A/AS Level Computer Science for WJEC
Fragmentation and defragmentation Files stored on computer systems can, over time, become fragmented. This means that they are split and stored on different parts of the disc. If a file is fragmented, it takes longer for the disc heads to move between parts of the file, which slows the process of loading it. Defragmentation is the process where files are physically re-arranged on disc so that they are no longer fragmented and the parts of each file are stored together. This improves the speed of accessing data from disc.
Networks
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Unlike magnetic storage devices, SSD uses direct access to data so there would be little point in defragmenting an SSD as there would be no improvement in read times as there’s no physical read head to move. As a result, defragmentation may perform “trim” commands which may slightly improve the speed of future write operations. As SSD is currently made out of NAND based flash memory, which has a limited lifespan, the defragmentation process may shorten its lifespan.
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Most computing systems are connected to some form of network, most commonly the internet. Computers may be connected through wired or wireless links. At its most basic, a computer network is a collection of interconnected computers that have the ability to communicate with one another.
The importance of networking standards
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What underpins all communication is the idea of protocols. No matter what data is being sent or how the various devices in the network are connected, a set of protocols is required to ensure that both the sender and the receiver understand one another.
Types of network
Not every service or task a user wishes to perform will be done on a single computer. Networked computers can share files, offer services (such as email) and communicate with each other. Even when two PCs share a printer, a network is involved. The biggest network in the world is the internet. When services are distributed over a network, you have a distributed system. A distributed system, in essence, is where computers work together by sharing services with one another in order to provide a complete system. In a distributed system, it is important to remember that both processing and data are distributed. Networks differ in size depending on where they are located. At home, you will most likely have a small network. This is referred to as a local area network (LAN). Schools have a bigger network than at home, with many more computers connected together. Even though the size of a school network is large when compared to a home network, it is still referred to as a LAN. Local refers to the computers being near each other geographically rather than the number of computers connected to the network. The internet is a worldwide communications infrastructure, which means that you can access websites, or more specifically web servers, in any country in the world. As the geographical distance between computers on the internet is very great, the internet constitutes a wide area network (WAN). LANs are inherently more secure than WANs. In a LAN setting, all networked devices are likely to be under the control of a small group of network technicians, whereas WANs
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