Comparison between CD and DVD, Cache Memory and External Memory Devices

Comparison between CD and DVD:

• Small dots are used to represent the data on CDs.
• The use of a more concentrated laser beam distinguishes DVD from CD. This enables it to read incredibly tiny dots. The smaller dot size allows us to store more info on DVD.
• In contrast to DVD, which can store 4.7 Gigabytes of data on a single layer disc and 8.5 Gigabytes on a twin layer disc, CD can store 640–700 Megabytes of data on a single disc.
• Compared to DVD, CD is slimmer.
• Cheaper than DVD is CD.

Formatting:

The disk surface needs to be magnetically mapped before a computer can use it to store data so that it can navigate to a specific location without first looking through data. The disk drive forms a series of magnetic concentric circles known as tracks while formatting a disk. From the outermost circle to the innermost circle, the tracks are numbered.

Sector:

Each track on a disk is additionally divided into smaller pieces known as sectors. The smallest unit that a disk drive can operate with is a sector.

Working mechanism of CD:

The surface of the CD is covered in land and a pit, which is how the CD functions. Pit stands for binary 0, and land for binary 1. A beam of light is emitted during the CD reading process, strikes the CD's surface, and is reflected. A lens in the CD drive records the reflection. To determine 1 and 0, the difference in reflection from the land and the pit is found. The pit is truly amorphous, while the land is in a crystalline state. In comparison to CD, the size of the land and pit is less in DVD.

Cache memory:

The data and instructions that the CPU most recently called from RAM are temporarily stored in cache memory. It is a kind of extremely quick memory that boosts a computer's performance. It equalizes the variance in RAM and CPU running speeds. It is five to ten times as quick as RAM. It functions as a bridge between the CPU and memory, saving only the most often and most recently used information.

The CPU first checks to determine if the data is in cache memory when a program is running and it has to read data or a program instruction from RAM. If the data is missing, the CPU loads a copy of the data into cache memory while concurrently reading the data from RAM into registers. The CPU finds the same data in memory the next time it needs it, saving time from having to load the data from RAM. Cache hits occur when the CPU locates the necessary data or program instruction in the cache; cache misses occur when the CPU fails to locate the necessary data or program instruction in the cache. The ratio of hit and miss in a present computer is 9:1. Cache is further divided into L1 Cache and L2 Cache. L1 Cache contains more frequently required data compared to L2 Cache.

External memory devices:

• Zip disk: It is a magnetic memory. It is a floppy disk modification. It features 100MB and 250MB of storage space. It needs a Zip disk drive to function.
• Jaz disk: It is also a magnetic memory. It features a 2 GB storage capacity. Additionally, a separate Jaz disk drive is necessary for its operation.
• Super disk: A magnetic memory is also a super disk. It contains 120MB of storage space. Super disk drive is necessary for its operation. A super disk drive can accommodate both floppy and super disk media.
• Pen drive: Flash memory is a pen drive. The memory is a semiconductor. It is mostly utilized for data transport. In comparison to magnetic memory, it reads and writes data more quickly.
• Portable hard disk: The hard drive is magnetic. The USB port on the computer can be used to connect to it. Furthermore, it is a plug-and-play gadget. The backup is primarily stored there. It offers storage space ranging from a few GB to TB.
• SD Card: Secured Digital Card is referred to as an SD card. Its small size enables the storage feature portable in many different gadgets, including cameras, cellphones, tablets, and other electronic devices. It has the capacity to hold documents, photographs, music, and videos. Its price and capacity change over time.

Reference:

Ghishing, Er.Ashim. Computer Science. Kathmandu, Nepal: Benchmark , 2008.