System Unit

- RAM
- CACHE
- ROM
- FLASH MEMORY
- GRAPHIC CARD
- SOUND CARD
- NETWORK INTERFACE CARD
- PLUG AND PLAY
- UNIVERSAL SERIAL BUS PORT ( USB )
- SERIAL PORT
- PARALLEL PORT
- FIREWIRE PORT
- ETHERNET PORT
- HIGH DEFINITION MULTIMEDIA INTERFACE PORT (HDMI)

RAM
~ Random-access memory (RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. The first RAM modules to come into the market were created in 1951 and were sold until the late 1960s and early 1970s. However, other memory devices (magnetic tapes, disks) can access the storage data in a predetermined order, because mechanical designs only allow this.The two main forms of modern RAM are static Ram (SRAM) and dynamic Ram.

CACHE
~ Cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere. If requested data is contained in the cache (cache hit), this request can be served by simply reading the cache, which is comparatively faster. A cache is made up of a pool of entries.  the data has to be recomputed or fetched from its original storage location, which is comparatively slower. Hence, the more requests can be served from the cache the faster the overall system performance is.

ROM
~ Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware. ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. Despite the simplicity of mask ROM, economies of scale and field-programmability often make reprogrammable technologies more flexible and inexpensive, so mask ROM is rarely used in new products as of 2007.
Most personal computers ontain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators ad peripheral devices uch as laser printers, whose fonts are often stored in ROMs.

FLASH MEMORY
~ Flash memory refers to a particular type of EEPROM, or Electronically Erasable Programmable Read Only Memory. It is a memory chip that maintains stored information without requiring a power source. It is often used in portable electronics, like MP3 players, and in removable storage devices.
Flash memory differs from regular EEPROM in that EEPROM erases its content one byte at a time. This makes it slow to update. Flash memory can erase its data in entire blocks, making it a preferable technology for applications that require frequent updating of large amounts of data as in the case of a memory stick.
Inside the flash chip, information is stored in cells. A floating gate protects the data written in each cell. Tunneling electrons pass through a low conductive material to change the electronic charge of the gate in "a flash," clearing the cell of its contents so that it can be rewritten. This is how flash memory gets its name.

SOUND CARD
~ A sound card (also known as an audio card) is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware inside the PC. Typical uses of sound cards include providing the audio component for multimedia applications such as music composition, editing video or audio, presentation, education and entertainment (games) and video projection. Many computers have sound capabilities built in, while others require additional expansion cards to provide for audio capability.

- NETWORK INTERFACE CARD
Short for Network Interface Card, a NIC is also commonly referred to as a network adapter and is an expansion card that enables a computer to connect to a network such as a home network or the Internet using an Ethernet cable with a RJ-45 connector. To the right is a graphic example of an SMC EZ Card 10/100 PCI network card, a network card commonly found in most desktop computers today that do not already have an integrated network on their motherboard.

- PLUG AND PLAY

Plug and play is a term used to describe the characteristic of a computer bus, or device specification, which facilitates the discovery of a hardware component in a system, without the need for physical device configuration, or user intervention in resolving resource conflicts. Plug and play refers to both the boot-time assignment of device resources, and to hotplug systems such as USB and Firewire.

- UNIVER SAL SERIAL BUST PORT (USB)

Universal Serial Bus (USB) is a specification to establish communication between devices and a host controller (usually a personal computer), which has effectively replaced a variety of earlier interfaces such as serial and parallel ports.USB can connect computer peripherals such as mice, keyboards, digital cameras, printers, personal media players, flash drives, Network Adapters, and external hard drives. For many of those devices, USB has become the standard connection method.USB was designed for personal computers, but it has become commonplace on other devices such as smartphones, PDAs and video game consoles, and as a power cord. As of 2008, there are about 2 billion USB devices sold per year, and approximately 6 billion total sold to date.

a serial port is a serial communication physical interface through which information transfers in or out one bit at a time (contrast parallel port). Throughout most of the history of personal computers, data transfer through serial ports connected the computer to devices such as terminals and various peripherals. While such interfaces as Ethernet, FireWire, and USB all send data as a serial stream, the term "serial port" usually identifies hardware more or less compliant to the RS-232 standard, intended to interface with a modem or with a similar communication device. Some computers, such as the IBM PC, used an integrated circuit called a UART, that converted characters to (and from) asynchronous serial form, and automatically looked after the timing and framing of data. Very low-cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the so-called bit-banging technique. Before large-scale integration.

- PARALLEL PORT

A parallel port is a type of interface found on computers (personal and otherwise) for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port. The IEEE 1284 standard defines the bi-directional version of the port, which allows the transmission and reception of data bits at the same time.
Before the advent of USB, the parallel interface was adapted to access a number of peripheral devices other than printers. Probably one of the earliest devices to use parallel were dongles used as a hardware key form of software copy protection. Zip drives and scanners were early implementations followed by external modems, sound cards, webcams, gamepads, joysticks and external hard disk drives and CD-ROM drives. Adapters were available to run SCSI devices via parallel. Other devices such as EPROM programmers and hardware controllers could be connected parallel.

- FIREWIRE PORT
Firewire ports have been a standard in Apple computers for some time, and made an insurgence into the PC market when USB 1.0 just wasn’t cutting it. They tend to be used by older video cameras to off-load video to your hard drive. USB 2.0 put a hurt on the firewire market since their speeds were very close, and USB was more abundant in many computers. Also, firewire had a problem with using 2 kinds of ports…one carried power and the other didn’t. What’s more, the one that carried power carried too much, and would often over-heat and at times might even cause small fires or burn-outs in the port. With the introduction of USB 3.0 there will be very little, if any, need for firewire in the future.

- ETHERNET PORT
Ethernet is a family of frame-based computer networking technologies for local area networks (LAN). It defines a number of wiring and signaling standards for the Physical Layer of the standard networking model as well as a common addressing format and a variety of Medium Access Control procedures at the lower part of the Data Link Layer. 

- HIGH DEFINITION MULTIMEDIA INTERFACE PORT (HDMI)
HDMI (High Definition Multimedia Interface) is the industry supported, uncompressed, all-digital audio/video interface. HDMI provides an interface between any audio/video source, such as set-top box, DVD player, A/V receiver and audio/video monitors, such as digital television (DTV,HDTV) or plasma Monitor.