Systems software 2: utility software

Utility software performs maintenance, organisation and other housekeeping tasks for a computer system. Utilities provide additional functions that may not be carried out by the operating system itself.

By the end of this worksheet, you should be able to:

• explain the overall purpose of utility software
• explain encryption software and why it is required
• explain fragmentation, defragmentation and their effect on a magnetic hard disk drive
• explain data compression software and why it is required
• select and justify a utility for a scenario
• avoid common misconceptions about interception, storage space and solid-state storage

OCR J277 names three utilities in this section: encryption software, defragmentation and data compression.

1. Purpose of utility software

Utility software helps maintain, monitor, manage or configure a computer system. This work is often called housekeeping. A utility might protect data, reorganise stored data or reduce the size of a file.

The operating system provides the essential environment in which applications and hardware are managed. A utility performs a more focused additional task. Computers often include utilities, but a utility can also be installed separately.

When asked for the general purpose of utility software, do not give only the name of one example. State that it performs maintenance, housekeeping or additional system-management tasks.

2. Three required utilities

Encryption software

Encryption software uses an algorithm and a key to change plaintext into ciphertext. Someone with the correct key can decrypt it. If encrypted data is intercepted or accessed without authorisation, it should be meaningless and cannot be understood without the key. Encryption does not stop interception or copying.

Defragmentation software

Defragmentation software reorganises fragmented files on a magnetic hard disk drive. It moves parts of a file so they are stored consecutively and brings separate areas of free space together. The read/write head then travels a shorter distance and performs fewer separate accesses, so data can be accessed faster. Defragmentation does not create additional storage capacity.

Data compression software

Data compression software encodes data so that a file uses fewer bits. Smaller files require less storage space and can be transferred more quickly because less data must be sent. The software may also decompress a file so it can be used. Lossless compression reconstructs the original data exactly; lossy compression permanently removes some data to achieve a greater size reduction.

3. Encryption: mechanism, purpose and limitation

A complete explanation includes three linked ideas:

1. Mechanism: an algorithm and key change plaintext into ciphertext.
2. Purpose: without the correct key, an unauthorised person should not be able to understand the ciphertext.
3. Limitation: the encrypted data can still be intercepted, copied or deleted.

A vague phrase such as “the file is locked” misses the role of the key and the change to the data. Likewise, saying that encryption stops interception is incorrect.

Encryption can protect stored files and data being transferred. The key must be protected, because an attacker who obtains it may be able to decrypt the data.

4. Fragmentation and defragmentation

On a magnetic hard disk drive, files are added and deleted over time. The available spaces may be too small to hold a new file in one place, so the file is split into fragments stored in separate locations.

Defragmentation software:

1. analyses the disk to find fragmented files
2. moves the fragments of each file together so they are consecutive or contiguous
3. moves separate areas of free space together

The magnetic read/write head then moves a shorter distance and fewer separate locations must be accessed. This reduces access time.

Two common misconceptions:

• Defragmentation rearranges existing data and free space. It does not increase the disk's capacity or create more storage.
• The access-speed explanation depends on a moving read/write head. Solid-state drives have no moving head and do not require this kind of defragmentation.

5. Data compression

Data compression software reduces the number of bits needed to represent a file. This can:

• reduce the storage space required
• reduce the amount of data transmitted
• reduce transfer time when the connection speed is unchanged
• make it easier to attach or download large files

Lossless compression allows the original data to be reconstructed exactly. It is suitable when every bit matters, such as program code or text. Lossy compression permanently removes some data, usually producing a smaller file. It can be suitable for images, sound or video when a reduction in quality is acceptable.

Compression does not automatically change the capacity of a storage device or increase network bandwidth. It reduces the size of the particular file.

Review

Complete this closed-book retrieval routine, then check your answers:

1. Define the general purpose of utility software without naming an example.
2. For encryption, state the mechanism, purpose and limitation.
3. For defragmentation, state what is moved and why access becomes faster.
4. For compression, state what becomes smaller and give two resulting benefits.

Final misconception check:

• encryption does not stop interception
• defragmentation does not create more storage capacity
• magnetic-head movement does not explain performance on an SSD
• compression reduces a file's size, not the capacity of the storage device