NETWORK

Network Administrator Interview Questions

• What is DNS?

Domain name system/server is used to translate the IP address into the hostname and hostname into the IP address. DNS is mostly used on the internet and the networks.

• What is DHCP?

Dynamic host configuration protocol is used to dynamically assign the IP address to the networked computers and devices. DHCP is a network protocol that automatically assigns static and dynamic IP addresses from its own range.

• What is a Router?

Router is the most important network device that is used to connect two logically and physically different networks. Router defines the short possible route for the data to reach its destination. A router works with built-in intelligent software known as routing table, which helps to determine the route between the two networks.

• What is Gateway?

A gateway is software or a hardware that is used to connect the local area network with the internet. A gateway is a network entrance point and a router usually works as a gateway.

• What is WLAN?

WLAN or Wireless local area network is simply a type of network that doesn’t use wired Ethernet connections for networking. WLAN uses wireless network devices such as wireless routers etc.

• What is Subnet Mask?

A subnet mask is used to determine the number of networks and the number of host computers. Every class of the IP address uses the different range of the subnet mask. Subnet masks allow the IP based networks to be divided into the sub networks for performance and security purposes.

• What is a MAC Address?

MAC address or Media Access control is a unique identifier of a computer device. The MAC address is provided by the manufacturer of the device. MAC addresses are 12 digital hexadecimal numbers.

• What is an IP Address?

An IP address is a unique identifier of a computer or network device on the local area network, WAN or on internet. Every host computer on the internet must have a unique IP address. IP addresses on the internet are usually assigned by the local ISPs to which users are connected.

• What is Wifi?

Wi Fi or wireless fidelity is a base band network technology that is used for the wireless data communication.

• What is WiMax?

Wi Fi is a next form of the Wi fi. Wi max is a very high speed broadband network technology that is designed for the corporate offices, roaming and home users.
Name the Seven Layers of OSI Model
The seven layers of the OSI are Application, Presentation, Sessions, Transport, Network, Data Link and Physical layer.

• What is LDAP?

Lightweight Directory Access Protocol is used to access the directory services from the Active directory in Windows operation systems.
What are the standard port numbers for SMTP, POP3, IMAP4, RPC, LDAP, and FTP?
SMTP – 25, POP3 – 110, IMAP4 – 143, RPC – 135, LDAP, FTP-21, HTTP-80

• What is IPv6?

IP V6 is a next generation protocol that is used as an expansion of DNS.

• What is UDP?

UDP or user datagram protocol is a connectionless protocol that is used to transfer the data without any error handling.

• What is Firewall?

A firewall is usually a software program that is installed on the network server or gateway. The purpose of the firewall is to protect the network resources from the intruders and unauthorized persons.

• What is Virtual Private Network (VPN) and how does it work?

VPN or virtual private network is used to connect two networks by means internet. VPN uses PPTP (point to point tunneling protocol) and other security procedures to make a secure tunnel on internet.
Define VOIP
VOIP or voice over internet protocol is a technology that uses IP based networks such as internet or private networks to transmit the voice communication.
Define Bluetooth Technology
Bluetooth is a short range wireless technology that uses radio waves for communication. Many mobile phones, laptops, MP3 players have built in features of the Bluetooth.

• What is a RAS server?

RAS or remote access server allows you to remote dial in through the desktop computers, laptops and GSM mobile phones.

• What’s a Frame Relay?

Frame relay is high speed data communication technology that operates at the physical and data link layers of the OSI model. Frame relay uses frames for data transmission in a network.

Networking Interview Questions and Answers :

1. 1.What is an Object server?

With an object server, the Client/Server application is written as a set of communicating objects. Client object communicate with server objects using an Object Request Broker (ORB). The client invokes a method on a remote object. The ORB locates an instance of that object server class, invokes the requested method and returns the results to the client object. Server objects must provide support for concurrency and sharing. The ORB brings it all together.

1. 2. What is a Transaction server?

With a transaction server, the client invokes remote procedures that reside on the server with an SQL database engine. These remote procedures on the server execute a group of SQL statements. The network exchange consists of a single request/reply message. The SQL statements either all succeed or fail as a unit.

1. 3. What is a Database Server?

With a database server, the client passes SQL requests as messages to the database server. The results of each SQL command are returned over the network. The server uses its own processing power to find the request data instead of passing all the records back to the client and then getting it find its own data. The result is a much more efficient use of distributed processing power. It is also known as SQL engine.

1. 4. What are the most typical functional units of the Client/Server applications?

• User interface
• Business Logic and
• Shared data.

1. 5. What are all the Extended services provided by the OS?

• Ubiquitous communications
• Network OS extension
• Binary large objects (BLOBs)
• Global directories and Network yellow pages
• Authentication and Authorization services
• System management
• Network time
• Database and transaction services
• Internet services
• Object- oriented services

1. 6. What are Triggers and Rules?

Triggers are special user defined actions usually in the form of stored procedures, that are automatically invoked by the server based on data related events. It can perform complex actions and can use the full power of procedural languages.
A rule is a special type of trigger that is used to perform simple checks on data.

1. 7. What is meant by Transparency?

Transparency really means hiding the network and its servers from the users and even the application programmers.

1. 8. What are TP-Lite and TP-Heavy Monitors?

TP-Lite is simply the integration of TP Monitor functions in the database engines. TP-Heavy are TP Monitors which supports the Client/Server architecture and allow PC to initiate some very complex multiserver transaction from the desktop.

1. 9. What are the two types of OLTP?

TP lite, based on stored procedures. TP heavy, based on the TP monitors.

1. 10. What is a Web server?

This new model of Client/Server consists of thin, protable, "universal" clients that talk to superfat servers. In the simplet form, a web server returns documents when clients ask for them by name. The clients and server communicate using an RPC-like protocol called HTTP.

1. 11. What are Super servers?

These are fully-loaded machines which includes multiprocessors, high-speed disk arrays for intervive I/O and fault tolerant features.

1. 12. What is a TP Monitor?

There is no commonly accepted definition for a TP monitor. According to Jeri Edwards' a TP Monitor is "an OS for transaction processing".

1. 13. TP Monitor does mainly two things extremely well. They are Process management and Transaction management.?

They were originally introduced to run classes of applications that could service hundreds and sometimes thousands of clients. TP Monitors provide an OS - on top of existing OS - that connects in real time these thousands of humans with a pool of shared server processes.

1. 14. What is meant by Asymmetrical protocols?

There is a many-to-one relationship between clients and server. Clients always initiate the dialog by requesting a service. Servers are passively awaiting for requests from clients.

1. 15. What are the types of Transparencies?

The types of transparencies the NOS middleware is expected to provide are:-
• Location transparency
• Namespace transparency
• Logon transparency
• Replication transparency
• Local/Remote access transparency
• Distributed time transparency
• Failure transparency and
• Administration transparency.

1. 16. What is the difference between trigger and rule?

The triggers are called implicitly by database generated events, while stored procedures are called explicitly by client applications.

1. 17. What are called Transactions?

The grouped SQL statements are called Transactions (or) A transaction is a collection of actions embused with ACID properties.

1. 18. What are the building blocks of Client/Server?

• The client
• The server and
• Middleware.

1. 19. Explain the building blocks of Client/Server?

The client side building block runs the client side of the application.
The server side building block runs the server side of the application.

1. 20. The middleware buliding block runs on both the client and server sides of an application. It is broken into three categories:-

• Transport stack
• Network OS
• Service-specific middleware.

1. 21. What are all the Base services provided by the OS?

• Task preemption
• Task priority
• Semaphores
• Interprocess communications (IPC)
• Local/Remote Interprocess communication
• Threads
• Intertask protection
• Multiuser
• High performance file system
• Efficient memory management and
• Dynamically linked Run-time extensions.

1. 22. What are the roles of SQL?

• SQL is an interactive query language for ad hoc database queries.
• SQL is a database programming language.
• SQL is a data definition and data administration language.
• SQL is the language of networked database servers
• SQL helps protect the data in a multi-user networked environment.
• Because of these multifacted roles it plays, physicists might call SQL as "The grand unified theory of database".

1. 23. What is Structured Query Langauge (SQL)?

SQL is a powerful set-oriented language which was developed by IBM research for the databases that adhere to the relational model. It consists of a short list of powerful, yet highly flexible, commands that can be used to manipulate information collected in tables. Through SQL, we can manipulate and control sets of records at a time.

1. 24. What are the characteristics of Client/Server?

• Service
• Shared resources
• Asymmentrical protocols
• Transparency of location
• Mix-and-match
• Message based exchanges
• Encapsulation of services
• Scalability
• Integrity
Client/Server computing is the ultimate "Open platform". It gives the freedom to mix-and-match components of almost any level. Clients and servers are loosely coupled systems that interact through a message-passing mechanism.

• 25. What is Remote Procedure Call (RPC)?

RPC hides the intricacies of the network by using the ordinary procedure call mechanism familiar to every programmer. A client process calls a function on a remote server and suspends itself until it gets back the results. Parameters are passed like in any ordinary procedure. The RPC, like an ordinary procedure, is synchoronous. The process that issues the call waits until it gets the results.
Under the covers, the RPC run-time software collects values for the parameters, forms a message, and sends it to the remote server. The server receives the request, unpack the parameters, calls the procedures, and sends the reply back to the client. It is a telephone-like metaphor.

1. 26. What are the main components of Transaction-based Systems?

• Resource Manager
• Transaction Manager and
• Application Program.

1. 27. What are the three types of SQL database server architecture?

• Process-per-client Architecture. (Example: Oracle 6, Informix )
• Multithreaded Architecture. (Example: Sybase, SQL server)
• Hybrid Architecture (Example: Oracle 7)

1. 28. What are the Classification of clients?

Non-GUI clients - Two types are:-
1. Non-GUI clients that do not need multi-tasking
(Example: Automatic Teller Machines (ATM), Cell phone)
2. Non-GUI clients that need multi-tasking
(Example: ROBOTs)
GUI clients
OOUI clients

1. 29. What are called Non-GUI clients, GUI Clients and OOUI Clients?

Non-GUI Client: These are applications, generate server requests with a minimal amount of human interaction.
GUI Clients: These are applicatoins, where occassional requests to the server result from a human interacting with a GUI
(Example: Windows 3.x, NT 3.5)
OOUI clients : These are applications, which are highly-iconic, object-oriented user interface that provides seamless access to information in very visual formats.
(Example: MAC OS, Windows 95, NT 4.0)

1. 30. What is Message Oriented Middleware (MOM)?

MOM allows general purpose messages to be exchanged in a Client/Server system using message queues. Applications communicate over networks by simply putting messages in the queues and getting messages from queues. It typically provides a very simple high level APIs to its services.
MOM's messaging and queuing allow clients and servers to communicate across a network without being linked by a private, dedicated, logical connection. The clients and server can run at different times. It is a post-office like metaphor.

1. 31. What is meant by Middleware?

Middleware is a distributed software needed to support interaction between clients and servers. In short, it is the software that is in the middle of the Client/Server systems and it acts as a bridge between the clients and servers. It starts with the API set on the client side that is used to invoke a service and it covers the transmission of the request over the network and the resulting response.
It neither includes the software that provides the actual service - that is in the servers domain nor the user interface or the application login - that's in clients domain.

1. 32. What are the functions of the typical server program?

It waits for client-initiated requests. Executes many requests at the same time. Takes care of VIP clients first. Initiates and runs background task activity. Keeps running. Grown bigger and faster.

1. 33. What is meant by Symmentric Multiprocessing (SMP)?

It treats all processors as equal. Any processor can do the work of any other processor. Applications are divided into threads that can run concurrently on any available processor. Any processor in the pool can run the OS kernel and execute user-written threads.

1. 34. What are Service-specific middleware?

It is needed to accomplish a particular Client/Server type of services which includes:-
• Database specific middleware
• OLTP specific middleware
• Groupware specific middleware
• Object specific middleware
• Internet specific middleware and
• System management specific middleware.

1. 35. What are General Middleware?

It includes the communication stacks, distributed directories, authentication services, network time, RPC, Queuing services along with the network OS extensions such as the distributed file and print services.

1. 36. What is meant by Asymmetric Multiprocessing (AMP)?

It imposses hierarchy and a division of labour among processors. Only one designated processor, the master, controls (in a tightly coupled arrangement) slave processors dedicated to specific functions.

1. 37. What is OLTP?

In the transaction server, the client component usually includes GUI and the server components usually consists of SQL transactions against a database. These applications are called OLTP (Online Transaction Processing) OLTP Applications typically,
Receive a fixed set of inputs from remote clients. Perform multiple pre-compiled SQL comments against a local database. Commit the work and Return a fixed set of results.

1. 38. What is meant by 3-Tier architecture?

In 3-tier Client/Server systems, the application logic (or process) lives in the middle tier and it is separated from the data and the user interface. In theory, the 3-tier Client/Server systems are more scalable, robust and flexible.
Example: TP monitor, Web.
39. What is meant by 2-Tier architecture?
In 2-tier Client/Server systems, the application logic is either burried inside the user interface on the client or within the database on the server.
Example: File servers and Database servers with stored procedures.
40. What is Load balancing?
If the number of incoming clients requests exceeds the number of processes in a server class, the TP Monitor may dynamically start new ones and this is called Load balancing.
41. What are called Fat clients and Fat servers?
If the bulk of the application runs on the Client side, then it is Fat clients. It is used for decision support and personal software.
If the bulk of the application runs on the Server side, then it is Fat servers. It tries to minimize network interchanges by creating more abstract levels of services.

1. 42. What is meant by Horizontal scaling and Vertical scaling?

Horizontal scaling means adding or removing client workstations with only a slight performance impact. Vertical scaling means migrating to a larger and faster server machine or multiservers.

1. 43. What is Groupware server?

Groupware addresses the management of semi-structured information such as text, image, mail, bulletin boards and the flow of work. These Client/Server systems have people in direct contact with other people.

1. 44. What are the two broad classes of middleware?

• General middleware
• Service-specific middleware.

1. 45. What are the types of Servers?

• File servers
• Database servers Transaction servers Groupware servers
• Object servers Web servers.
46. What is a File server?
File servers are useful for sharing files across a network. With a file server, the client passes requests for file records over nerwork to file server.

1. 47. What are the five major technologies that can be used to create Client/Server applications?

• Database Servers
• TP Monitors
• Groupware
• Distributed Objects
• Intranets.

1. 48. What is Client/Server?

Clients and Servers are separate logical entities that work together over a network to accomplish a task. Many systems with very different architectures that are connected together are also called Client/Server.

1. 49. List out the benefits obtained by using the Client/Server oriented TP Monitors?

• Client/Server applications development framework.
• Firewalls of protection.
• High availability.
• Load balancing.
• MOM integration.
• Scalability of functions.
• Reduced system cost.

1. 50. What are the services provided by the Operating System?

Extended services - These are add-on modular software components that are layered on top of base service.

• Network engineer interview questions

• OSPF

• Describe OSPF in your own words.
• OSPF areas, the purpose of having each of them
• Types of OSPF LSA, the purpose of each LSA type
• What exact LSA type you can see in different areas
• How OSPF establishes neighboor relation, what the stages are
• If OSPF router is stucked in each stage what the problem is and how to troubleshoot it
• OSPF hierarchy in the single or multi areas. Cool OSPF behavior in broadcast and nonbroadcast
• Draw the diagram of typical OSPF network and explain generally how it works, DR, BDR, election, ASBR, ABR, route redistribution and summarization

• STP

• How it works and the purpose
• Diff types (SSTP, MSTP, RSTP) Cisco - PVST/PVST+
• root election
• Diff. port stages and timing for convergence
• Draw the typical diagram and explain how diff types of STP work
• What ports are blocking or forwarding
• How it works if there are topology changes

• ACLs

• What are they
• Diff types
• Write an example if you want to allow and to deny…
• Well-known port numbers (DNS - 53 and etc…)

• QOS

• What is that
• What is the diff b/w L2 and L3 QoS
• How it works

• Network:

• Draw the typical network diagram you have to deal with
• explain how it works
• What part of it you are responsible
• firewall, what is that, how it works, how it is diff from ACLs
• What problems with the network you had had and how you solved it.
• What are the ways to troubleshoot the network, techniques, commands
• network security, ways to achieve it

• Switching:

• VLANs
• STP
• How a L2 switch works with broadcast, unicast, multicast, known/unknown traffic
• VRRP, GLBP
• port monitoring and mirroring
• L3 switch, how it works
• PIM sparse and dense modes

Windows admin interview questions

1. Describe how the DHCP lease is obtained. It’s a four-step process consisting of (a) IP request, (b) IP offer, © IP selection and (d) acknowledgement.

2. I can’t seem to access the Internet, don’t have any access to the corporate network and on ipconfig my address is 169.254.*.*. What happened? The 169.254.*.* netmask is assigned to Windows machines running 98/2000/XP if the DHCP server is not available. The name for the technology is APIPA (Automatic Private Internet Protocol Addressing).

3. We’ve installed a new Windows-based DHCP server, however, the users do not seem to be getting DHCP leases off of it. The server must be authorized first with the Active Directory.

4. How can you force the client to give up the dhcp lease if you have access to the client PC? ipconfig /release

5. What authentication options do Windows 2000 Servers have for remote clients? PAP, SPAP, CHAP, MS-CHAP and EAP.

6. What are the networking protocol options for the Windows clients if for some reason you do not want to use TCP/IP? NWLink (Novell), NetBEUI, AppleTalk (Apple).

7. What is data link layer in the OSI reference model responsible for? Data link layer is located above the physical layer, but below the network layer. Taking raw data bits and packaging them into frames. The network layer will be responsible for addressing the frames, while the physical layer is reponsible for retrieving and sending raw data bits.

8. What is binding order? The order by which the network protocols are used for client-server communications. The most frequently used protocols should be at the top.

9. How do cryptography-based keys ensure the validity of data transferred across the network? Each IP packet is assigned a checksum, so if the checksums do not match on both receiving and transmitting ends, the data was modified or corrupted.

10. Should we deploy IPSEC-based security or certificate-based security? They are really two different technologies. IPSec secures the TCP/IP communication and protects the integrity of the packets. Certificate-based security ensures the validity of authenticated clients and servers.

11. What is LMHOSTS file? It’s a file stored on a host machine that is used to resolve NetBIOS to specific IP addresses.

12. What’s the difference between forward lookup and reverse lookup in DNS? Forward lookup is name-to-address, the reverse lookup is address-to-name.

13. How can you recover a file encrypted using EFS? Use the domain recovery agent.



Network engineer/architect interview questions

1. Explain how traceroute, ping, and tcpdump work and what they are used for?
2. Describe a case where you have used these tools to troubleshoot.
3. What is the last major networking problem you troubleshot and solved on your own in the last year?
4. What LAN analyzer tools are you familiar with and describe how you use them to troubleshoot and on what media and network types.
5. Explain the contents of a routing table (default route, next hop, etc.)
6. What routing protocols have you configured?
7. Describe the commands to set up a route.
8. What routing problems have you troubleshot?
9. How do you display a routing table on a Cisco? On a host?
10. How do you use a routing table and for what?
11. What is a route flap?
12. What is a metric?
13. When do you use BGP, IGRP, OSPF, Static Routes?
14. What do you see as current networking security issues (e.g. NFS mounting, spoofing, one time passwords, etc.)?
15. Describe a routing filter and what it does.
16. Describe an access list and what it does.
17. What is a network management system?
18. Describe how SNMP works.
19. Describe the working environment you are currently in, e.g. frequent interruptions, frequent priority shifting, team or individual.
20. What do you use to write documentation? Editor? Mail reader?
21. What platform (s) do you currently work on at your desk?
22. How do you manage multiple concurrent high level projects?
23. Describe a recent short term stressful situation and how you managed it.
24. How do you manage a long term demanding stressful work environment?
25. Have you worked in an assignment based environment, e.g. work request/trouble ticket system, and if so, describe that environment.
26. Describe what network statistics or measurement tools you are familiar with and how you have used them.
27. Describe what a VPN is and how it works.
28. Describe how VoIP works.
29. Describe methods of QoS.
30. How does ToS bit work?

CCNA/Cisco admin interview questions

1. You need to retrieve a file from the file server for your word processing application, which layer of the OSI model is responsible for this function?
1. Presentation layer
2. Application layer
3. Session layer
4. Transport layer
5. Datalink layer
2. You are working in a word processing program, which is run from the file server. Your data comes back to you in an unintelligible manner. Which layer of the OSI model would you investigate?
1. Application layer
2. Presentation layer
3. Session layer
4. Network layer
5. Datalink layer
3. The IEEE subdivided the datalink layer to provide for environments that need connectionless or connection-oriented services. What are the two layers called?
1. Physical
2. MAC
3. LLC
4. Session
5. IP
4. You are working with graphic translations. Which layer of the OSI model is responsible for code formatting and conversion and graphic standards.
1. Network layer
2. Session layer
3. Transport layer
4. Presentation layer
5. Which is the best definition of encapsulation?
1. Each layer of the OSI model uses encryption to put the PDU from the upper layer into its data field. It adds header and trailer information that is available to its counterpart on the system that will receive it.
2. Data always needs to be tunneled to its destination so encapsulation must be used.
3. Each layer of the OSI model uses compression to put the PDU from the upper layer into its data field. It adds header and trailer information that is available to its counterpart on the system that will receive it.
4. Each layer of the OSI model uses encapsulation to put the PDU from the upper layer into its data field. It adds header and trailer information that is available to its counterpart on the system that will receive it.
6. Routers can be configured using several sources. Select which of the following sources can be used.
1. Console Port
2. Virtual Terminals
3. TFTP Server
4. Floppy disk
5. Removable media
7. Which memory component on a Cisco router contains the dynamic system configuration?
1. ROM
2. NVRAM
3. Flash
4. RAM/DRAM
8. Which combination of keys will allow you to view the previous commands that you typed at the router?
1. ESC-P
2. Ctrl-P
3. Shift-P
4. Alt-P
9. Which commands will display the active configuration parameters?
1. show running-config
2. write term
3. show version
4. display term
10. You are configuring a router, which prompt tells you that you are in the privileged EXEC mode?
1. @
2. >
3. !
4. :
5. #
11. What does the command “IP name-server 255.255.255.255″ accomplish?
1. It disables domain name lookup.
2. It sets the domain name lookup to be a local broadcast.
3. This is an illegal command.
4. The command is now defunct and has been replaced by “IP server-name ip any”
12. The following selections show the command prompt and the configuration of the IP network mask. Which two are correct?
1. Router(config-if)#netmask-format { bitcount | decimal | hexadecimal }
2. Router#term IP netmask-format { bitcount | decimal | hexadecimal }
3. Router(config-if)#IP netmask-format { bitcount | decimal | hexadecimal }
4. Router#ip netmask-format { bitcount | decimal | hexadecimal }
13. Which layer is responsible for flow control with sliding windows and reliability with sequence numbers and acknowledgments?
1. Transport
2. Application
3. Internet
4. Network Interface
14. Which processes does TCP, but not UDP, use?
1. Windowing
2. Acknowledgements
3. Source Port
4. Destination Port
15. Select which protocols use distance vector routing?
1. OSPF
2. RIP
3. IGRP
4. PPP



Networking and Unix interview questions

• What is UTP?

UTP — Unshielded twisted pair 10BASE-T is the preferred Ethernet medium of the 90s. It is based on a star topology and provides a number of advantages over coaxial media:
It uses inexpensive, readily available copper phone wire. UTP wire is much easier to install and debug than coax. UTP uses RG-45 connectors, which are cheap and reliable.

• What is a router? What is a gateway?

Routers are machines that direct a packet through the maze of networks that stand between its source and destination. Normally a router is used for internal networks while a gateway acts a door for the packet to reach the ‘outside’ of the internal network

• What is Semaphore? What is deadlock?

Semaphore is a synchronization tool to solve critical-section problem, can be used to control access to the critical section for a process or thread. The main disadvantage (same of mutual-exclusion) is require busy waiting. It will create problems in a multiprogramming system, where a single CPU is shared among many processes.
Busy waiting wastes CPU cycles.
Deadlock is a situation when two or more processes are waiting indefinitely for an event that can be caused by only one of the waiting processes. The implementation of a semaphore with a waiting queue may result in this situation.

• What is Virtual Memory?

Virtual memory is a technique that allows the execution of processes that may not be completely in memory. A separation of user logical memory from physical memory allows an extremely large virtual memory to be provided for programmers when only a smaller physical memory is available. It is commonly implemented by demand paging. A demand paging system is similar to a paging system with swapping. Processes reside on secondary memory (which is usually a disk). When we want to execute a process, we swap it into memory.

• Explain the layered aspect of a UNIX system. What are the layers? What does it mean to say they are layers?

A UNIX system has essentially three main layers:
. The hardware
. The operating system kernel
. The user-level programs
The kernel hides the system’s hardware underneath an abstract, high-level programming interface. It is responsible for implementing many of the facilities that users and user-level programs take for granted.
The kernel assembles all of the following UNIX concepts from lower-level hardware features:
. Processes (time-sharing, protected address space)
. Signals and semaphores
. Virtual Memory (swapping, paging, and mapping)
. The filesystem (files, directories, namespace)
. Pipes and network connections (inter-process communication)