Type of firewalls

A firewall is a network security device that monitors and filters incoming and outgoing network traffic in accordance with previously established security policies in an organization. 

There are 3 types of firewalls:
*Packet filtering
*Stateful Filters
*Application layer

Packet filtering
A packet filtering firewall is a network security technique that regulates data flow to and from a network. Packet-filtering firewalls make processing decisions based on network addresses, ports, or protocols. Packet filtering firewalls are among the oldest firewall architectures.

Packet-filtering firewalls are very fast because there is not much logic going behind the decisions they make. They do not do any internal inspection of the traffic. One important function of packet filtering firewalls is to control and monitor network data to ensure its authenticity and compliance.

Stateful Filters
Stateful firewalls are capable of monitoring and detecting states of all traffic on a network to track and defend based on traffic patterns and flows. Stateful firewalls use modern extensions to track active connections, like transmission control protocol (TCP) and user datagram protocol (UDP) streams. By recognizing incoming traffic and data packets' context, stateful firewalls can better identify the difference between legitimate and malicious traffic or packages.

Application layer
An application firewall is a type of firewall that scans, monitors, and controls network, Internet and local system access and operations to and from an application or service.
Type of firewalls

Computer memory

Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. The term "memory", meaning "primary storage" or "main memory", is often associated with addressable semiconductor memory, i.e. integrated circuits consisting of silicon-based transistors, used for example as primary storage but also other purposes in computers and other digital electronic devices.

Memory plays an important role in saving and retrieving data. The performance of the computer system depends upon the size of the memory.

Memory size refers to the size of the RAM (Random Access Memory) and the mass storage - usually magnetic hard disks.

There are two main types of semiconductor memory
*Volatile/Primary memory
*Non-volatile/Secondary memory

Secondary memory or non-volatile memory is external and permanent in nature. The secondary memory is concerned with magnetic memory. Examples of non-volatile memory are flash memory (used as secondary memory) and ROM, PROM, EPROM and EEPROM memory (used for storing firmware such as BIOS).

Primary Memory is internal memory of the computer. Examples of primary/volatile memory are primary storage, which is typically dynamic random-access memory (DRAM), and fast CPU cache memory. The primary memory provides main working space to the computer.

Memory can be classified to:
· Random access memories (RAM)
· Sequentially accessible memory (SAM)
· Direct access memory (DAM)
· Contents addressable memory (CAM)
Computer memory