The Central Processing Unit CPU And Memory Computer Science Essay

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In a computer motherboard, there are two main components. They are the processor which is also known as the Central Processing Unit (CPU) and memory. These main components play an important role. CPU is an electronic component that is responsible in carrying out and interpreting basic instructions in order to operate the computer. Whereby the memory is consisting numbers of electronic components that contains data waiting to be execute. Every memory location has its own unique address. These addresses are meant for when an instruction is given by a user, the address from that instruction will be copied to the Memory Address Register (MAR) to finds the location in the memory. CPU will then determine whether it is retrieval or a store. Therefore, the CPU and memory are always working closely with each other to operate an instruction in a computer. Between Memory Data Register and memory, transfer will takes place. MDR is a two way register. There are several types of memory that are used to store data and information such as Random Access Memory (RAM), Read Only Memory (ROM), cache, hard disk, flash, tape or cassette and also optical disc.

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The Random Access Memory (RAM) is also known as main memory, is a storage which allows users to read and write data numbers of time in and from the CPU. Usually, RAM will be erased when a computer is being shut down as it is volatile. However, some RAM chips are still able to maintain the data even though there is no electrical power available. As these RAM devices storage format are not limited use as working memory, therefore they are not limited to memory chips and RAM. Long term modern devices or secondary storage such as magnetic media, laser-readable CDs and DVDs can be defined as the forms of RAM. Dynamic RAM (DRAM) and Static RAM (SRAM) are under the RAM category. DRAM uses less electrical power and less heat. The space is smaller too. DRAM is commonly used as it is cheaper. This type of RAM’s volatile must be recharge with power one thousand times per second. Compare to DRAM, the SRAM is higher cost and have faster speed. It is volatile and small amounts of it are often used in the cache memory for high-speed memory access purpose.

Read Only Memory (ROM) refers to memory chips that are used to stored permanent data and instructions. Mostly, data in ROM chips could not be modified and it only allows a user to write data once. That data could be read as many times as the user wishes too once it has been written. ROM is a nonvolatile memory. It is also being used generally compared to other creation of storage devices.

Cache memory holds a responsibility in helping the speed of a computer in storing instructions and data that are being used frequently. Different cache is used in different purposes. For examples, L1 cache is built into a CPU, L2 cache is slower but has a larger capacity and L2 advanced transfer cache is much faster and could be built directly on a CPU chip.

Diagram shows the steps use of cache.

In diagram of the steps use of cache, the tags are the pointer to a location in the main memory. Cache controller enables hardware in checking tags. Cache lines are the connection between storage and cache memory for transferring purpose. Hit ratio is the ratio of hits out of total requests.

As for hard disk, it has a high-capacity of storage compare with a USB flash drive. In a hard disk contains numbers of inflexible and circular platters that are used to store data and information. All components that are in a hard disk are air tightly enclosed with a sealed case that protects it. Characteristics of a hard disk are advertised capacity, platters, read or write heads, cylinders, bytes per second, sectors per track, sectors per drive, revolutions per minute, transfer rate and the access time. A hard disk records data or information in two ways, longitudinal recording and perpendicular recording. A hard disk has tracks on it. Same track on all of the platters are known as cylinder. There are blocks on hard disk, small arc of a track. The sector that looks like pie-shaped part of a platter and the head are meant for reading data on disk when the disk is rotating at a high speed, 4200 till 14000 RPM. Head crash is disk damage once head touches disk surface.

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Step 3

A program requests a disk access, read or write heads will determine the location of the data

Step 2

Small motor will spins when a computer is runningPicture shows a hard disk layout.

Step 4

Head actuator positions read and write head arms over correct location on platters for read or write the data

Step 1

Circuit board control movement of head actuator and a small motor

Picture shows the steps of a hard disk operate.

In markets, flash are cost more than a disk but has a higher speed. When bits of data or information need to be store, a flash would uses hot carrier injection. However, compare to RAM, flash has a slow rewrite time. Generally, more users would go for a flash drive as it is a portable storage device even though the price is higher. The size of a flash is small and light. Therefore, many users will usually put it in a pocket or hang it on a keychain. Flash is a non-volatile memory type. The data and information in a flash drive can be erased and modified. Flash memory is widely used. PDAs, smart phones, digital cameras and audio players such as MP3 have flash memory to store data. Averagely, flash drive able to hold about 500 million characters.

Tape or a cassette is the lowest cost among many storage devices. The physical look of a tape is magnetically coated with plastic ribbon. Even the cost is low; tapes are still capable to store large amounts of data and information. Tapes are offline storage and are mainly being used as backup. It is also has the ability as a disaster recovery. The data are stored in a tape using a sequential access method. This method reads and writes the data that on the tape continuously. For example, a music tape that records songs will be played one after another accordingly in sequence. Tapes are different from hard disk, CDs and DVDs. It is not a direct access which is able to locate data location immediately. There are two types of tape format, linear tape open format and helical scan tape format.

Pictures of linear tape format and helical scan tape format.

Optical disc is one of the portable storage devices. The outlook of an optical disc is flat and round. It is being made with metal, plastic and lacquer. Many computers including laptop have an optical disc drive. Usually, optical disc can be read or read and write. Compact Disc Read-Only Memory (CD-ROM), picture CDs, Compact Disc-Recordable, Compact Disc-Rewriteable and Digital Versatile disc-ROM are the types of optical discs. The data that are stored in a CD-ROM could not be erase or being modify. A CD-ROM is able to holds 650 MB to 1GB. Normally, CD-ROMs are meant for distributing multimedia and complex software purpose. The picture CD stores digital versions of films. It can be modify by using a photo editing software. CD-Rs and CD-RW share a similar characteristic; both of them need to have a drive to transmit data. A CR-R needs a CD recorder or a CD-R drive to help to transfer the data and once the data is transferred, it is inerasable. But a CD-RW will need to have CD-RW software and CD-RW drive to transfer data and the data in the CD-RW can be erased and rewrite it many times. As for DVD-ROM, it is also called digital video disc-ROM. In a DVD-ROM, database, music files, complex software and movies are stored in it. In order to read data that are being stored in a DVD-ROM, a DVD-ROM drive or a DVD player will be needed. The examples of DVD-ROMs are Blue-ray disc that could have a high capacity up to 100 GB and high definition disc (HD-DVD disc) that holds up to 60 GB storage capacity.

In conclusion, each storage devices has its own terms of capacity, access method and characteristics. Some of them are similar to each other but some terms are different from each other. The diagram shows each type of storage device’s access time.

Thus, a device that could store a higher capacity of storage will need more time to be access.

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