in the database
• Data Security
• Concurrency control
• Reduces data redundancy
• Data retrieval and querying
• Data indexing
• Data consistency and acid transaction
• Data backup and recovery
• Data sharing and collaboration
• Convenient data maintenance

Phased:
Advantages:

• only a small part of the operation affected if new system fails
•  no need to pay for two sets of wages

Disadvantages:

•  time consuming (each part needs testing fully before expanding system)

Pilot:
Advantages:

• if new system fails, only that part will be affected
• possible to gradually train staff on pilot before whole system changes over

Disadvantages:

•  time consuming (waiting to see how pilot works before rolling out to rest of the organisation)

Direct:
Advantages:

•  less likely to malfunction since fully tested
• immediate benefits/less time wasted
•  reduced costs (only one system so no need to duplicate staff)

Disadvantages:

• disastrous if the new systems does fail

Parallel:
Advantages:

•  if new system goes down, there is a backup system in place
• possible to gradually train staff/staff have time to get used to the new system

• Physical topology deals with the placement of nodes
• Logical topology deals with the data flow  in the network

• two's complement has only one value for zero

Direct changeover – new system replaces existing system immediately/overnight

 Parallel running – new system runs alongside/together with existing system

Parallel running – there is always the old system to fall back on in the event of the new system failing/information is not lost/always a second copy

Direct changeover – if things go wrong lose all data/old system is not available

Direct changeover – training is more difficult to organise

Parallel running – training can be gradual Parallel running is more expensive to implement than direct changeover....

Direct changeover is a quicker method of implementation than parallel running

Direct Changeover: The old system is stopped completely, and the new system is started. All of the data that used to be input into the old system, now goes into the new one.

 Parallel Running: The new system is started, but the old system is kept running in parallel (side-by-side) for a while. All of the data that is input into the old system, is also input into the new one. Eventually, the old system will be stopped, but only when the new system has been proven to work.

It has a header

• that contains the destination address
• that contains the packet number
• that contains the originator’s address

It has a payload

It has a trailer.

1. Primary Storage (Memory):

   • Random Access Memory (RAM): This is a volatile memory used to store data and instructions that the CPU (Central Processing Unit) can access quickly. RAM is essential for running applications and the operating system. However, its contents are lost when the computer is powered off.
   • Read-Only Memory (ROM): ROM is a non-volatile memory that stores essential firmware and instructions necessary for the computer's boot-up process. It retains its contents even when the power is turned off.
   • Cache Memory: Cache is a small and fast memory located closer to the CPU. It stores frequently accessed data to speed up the processing.

2. Secondary Storage (Mass Storage):

   • Hard Disk Drive (HDD): HDDs use magnetic storage to store data on rotating platters. They provide relatively large storage capacities and are commonly used in computers and laptops for long-term data storage.
   • Solid-State Drive (SSD): SSDs use NAND flash memory to store data, offering faster read and write speeds than HDDs. They are more durable and consume less power, making them increasingly popular in modern computers.
   • Optical Discs: CDs, DVDs, and Blu-ray discs are examples of optical storage media. They are mainly used for distribution of software, music, movies, and archival purposes.
   • USB Flash Drives: Also known as thumb drives or pen drives, these portable storage devices use flash memory to store data and can be easily connected to a computer's USB port.
   • Memory Cards: Memory cards, such as SD cards and microSD cards, are used in various devices like cameras, smartphones, and tablets to store data, photos, videos, etc.
   • External Hard Drives: These are HDDs or SSDs contained within an external enclosure, allowing users to expand their computer's storage capacity or create backups.

Advantages

• on-line catalogues can be viewed
• much larger choice of products
• product reviews obtainable before purchase
• orders placed over internet any time day or night
• download software purchased straight away
• good and services usually cheaper on the internet
• programs that can search for best price/cheapest
• very fast placing an order has been placed as customer name, address
• and credit card details are stored so no need to re enter
• buy goods from anywhere in the world
• no need to go to shop/save travelling time

Disadvantages

• spam
• need a credit card to shop on-line/not everyone has a credit card
• hackers could retrieve credit card numbers and use them to buy goods
• security fears - of giving credit card number over the internet/fraud
• goods must be delivered/can not have the goods immediately
• can not touch/handle/see the goods

Syntax
• An error that occurs when a command does not follow the expected syntax of the language, e.g. when a keyword is incorrectly spelt
• Incorrect: IF A ADN B Then
• Correct: IF A AND B Then

Logical
• An error that causes a program to output an incorrect answer (that does not necessarily crash the program)
• An algorithm that calculates a person’s age from their date of birth, but ends up giving negative numbers

Multi-tasking - It is a data processing modes where a single CPU processing more than one task or program apparently at the same time

Time-sharing - a processing mode where a single CPU processes tasks from more than one user apparently at the same time

Time-sharing - this is a processing mode in which the CPU serves two or more users with different processing requirements ( tasks)

On-line processing - is a mode of processing where the result of data processing transaction is available immediately

Real-time processing - is a mode of data processing in which the time interval required to process and respond to inputs is so small that the response itself is useful for controlling the physical activity of a process

1. Application
2. Presentation
3. Session
4. Transport
5. Network
6. Data link
7. Physical

• OS controls operation of system/hardware
• Applications software allows the system to do something useful

1. Identify any computer output device suitable for each of the following tasks:

1. Generating receipts where carbon copies are required  (1mk)

• Impact printers e.g dot matrix

     b) an architectural drawing where precision is required         (1mk)

• Plotter

(c ) producing document output for a visually impaired person (1mk)

• Braille/speakers

1. Pesa Tele has offices in Nairobi and Kampala connected in a network . the management is convinced that someone is illegally gaining access to the data in their computers. State three ways in which the company can overcome this problem (3mks)

• Encryption
• Firewall
• Audit trail/tracking
• Use of passwords
• Limit the number of log-in attempts

1. Explain two ways in which the use of internet could make reporting of corruption easier (4mks)

• Interactive: the internet based technology enables real-time dialogue hence instantaneous reporting of cases
• Outreach: the technology allows the coverage of wide areas
• Social mobilization : it easy to create a network of people with similar concerns
• Anonymity : it is easier to report corruption without being  known
• Security: the message sent reaches destination without being intruded

1. State ways in which software errors can be prevent during program development

• Use of antivirus software
• Performing system update frequently
• Testing the software before implementation
• Proper training

• Firmware is a software program permanently etched into a hardware device such as a keyboards, hard drive, BIOS, or video cards.
• Device drivers are operating system-specific and hardware-dependent. A device driver acts as a translator between the hardware device and the programs or operating systems that use it. 
• Firmware is a software that controls a system, and firmware's functionality ranges from performing basic tasks like minimal I/O controls to full-fledged software system running with simple or no OS, with scheduler, memory management, etc. 
• A driver, on the other hand, is usually part of the operating system that performs the specific task of controlling a hardware component like a display or USB controller, etc., and gives an interface to use the hardware by Operating system and applications.

• It is the use of proofing tools like spelling and grammar checkers and autocorrects to check whether a document has typographical or grammatical errors

• user changes his mind
• new government legalisation/company policy company changes
• changes in hardware
• changes in software/upgrades/new versions
• improved operating efficiency/ease of use