Mark Scheme: J277/01 Computer Systems (Version G)

QAnswer/Indicative ContentMarks
1(a) Program Counter (PC): Holds the address of the next instruction to be fetched from memory. (1) Increments by 1 after each fetch. (1)
Accumulator (ACC): Stores the results of calculations and logic operations performed by the ALU. (1) Acts as a temporary holding area for data being processed. (1)
+1 mark for accurate context of Von Neumann.
5
1(b) Virtual Memory: A section of the secondary storage (HDD/SSD) that is used as temporary RAM when the physical RAM is full. (1) Data not currently in use is swapped out to disk. (1)
Thrashing: When the system spends more time swapping data between RAM and Disk than actually executing instructions. (1) Results in a severe drop in system responsiveness/performance. (1)
4
1(c) Justification (e.g., Magnetic Hard Drive):
- High capacity (500GB is easily/cheaply available on HDD). (1)
- Low cost per GB compared to SSD/Cloud. (1)
- Reliable for long-term archiving (not prone to degradation like some optical media). (1)
Comparison (e.g., Optical/Cloud):
- Optical is too small (e.g., 4.7GB/25GB) requiring 20-100 disks. (1)
- Cloud requires a persistent high-speed connection for large uploads/downloads. (1)
- SSD is significantly more expensive for high-capacity backup. (1)
6
2(a) LAN: Covers a small geographical area (e.g. school/office). (1) Uses owned hardware. (1)
WAN: Covers a large geographical area (e.g. across cities/countries). (1) Uses third-party hardware (e.g. leased lines/satellites). (1)
Examples: LAN (Home Wi-Fi), WAN (The Internet). (1)
5
2(b) Factors (Max 5 marks):
- Bandwidth: The amount of data that can be transmitted in a given time. (2)
- Number of users: More users sharing bandwidth slows down transmission. (2)
- Interference: Physical barriers or electromagnetic noise (e.g. thick walls). (2)
- Type of transmission media: Fiber optic is faster than copper/Wi-Fi. (2)
- Network topology: Mesh can be more efficient than Star in high-traffic. (2)
5
3(a) Hosting is when a business (the host) provides server space for a website. (1) This allows the website to be accessible 24/7 on the internet. (1) 2
3(b) The Cloud refers to servers accessed over the internet (1) and the software and databases that run on those servers. (1)
Benefit: Files can be accessed from any device with an internet connection. (1) / Scalability / Reduced local storage costs.
3
3(c) The Web Client (browser) sends a request (1) using HTTP/HTTPS (1) to the Web Server's IP address. (1)
The Web Server processes the request (1) and sends back the HTML/CSS/JS files to the client to be rendered. (1)
5
4(a) FTP: File Transfer Protocol. Used to send/receive files between computers. (2)
POP: Post Office Protocol. Used to download emails from a server and delete them from the server once downloaded. (2)
IMAP: Internet Message Access Protocol. Used to access emails on a server; keeps them synced across devices. (3)
SMTP: Simple Mail Transfer Protocol. Used to send/transfer emails from a client to a server or between servers. (3)
10
4(b) Layers: Dividing the complex task of network communication into smaller, self-contained sub-tasks. (2)
Advantage: Developers can focus on one layer without worrying about how others work. (1) Interoperability between different manufacturers. (1) Changes in one layer don't break others. (1)
5
5(a) DoS: Flooding a server with useless traffic (1) to make it crash or become unavailable to legitimate users. (2)
Data Interception: Using packet sniffers (1) to capture data as it travels across a network (1) and reading sensitive information if not encrypted. (2)
7
5(b) Methods (1 mark each, max 8):
- Anti-malware software (1)
- Firewalls (1)
- Penetration testing (1)
- User access levels (1)
- Physical security (locks/cameras) (1)
- Strong passwords (1)
- Encryption (1)
- Staff training (1)
8
6(a) Memory Management: Allocates RAM to running processes (1) and prevents one process from accessing another's memory. (1)
User/File Management: Handles login/authentication (1), sets access permissions (1), and manages the file hierarchy/storage on disk. (2)
6
6(b) Utility software performs specific maintenance/housekeeping tasks. (2)
Example: Defragmentation, compression, backup, disk repair. (2)
4
7(a) Open Source: Source code is free to view/edit. (1) Benefit: Highly customisable/Free. (1)
Proprietary: Compiled code, source not available. (1) Benefit: Professional support/Guarantee. (1)
4
7(b) The Computer Misuse Act 1990. (1) 1