2023.3.23 CS笔记

Hardware Part1

1 mark for the device. 1 mark for corresponding reason.
• Device: Server
• Reason: Server processes the requests and authorises traffic // firewall
software on the server authorises traffic // server acts as the proxy
• Device: Switch
• Reason: Switch is connected to all the computers // to share access to
the router on the network

1 mark for each bullet point (max 3):
• receive packets from devices / internet
• find destination of packets using the IP address
• forward packets to the destination
• assign private IP addresses to devices on LAN
• store/update/maintain a routing table
• find most efficient path to destination
• maintain table of MAC and IP addresses
• provides the LAN with a public IP address
• acts as a gateway
• performs protocol conversion
• acts as a firewall

Software Part 2

12.3.4 Program maintenance 软件开发周期- 软件维护

Program maintenance is not like maintaining a piece of equipment by replacing worn out parts. Programs do not wear out, but they might not work correctly in unforeseen circumstances. Logic or run-time errors that require correction may occur from time to time, or users may want to use the program in a different way.

Program maintenance can usually be divided into three categories:

• » Corrective maintenance is used to correct any errors that appear during use, for example trapping a run-time error that had been missed during testing.

• » Perfective maintenance is used to improve the performance of a program during its use, for example improving the speed of response.

• » Adaptive maintenance is used to alter a program so it can perform any new tasks required by the customer, for example working with voice commands as well as keyboard entry.

Structure chart—软件结构图中的要点：

1.实心点代表传递的值类型为Boolean
2.一个值上面的两个箭头：By reference: 传址调用。即将原来地址里的值复制到新地址之后，对新地址进行更改，原来地址中的内容不做更改。