DNS Server

The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates domain names meaningful for users to the numerical IP addresses needed for the purpose of locating computer services and devices worldwide. By providing a worldwide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet.
An often-used analogy to explain the Domain Name System is that it serves as the phone book for the Internet by translating human-friendly computer hostnames into IP addresses. For example, the domain name www.example.com translates to the addresses 192.0.43.10 (IPv4) and 2620:0:2d0:200::10 (IPv6). Unlike a phone book, the DNS can be quickly updated, allowing a service's location on the network to change without affecting the end users, who continue to use the same host name. Users take advantage of this when they recite meaningful Uniform Resource Locators (URLs) and e-mail addresses without having to know how the computer actually locates the services.
The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain. Authoritative name servers are assigned to be responsible for their particular domains, and in turn can assign other authoritative name servers for their sub-domains. This mechanism has made the DNS distributed and fault tolerant and has helped avoid the need for a single central register to be continually consulted and updated. Additionally, the responsibility for maintaining and updating the master record for the domains is spread among many domain name registrars, who compete for the end-user's, domain-owner's, business. Domains can be moved from registrar to registrar at any time.
The Domain Name System also specifies the technical functionality of this database service. It defines the DNS protocol, a detailed specification of the data structures and communication exchanges used in DNS, as part of the Internet Protocol Suite.
The Internet maintains two principal namespaces, the domain name hierarchy and the Internet Protocol (IP) address spaces. The Domain Name System maintains the domain name hierarchy and provides translation services between it and the address spaces. Internet name servers and a communication protocol implement the Domain Name System. A DNS name server is a server that stores the DNS records for a domain name, such as address (A) records, name server (NS) records, and mail exchanger (MX) records (see also list of DNS record types); a DNS name server responds with answers to queries against its database.

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Simple Present Tense

Formula untuk Simple Present Tense adalah:

Subject + Verb1 + Object + Modifier

Note: jika subject diikuti oleh adjective atau noun, gunakan be: is/am/are. Is digunakan jika subject-nya singular yaitu he, she, it dan noun yang dapat digantikan dengan subject pronoun he, she atau it; Am jika subject-nya I; Sedangkan, are jika subject-nya you, they, atau we.  Subject pronoun I, you, they, we, dan noun yang dapat digantikan dengan I, you, they atau we disebut plural subject.

Contoh:

1. Farmers in Jati Bali grow rice crops twice a year. (Petani-petani di Jati Bali bercocok tanam padi dua kali setahun).
2. Some students usually conduct research on vegetative plant propagations. (Beberapa siswa biasanya melakukan penelitian pada perbanyakan tanaman vegetatif).
3. Transpiration starts to increase at 8 a.m. (Transpirasi mulai meningkat jam 8 pagi).

Note: Pada contoh 1 dan 2 digunakan plural verb karena subject-nya plural, sedangkan pada contoh yang ketiga digunakan singular verb [verb1 + (s atau es)] karena didahului oleh singular subject.

Kapan verb1 ditambahkan huruf s dan kapan ditambahkan huruf es sehingga menjadi singular verb yang benar? Hampir semua singular verb dibentuk dengan menambahkan huruf s diakhir verb1 (i.e. Verb1 + s ). Namun, mengingat jumlah verb sangat banyak, maka yang perlu dipahami/dihafal sekarang adalah kapan kita harus menambahkan es. Ketentuannya adalah jika verb1 berakhiran dengan huruf “o, x, ch, y, th, s,  dan sh” maka Verb1 + es.

Contoh:

Verb1	Verb1 + es	Meaning
go do box watch pinch punch study cry fly try press pass smash brush bath sooth wash	goes does boxes watches pinches punches studies cries flies tries presses passes smashes brushes bathes soothes washes	pergi melakukan/mengerjakan bertinju menonton mencubit memukul belajar menangis terbang mencoba menekan, tindis lulus, meloloskan memukul menyikat mandi menenangkan mencuci

Note:

• Huruf ‘y’ yang didahului oleh konsonan berubah menjadi ‘i’ (Lihat: studies, tries, cries).
• Verb have (mempunyai) berubah secara tidak beraturan menjadi has.

Pertanyaan berikutnya adalah kapan simple present tense digunakan?

Simple present tense digunakan:

1. untuk menyatakan kejadian-kejadian yang terjadi secara reguler (regular happening).

Contoh:

1. The sun rises in the east and sets in the west. (Matahari terbit di timur dan tenggelam di barat).
2. The full moon comes every 30 days. (Purnama datang tiap 30 hari).
3. The planet earth takes 365 days to rotate the sun. (Planet bumi butuh 365 hari untuk mengelilingi matahari).

2. untuk menyatakan kebiasan-kebiasaan yang dilakukan oleh subject kalimat (habitual action); Kebiasaan-kebiasaan tersebut masih berlangsung sampai sekarang dan (mungkin) akan terus berlanjut ke masa yang akan datang (future).

Contoh:

1. My son always goes to school on foot. (Putra saya selalu pergi ke sekolah dengan berjalan kaki).
2. Mr. Bain usually plays badminton every Sunday morning but he did not show up last Sunday. (Mr Bain biasanya main bulutangkis tiap minggu pagi tetapi dia tidak muncul (tidak main) hari Minggu yang lalu).
3. Mr. Budi always drives a car to the office. (Mr. Budi selalu mengendarai mobil ke kantor).

3. Untuk menyatakan argumen atau teori yang sudah diakui kebenarannya.

Contoh:

1. The prices of goods always increase when the good availabilities drop in market. (Harga-harga barang selalu naik ketika ketersedianya di pasar menurun).
2. Solar radiation is required during photosynthesis. (Radiasi surya dibutuhkan selama proses fotosintesis).
3. Twenty-five devided by five is equal to five. (25 dibagi 5 sama dengan 5).

4. Untuk menyatakan/mengekspresikan keadaan atau kondisi seseorang atau sesuatu pada saat sekarang (pada saat diekspresikan). Verbs untuk mengekspresikan seseorang atau sesuatu ini terkait dengan proses/keadaan di dalam otak, terkait dengan perasaan, terkait dengan panca indera,  dan terkait dengan kepemilikan. Verbs seperti ini secara kolektif disebut Stative Verbs. Verbs ini sering kita gunakan atau dengar dalam kehidupan sehari-hari. Jadi, perhatikan dan hafalkan verbs dalam tabel berikut!

Terkait dengan proses/keadaan di dalam otak
know (tahu) believe (percaya) understand (mengerti/paham) imagine (membayangkan) think (berfikir/mengira/kira) recognize (mengenali)	doubt (meragukan) need (memerlukan/butuh) prefer (lebih suka) mean (berarti) forget (melupakan/lupa) remember (mengingat/ingat)
Terkait dengan perasaan
hate (benci) love (cinta)	like (suka) want (menginginkan/ingin)
Terkait dengan panca indera
hear (mendengar) see (melihat) smell (mencium/tercium) appear (muncul)	sound (terdengar) look (melihat/tampak) seem (tampak) taste (merasakan/terasa)
Terkait dengan kepemilikan
have (mempunyai) own (mempunyai)	possess (mempunyai) belong (milik)

Note: Stative verbs bersifat pasif dan tidak digunakan dalam continuous tenses. Tetapi, beberapa stative verbs juga dapat bersifat aktif , bermakna sedikit berbeda dengan stative verbs, dan dalam hal ini, dapat digunakan dalam continuous tenses. Perbedaan penggunaan verbs bersifat pasif dan aktif ini dibahas secara lebih detail di topik  Simple present tense vs present continous tense.

Contoh:

1. I think I know him. (Saya kira/rasa saya tahu dia).
2. I understand English better now. (Saya paham bahasa Inggris dengan lebih baik sekarang).
3. I love you very much. (Saya sangat mencintai kamu).
4. The song sounds good but I cannot catch every single word in it. (Lagu itu terdengar manis tapi saya tidak dapat menangkap satu kata pun dari lagu itu).
5. The snack tastes so delicious. (Camilan itu terasa begitu lezat).
6. I believe you. (Saya percaya kamu).
7. The tragic accident sometimes appears in my mind. (Kecelakaan tragis itu kadang-kadang muncul di benak saya).
8. She has two dogs and one cat. (Dia punya dua anjing dan satu kucing), etc.

5. Untuk menyatakan fakta yang ada sekarang. Penekanannya lebih pada adanya fakta, bukan pada proses terjadinya fakta.Verb yang sering digunakan di sini antara lain: consist of, contain, include, exist, cost, be (i.e: is, am, dan are, atau be jika mengikuti modal auxiliary).

Contoh:

1. She weighs more than 100 kg. She is very fat. (Dia beratnya lebih dari 100 kg. Dia sangat gemuk).
2. I want to buy these shoes. How much do they cost? (Saya mau beli sepatu ini. Berapa harganya?).
3. Cigarettes contain a lot of nicotine and other harmful substances. (Rokok-rokok mengandung banyak nikotin dan zat-zat berbahaya lainnya).

6. Untuk membuat request (permintaan/minta tolong) dan command (perintah).

Contoh:

1. May I borrow your pen, please? (Boleh saya pinjam pulpenmu?).
2. Make teams that consist of 5 people each! (Buatlah tim yang masing-masing terdiri dari 5 orang).

Note: Dalam simple present tense, sering digunakan adverb seperti: always (selalu), often (sering), usually (biasanya), sometimes (kadang-kadang), seldom (jarang), never (tidak pernah). Adverbs ini biasanya ditempatkan diantara subject dan verb. Tetapi jika kalimat menggunakan be, adverb ditempatkan setelah be (Lihat contoh 4). Walaupun disisipi adverb, bentuk verb tidak berubah. Artinya, jika subject-nya singular (orang ketiga tunggal), verbnya tetap singular (Lihat contoh 5). Selain adverbs, simple present tense juga sering disisipi modal auxilliary seperti can (dapat), may (boleh, mungkin), dan must (harus). (Lihat contoh 6). Dan ingat, gunakan plural verb setelah modal auxilliary. Singular verb tidak pernah digunakan setelah modal auxiliary (Lihat contoh 7). Penggunaan modal auxilliary akan dibahas secara khusus pada posting berikutnya.

Contoh :

1. I usually watch Hollywood movies to maintain my English proficiency. (Saya biasanya nonton film-film Hollywood untuk mempertahankan kemampuan bahasa Inggris saya).
2. They always arrive on time. (Mereka selalu tiba tepat waktu).
3. My children sometimes go to Kuta Beach to practice their English. (Anak-anak saya kadang-kadang pergi ke pantai Kuta untuk melatih bahasa Ingggrisnya).
4. He is never late. (Dia tak pernah telat).
5. Because he seldom studies hard, he seldom gets good results. (Karena dia jarang belajar keras, dia jarang dapat nilai bagus).
6. Can I go now? No, you can’t. You must stay here until we finish doing our homework. (Dapat saya pergi sekarang? Tidak. Kamu harus tetap di sini sampai kita selesai mengerjakan PR kita).
7. He must go to see a doctor now. (Dia harus pergi ke dokter sekarang).

Negative Form

Bentuk negatif dari kalimat dalam Simple Present Tense dibuat dengan menambahkan kata bantu ‘do’ atau ‘does’ (tergantung dari subject kalimat)  dan not, seperti terlihat dalam formula berikut,

Subject + (does/do) + not + Verb1 + Object + Modifier

Note: a) Jika kalimat positifnya menggunakan singular verb (i.e. verb1 + s/es), gunakan kata bantu does sebelum not dan jangan lupa untuk merubah singgular verb tersebut menjadi verb1. Does not dapat disingkat doesn’t dan do not dapat disingkat don’t. b) Jika kalimat positifnya menggunakan be (i.e. is, am atau are), kata bantu do atau does tidak diperlukan. Yang perlu dilakukan di sini hanyalah menyisipkan not setelah be, yang masing-masing dapat disingkat menjadi isn’t/ aren’t. Kontraksi am + not adalah ain’t, tetapi jangan gunakan kontraksi ini dalam tulisan/percakapan formal karena sangat tidak formal.

Contoh:

1. The sun does not rise in the west and does not set in the east. (Matahari tidak terbit di barat dan tidak tenggelam di timur).
2. The full moon does not come every 15 days. (Purnama tidak datang tiap 15 hari).
3. The planet earth does not take 400 days to rotate the sun. (Planet bumi tidak butuh 400 hari untuk mengelilingi matahari).
4. My son does not always go to school on foot. (Putraku tidak selalu pergi ke sekolah dengan berjalan kaki).
5. Mr. Bain does not always play badminton every Sunday morning. (Mr Bain tidak selalu main bulutangkis tiap minggu pagi).
6. Mr. Budi does not always drive a car to the office. (Mr. Budi tidak selalu naik mobil ke kantor).
7. I do not believe you. (Saya tidak percaya kamu).
8. I do not understand English better now. (Saya tidak memahami bahasa Inggris dengan lebih baik sekarang).
9. The song does not sound good but I can catch every single word in it. (Lagu itu tidak terdengar manis tapi saya dapat menangkap setiap  kata di lagu itu).
10. The snack does not taste good. (Camilan itu tidak  terasa lezat).
11. I do not love you very much. (Saya tidak sangat cinta kamu).
12. I do not always watch Hollywood movies to maintain my English proficiency. (Saya tidak selalu nonton film-film Hollywood untuk mempertahankan kemampuan bahasa Inggrisku).
13. My children do not always practice their English every Saturday night. (Anak-anakku tidak selalu melatih bahasa Ingggrisnya setiap sabtu malam).
14. He is never late. (Dia tak pernah telat).
15. Although he does not always study hard, he always gets good results. (Walaupun dia tidak selalu belajar keras, dia selalu  memperoleh nilai bagus).

Yes/No Questions

Yes/No Questions untuk Simple Present Tense dibuat dengan menempatkan kata bantu does/do atau be is/am/are sebelum subject. Perhatikan formula berikut:

Does/Do + Subject + Verb1 + Object + Modifier?

Contoh:

1. Do farmers in Jati Bali grow rice crops twice a year? (Apakah petani-petani di Jati Bali bercocok tanam padi dua kali setahun?).
2. Do some students usually conduct research on vegetative plant propagations? (Apakah beberapa siswa biasanya melakukan penelitian pada perbanyakan tanaman vegetatif?).
3. Does transpiration start to increase at 8 a.m? (Apakah transpirasi mulai meningkat jam 8 pagi?).

Pola di atas khusus untuk positive yes/no questions. Cara membuat negative yes/no questions, questions tag, information questions, dan embedded questions dibahas secara detail di topik How to Address Questions.

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Present Continuous Tense & Present Progessive Tense

Formula untuk Present Continuous Tense atau Present Progressive Tense adalah:

Subject +  (is/am/are)  + (Verb1+ing) + Object + Modifier

1. Farmers in Jati Bali are growing rice crops now. (Petani-petani di Jati Bali sedang bercock tanam padi sekarang).
2. Some students are conducting research on vegetative plant propagations. (Beberapa siswa sedang melakukan penelitian pada perbanyakan tanaman vegetatif).
3. Transpiration is starting to increase now. (Transpirasi sedang mulai meningkat sekarang).

Penggunaan Present Continuous Tense

Penggunaan present continuous tense ada 2, yaitu:

1. Present Continuous Tense digunakan untuk menyatakan bahwa subject kalimat sedang melakukan suatu kegiatan. Pada saat dibicarakan (now), kejadian atau aktivitas tersebut sedang berlangsung.

Contoh:

1. We are studying English now. (Kita sedang belajar bahasa Inggris sekarang).
2. She is listening to the music now. (Dia sedang mendengarkan musik itu sekarang).
3. I am discussing English with my colleagues now. (Saya sedang mendiskusikan bahasa Inggris dengan teman-teman kerja saya sekarang).
4. They are playing football now. (Mereka sedang main sepakbola sekarang).
5. James, the gardener, is watering plants now. (James, si tukang kebun, sedang menyirami tanaman sekarang).

2. Present continuous tense juga digunakan untuk menyatakan dua atau lebih aktivitas yang SEDANG berlangsung secara bersamaan. Aktivitas yang sedang berlangsung tersebut biasanya dihubungkan dengan conjunction while dan and.

Contoh:

1. What are your two little sisters doing now? Are they studying? Yes mom, they are both studying. Ririn is studying the present continuous tense while Rini is solving math problems. (little = adik, math problems = soal-soal matematika).
2. Are your parents at home? Yes, they are. My father is reading newspapers in the living room and my mom is cooking in the kitchen.

Negative Form

Bentuk negatif dari kalimat dalam Present Continuous Tense dibuat dengan menambahkan NOT di belakang be (is/am/are), seperti yang terlihat dalam formula berikut:

Subject +  (is/ am/are)  + not + (Verb1+ing) + Object + Modifier

Contoh:

1. We are not studying English now. (Kita tidak sedang belajar bahasa Inggris sekarang).
2. She is not listening to the music now. (Dia tidak sedang mendengarkan musik sekarang).
3. I am not discussing English with my colleagues at the moment. (Saya tidak sedang mendiskusikan bahasa Inggris dengan teman-teman kerjaku sekarang).
4. They are not playing football now. (Mereka tidak sedang main bola sekarang).
5. James, the gardener, is not watering the plants now. (James, si tukang kebun, tidak sedang menyirami tanaman sekarang).
6. I am not writing this note while my wife is not washing clothes. (Saya tidak sedang menulis catatan ini, sementara istri saya sedang mencuci pakaian).

Yes/No Questions

Yes/No Questions untuk Present Continuous Tense dibuat dengan menempatkan be (is/am/are) di depan subject, seperti tampak pada pola berikut:

(Is/Am/Are)  + Subject + (Verb1+ ing) + Object + Modifier

Contoh:

1. Are we studying English at the moment? (Apakah kita sedang belajar bahasa Inggris sekarang?).
2. Is she listening to the music now? (Apakah dia sedang mendengarkan musik sekarang?).
3. Am I discussing English with my colleagues now? (Apakah saya sedang mendiskusikan bahasa Inggris dengan teman-teman kerja saya sekarang?).
4. Are they not playing football now? (Apakah mereka tidak sedang main bola sekarang).
5. Is James, the gardener, not watering the plants now? (Apakah James, si tukang kebun, tidak sedang menyirami tanaman sekarang?).

Modifier of time (Keterangan waktu)

Keterangan waktu untuk kalimat dalam present continuous tense antara lain:

1. now (sekarang)
2. at the moment (sekarang).

Contoh-contoh kalimat yang lain:

1. Be quite, please! She is  studying at the moment. (Tolong, jangan ribut. Dia sedang  sedang belajar sekarang.).
2. Yeyes is watching TV now. (Yeyes sedang menonton TV).
3. I am listening to some pop songs from my CD player. (Saya sedang mendengarkan beberapa lagu pop dari CD player-ku).
4. Don’t eject the diskette from CPU if the diskette indicator is still on. It means that the program is still writing onto the diskette. (Jangan keluarkan disket dari CPU jika lampu indikator disket masih menyala. Itu berarti program masih sedang menulis ke dalam disket).
5. The phone is ringing. Pick it up, please! (Telephon sedang berdering. Tolong angkat teleponnya!).
6. I am writing this note while my wife is washing clothes. (Saya sedang menulis catatan ini, sementara istri saya sedang mencuci pakaian).
7. What are you looking at? (Apa yang sedang kamu perhatikan/pandangi?).

Kenapa harus digunakan verb+ing?

Verb+ing (present participle) digunakan dalam present continuous tense, dan juga dalam tensis-tensis progressive lainnya (i.e. past continuous, perfect continuous, dst). Penggunaan verb+ing ini dimaksudkan untuk menyatakan bahwa aktivitas SEDANG dilakukan atau kejadian SEDANG berlangsung (in progress). Jika  -ing form ditiadakan,  makna SEDANG-nya akan menjadi hilang. Perbedaan ini tampak jelas pada kalimat-kalimat pasif berikut:

• The plants are being watered by the gardener now. (Tanaman-tanaman itu SEDANG disiram oleh tukang kebun sekarang).
• The plants are watered by the gardener everyday. (Tanaman-tanaman itu disiram oleh tukang kebun tiap hari).

• The white board is being erased by Andi. (Papan tulis SEDANG dihapus oleh Andi).
• Sometimes, the white board is erased by Andi. (Kadang-kadang papan tulis dihapus oleh Andi).

• The bad boy is being interrogated by his father. (Anak nakal itu SEDANG dinterogasi oleh bapaknya).
• The bad boy is always interrogated by his father. (Anak nakal itu selalu dinterogasi oleh bapaknya).

Sekarang, coba anda rubah kalimat-kalimat pasif di atas menjadi kalimat aktif. Remember: makna SEDANG-nya jangan sampai hilang!

Cara-cara merubah kalimat pasif menjadi kalimat aktif, dan sebaliknya, dari kalimat aktif menjadi kalimat pasif dapat dibaca di topik: Active dan Passive Voice.

Present Continuous vs Simple present tense

Untuk memahami perbedaan penggunaan simple present tense dengan present continuous tense, silakan baca topik : Simple present tense vs Present Continuous tense. Kemudian, setelah mengerjakan Practice test 6 pemahaman anda tentang perbedaan penggunaan kedua tensis ini akan menjadi lebih sempurna.

Penggunaan pola present continuous tense untuk menyatakan aktivitas future time?

Pertama-tama perhatikan keempat contoh kalimat berikut:

1. We are not studying English tomorrow. (Kita tidak akan belajar bahasa Inggris besok).
2. I am not leaving for Bali next month. (Saya tidak akan pergi ke Bali bulan depan).
3. They are not playing for the tournament next week.  (Mereka tidak akan bertanding minggu depan).
4. She is coming home next Monday. (Dia akan pulang Senin depan).

Apakah keempat kalimat di atas benar? Apakah pola present continuous tense dapat digunakan untuk menyatakan kejadian atau aktivitas yang akan berlangsung di masa mendatang (future time)?

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DNS ( Domain Name System )

The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates domain names meaningful for users to the numerical IP addresses needed for the purpose of locating computer services and devices worldwide. By providing a worldwide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet.
An often-used analogy to explain the Domain Name System is that it serves as the phone book for the Internet by translating human-friendly computer hostnames into IP addresses. For example, the domain name www.example.com translates to the addresses 192.0.43.10 (IPv4) and 2620:0:2d0:200::10 (IPv6). Unlike a phone book, the DNS can be quickly updated, allowing a service's location on the network to change without affecting the end users, who continue to use the same host name. Users take advantage of this when they recite meaningful Uniform Resource Locators (URLs) and e-mail addresses without having to know how the computer actually locates the services.
The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain. Authoritative name servers are assigned to be responsible for their particular domains, and in turn can assign other authoritative name servers for their sub-domains. This mechanism has made the DNS distributed and fault tolerant and has helped avoid the need for a single central register to be continually consulted and updated. Additionally, the responsibility for maintaining and updating the master record for the domains is spread among many domain name registrars, who compete for the end-user's, domain-owner's, business. Domains can be moved from registrar to registrar at any time.
The Domain Name System also specifies the technical functionality of this database service. It defines the DNS protocol, a detailed specification of the data structures and communication exchanges used in DNS, as part of the Internet Protocol Suite.
The Internet maintains two principal namespaces, the domain name hierarchy and the Internet Protocol (IP) address spaces. The Domain Name System maintains the domain name hierarchy and provides translation services between it and the address spaces. Internet name servers and a communication protocol implement the Domain Name System. A DNS name server is a server that stores the DNS records for a domain name, such as address (A) records, name server (NS) records, and mail exchanger (MX) records (see also list of DNS record types); a DNS name server responds with answers to queries against its database.

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BACKUP

   In information technology, a backup, or the process of backing up, refers to the copying and archiving of computer data so it may be used to restore the original after a data loss event. The verb form is to back up in two words, whereas the noun is backup.
    Backups have two distinct purposes. The primary purpose is to recover data after its loss, be it by data deletion or corruption. Data loss can be a common experience of computer users. A 2008 survey found that 66% of respondents had lost files on their home PC. The secondary purpose of backups is to recover data from an earlier time, according to a user-defined data retention policy, typically configured within a backup application for how long copies of data are required. Though backups popularly represent a simple form of disaster recovery, and should be part of a disaster recovery plan, by themselves, backups should not alone be considered disaster recovery. One reason for this is that not all backup systems or backup applications are able to reconstitute a computer system or other complex configurations such as a computer cluster, active directory servers, or a database server, by restoring only data from a backup.
   Since a backup system contains at least one copy of all data worth saving, the data storage requirements can be significant. Organizing this storage space and managing the backup process can be complicated undertaking. A data repository model can be used to provide structure to the storage. Nowadays, there are many different types of data storage devices that are useful for making backups. There are also many different ways in which these devices can be arranged to provide geographic redundancy, data security, and portability.
   Before data is sent to its storage location, it is selected, extracted, and manipulated. Many different techniques have been developed to optimize the backup procedure. These include optimizations for dealing with open files and live data sources as well as compression, encryption, and de-duplication, among others. Every backup scheme should include dry runs that validate the reliability of the data being backed up. It is important to recognize the limitations and human factors involved in any backup scheme.

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