Graphics Cards & Displays

Displays

Flat panel PC monitors can receive either an analog signal, or a digital signal from a video card. There are various technologies that the monitor might have:

• Liquid Crystal Display 
• Plasma Display Panel - that uses a gas plasma display
• ElectroLuminescent Display
• Light Emitting Diode

The Quality of a display is measured in two areas,

• Dot Pitch: this is the shortest distance between two dots of the same colour on the monitor, measured in millimeters (0.28mm is average).
• Refresh rate: this is the amount of times per second that the screen is redrawn and is measured in Hz. The standard is 60Hz for VGA (Video Graphics Array).

The resolution of a screen is the measure of how many dots on the screen are addressable by software. These addressable dots are known as pixels. Most monitors have a resolution of 1024 x 768 or higher. The video card also has to be able to support the resolution as well as the monitor.

Graphics Cards

Graphics cards are known by various names, some more common than others:

• Video cards
• Video boards
• Video display boards
• Graphics boards
• Graphics adapter cards
• Graphics accelerators

The graphics card (the term I prefer) creates an image from data being passed to it and holds it. Nowadays it is in the form of a 'plug in card', but older technologies used specialised circuitry to carry out the same task, but far slower than the newer technologies today.

A typical display adapter will take digital data sent from an application, store that data in Video Random Access Memory (VRAM), use a digital to analog converter to convert the data to something that the monitor can display, then send the data to the monitor through a VGA cable.

VGA adapters do not fully support digital monitors however. This is why a new standard has been introduced being the Digital Video Interface (DVI). DVI keeps the data in digital form from PC to monitor which has the advantage of eliminating any degradation of the signal quality during the data conversion. A DVI monitor and DVI compliant monitor is required for this.

A graphics card receives data and instructions from the processor, processes the data and sends it on to the monitor. A graphics card relies on the bus it uses (which influences its speed and performance), and the amount of video RAM it either has or can support and the chip set on the card. A graphics card card be improved by having its own processor, this is known as a graphics accelerator.

A graphics accelerator has a processor that is specially designed to handle video and graphics. They are increasingly becoming far faster than the PC's CPU as they are required to calculate thousands of pixels maybe hundreds of time a second second. Imagine playing Call of Duty for example on a 32 inch screen. Roughly 1360 x 760 pixels, that's over a million pixels that have to be assigned a different colour multiple times a second. That Is why a GPU has to be so powerful. They are being used more and more frequently and have been used as a way to crack passwords because they are so fast at carrying out multiple calculations.

Main manufacturers of graphics cards include AMD, Nvidea and ARM.

Hard Drives

Hard Drives

A hard drive is a series of magnetic disks that 'in essence' store a series of 1's and 0's that translate into different types of data.

A hard disk will be constantly spinning whilst the device is turned on, at a rate of around 7200 revolutions per minute. Obviously this is going to create a lot of heat so the cooling of the hard disc is crucial.

Properties of a hard drive include:

• its Capacity
• its expected lifespan
• the drives access time
• the drives seek time
• the drives Latency

The capacity of a disc is calculated by the following:

(No. bytes per sector) x (no. sectors per track) x (no. tracks per cylinder) x (no. cylinders per disc)

A hard drives lifespan is referred to as its MTBF, or 'mean time before fail'.

The drives access time is derived from - Seek time + latency.

The drives seek time is the time it takes to locate the required cylinder on the disk.

The drives latency is the time it takes for the arm to move to the required cylinder on the disk.

An alternate hard drive to the disk drive is becoming more and more popular, the Solid State Disk (SSD).

Solid State Disk

A solid state disk has no moving parts within which has certain advantages on its predecessor. 

• No moving parts mean less likely that the disc is damaged when being moved.
• The seek time is reduced.
• Less latency
• Quieter with no noise at all.

The SSD is more expensive though.

Servers

A server needs a good architecture so that when a failure occurs, all the information on that server is not lost.

RAID (redundant array of inexpensive disks) is a data storage facility that uses multiple hard drives logically to eliminate the risk of data loss upon failure. A raid system has to have at least one RAID controller.

There are multiple RAID architectures that are named from 0 to 5.

RAID 0:

RAID 1:

From this architecture you can see that drive 1 (split into 6 blocks) is basically mirrored into drive 2, meaning that if one disk fails, the back up is still there with all the data. This was the case in the twin towers, one drive in each tower. But obviously as both towers went down, all the data was lost. Now companies put each disk in different geographical locations.

RAID 0 & 1

This architecture takes RAID 1 & 0 and utilises both.

There are RAIDS 2,3,4 and 5 but they aren't generally used.

Storing on a CD

• Can hold up to 800 MB

Storing on a DVD

• Can hold up to 17 GB

Storing on Blu-Ray

• Can be dual layer, 25 GB per layer

Memory

Memory

Each different device will have different hardware, software and memory capabilities and restrictions. When designing a program for a certain device, for example a smart phone, research is crucial into the memory storage of the device, and how its interface relates to a specific browser.

Volatile Memory: Memory that you will lose once the device is powered down.

Non-volatile Memory: Memory that retains data once the power is shut off. Read only memories are the largest of these types.

More and more, browsers are starting to use non-volatile memory spaces to prevent annoying situations, for example, having to re-input user data upon a page refresh.

Random Access Memory (RAM)

Dynamic:

Data will leak even if power is on.
Based on capacitors.
Data must be refreshed about 1000 times a second.

Static (USB stick):

Will retain power as long as there is power.
Based on transistors.
Faster than DRAM but costs more.

Cache:

Fastest form of SRAM and also most expensive. Mainly utilised for holding most recent data.

Characteristics of RAM:

Capacity - The number of bytes that can be stored.
Speed - How quickly the data can be sent to the computer
Bandwidth - The rate at which the data can be sent to the computer
Technology - Typically DDR/DDR2/DDR3 soon to be entering the DDR4, as
the silicone is becoming smaller the voltage is also decreasing along the Buses.

When talking specifications, 50GB - the 'B' refers to eight bytes where as a specification of 100Mbps the 'b' refers to a byte.

All American standards are stated under IEEE. European standards are provided by ISO standards.