Platforms all over

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Platforms all over

Post by K.FITZGERALD on Fri Mar 27, 2015 9:28 am

I have complied together a few topics i have struggled with and supplied some information that should be sufficient to get a few marks for each sections. might be useful if anyone can expand on these sections.

Key things to think about in the different areas of the platforms unit.
Generations of Computers
1st Generation - Vacuum tubes are used for circuity. The use of magnetic drums and punched cards. Paper tape used for input and printouts for outputs. Software included the use of machine language (Binary 0’s and 1’s). The first gen computers were room sized compared to modern day computers. Computation time for these computers are Milliseconds.
2nd Generation – Transistors were brought in to replace the vacuum tubes meaning that computers became small faster and more efficient and reliable (and even cheaper). A magnetic core was use for primary memory and magnetic tape and disks for secondary storage. The rise of assembly language as programs were written in in. Computation time has decreased to micro-seconds. This is when the software industry is born.
3rd Generation – Integrated circuits consisting of multiple transistors on silicon wafers which allow for the speed of the computer to be increased and thus be more efficient. Keyboards and monitors have become input and output norms. The operating system of these computers all the interactions of applications running at simultaneous times. Makes use of high-level language and assembly languages. Computation speed is in Nano-seconds
4th Generation – The computers of this generation are large and then of a very large scale. The interation of transistors continues to improve the overall performance of the computer. Semiconductor memory replaces the magnetic cores, disks get larger and new periperhals and storage media comes to life. Introduction of GUI (Graphical user interface). Computations time is now Pico-Seconds

Operating Systems
User interface – Allows for the execution of programs. Allows the user to be enter commands and be able to manipulate files on the computer. It also accepts the input from peripherals such as the keyboard and mouse.
Application Programming Interface (API) – Acts as this interface for application programs and utilities to access the internal services provided by the operating system.
Kernel – Provides internal services, managing memory to locate and allocate space for programs. The Kernel also schedules times for each separate application to be executed and ran. Communication is also provided between executing programs. Security is also provided to the system by the Kernel.
File management system - Allocates and manages secondary storage
I/O driver – Input/ Output driver. Each control one or more hardware devices of similar types.

Bits & Bytes
Bitmap Images – Resolution dependent. When the size of a bitmap file is decrease, pixels are lost. When the size is increased, the file is given additional pixels which the computer thinks should be there/ or needed. The computer estimate colour values. Blurry, distorted image. These images are displayed on screen at approx. 100ppi.

Vector Images – Resolution independent. The file can be increased or decreased and still al lines will looks crisp and sharp. Font is a type of vector image. Vector images are not just restricted to rectangular shapes (allow for circular and 3d images to be crisp and sharp.)

Sound – Converted by being transmitted in sound waves. This is an analogue signal being transmitted in the form of voltages or currents. Before the storage of sound can occur, sound must be converted into a digital form. This is carried out by a digital converted. The converter samples the analogue signal. Each time this sampling occurs, the amplitude and the voltage/current of the wave representing this in a binary value. The more frequent sampling, it will give a much more accurate representation of the wave. CD Quality sampling = 44100times/seconds.

ASCII - Most common coding system. The orginal version was made up of 7 bits but the new, extended version is made up of 8 bits (2^8 = 256). This allows for 256 characters to be coded. Characters that can be represent in ASCII are :
All standard keyboard characters,
English (Latin) Letter – Upper & Lower
0-9 decimal digits
Characters such as space, enter and del
Other symbols
Unicode – An extension of ASCII which is a 16 bit system used. (2^16) Allowing for 65536 characters to be used using Unicode. Unicode is capable of storing characters in every language (such as Arabic, Greek etc.) used today and even ancient languages.

Writing Data to Memory
Writing data to memory is usually referred to as storing data to memory from the processor.
1. Set the address (of the memory location) on the address bus.
2. Set the read/write wire of the control bus low (i.e. request a write operation).
3. Set the address valid control wire high.
4. This address valid signal, together with the value on the address bus will activate the chip select wire on the appropriate memory chip.
5. Place the value to be stored onto the data bus.
6. The value on the data bus is then written into the correct memory location.
7. The read/write wire is now set high, while the address valid and chip select wires can now all be set low.
Reading Data from Memory
Reading data from memory is also called "loading" data from memory into the processor.
1. Set the address (of the memory location) on the address bus.
2. Set the read/write wire of the control bus high (i.e. request a read operation).
3. Set the address valid control wire high.
4. The address valid signal, together with the value on the address bus will activate the chip select wire on the appropriate memory chip.
5. The contents of the memory location will now be placed on the data bus.
6. Read the value from the data bus - usually into a register in the microprocessor.
7. The read/write, address valid and chip select wires can now all be set low.
The read/write wire is usually labelled R / W

Caches – Direct-mapped: For every Main Memory address there is a single cache location which can hold the data. If word is in the cache, the block which contains that data is identified by the cache index which is found directly from the address.
Fully associative – allows for a memory block to be located anywhere in the cache. Accessing a word allows for a full search of the cache to be made in order to see if the requestion block of data is present in the cache.
Set Associative – a compromise. Has a number of location (≥ 2)where the block of data can be located. Each Main memory block map to a certain set and all blocks in that set must be searched in order to find that requested block and tag field extended to identify the set’s numbers.

Server operating System - The operating system of the serve is designed to provide platforms for multi-users, for critical network applications. The operating system also allows for security to be provided along with stability and collaboration. Dedicated software tool for the server system (Web Servers, email agents & terminal services). These operating systems do typically lack GUI. Multi-user & Multi-task, frequently micro-processor.

Computer Bus – Bus master, bus slave and daisy chain arbitration.
Need to control access to the bus in order for a device to reserve it for use. 1 solutions is the introduction of 1 or more bus masters to initiate and control all bus transactions. The CPU is always a bus maters which initiates and controls the bus transactions on a computer with memory. Single bus master is computationally expensive. The processor must be involved in every bus transactions. Multiple bus masters require bus arbitration. A device wishing to use the bus asserts a bus request line and is (later) granted access. Each device has a bus priority & arbitration scheme serves by priority. The daisy chain arbitration is a simple scheme in which devices signal requests to bus arbiter, which pass bus grant signal through all devices from highest to lowest priority. If a device wants the bus, it will become the master and passes on a low bus grant signal. A release line is asserted on transaction complete. The daisy chain arbitration does not assure fairness meaning that low priority signals could be blocked. Central bus arbitration chooses fairly but can become a bottleneck

Write through and write back strategies for cache and virtual memory
Writing = if block is not in the cache, the block must be read from the main memory.
Write through = Data is written in to the cache and also Main Memory. Write buffers are introduced and used to prevent stalling the processor when the Main memory updates. Read misses for write through are cheaper – never requiring a write to main memory, easier to implement.
Write back – Data is only written to the cache and only modified blocks will be written to the main memory only when it has been replaced in the cache. Data is written back at cache speed rather than main memory speed. Multiple written to a block only require 1 writes to main memory.

Resistive vs. capacitive touch screen technologies
Resistive – touchscreen panel comprises of several layers, especially 2 thin transparent electrically resistive layers which are separated by a thin space. The top layer of the touchscreen has a coating on underside surface. One layer has conductive connections along the sides where another layer has the connections along the top and bottom of the layer. A voltage is applied to one layer and then is sensed by the other. When fingertip of stylus is pressed down on the outer screen, the 2 layers touch in order to become connected at that given point. Resistive technology is lower in cost. Only sufficient pressure is need to picked up by the device. The resistive touchscreen technology suffers from poorer contrast because they have additional reflections from the extra layer of material that is placed on the top layer of the screen.
Capacitive – consists of an insulator such as glass and is also coated with a transparent conductor. When the screen is touched, this results in a distortion of the screen’s electrostatic field, measurable as a change in capacitance. The screen does not pick up touches when the user has gloves or any other material when pressing down on the scree/

Hosts, hubs & devices in terms of USB connection topology
USB defines 2 types of hardware – hubs and devices. Up to 127 devices can be connected together in a tiered star topology but this is limited to 7 address bits. Physical wire segments are point-to-point between a host, hub and/or device. The system may only have one host which is connected to a hub or a single device. USB hubs may connect to another hub or to a USB device which the hubs providing multiple connection points. USB port supplies 5v of power.
USB 1.0 –Slow to medium data transfer application (storage devices) – 12mb/s
USB 2.0 – High speed data transfer – 480 mb/s
USB 3.0 – Super speed USB – 4.8 Gb/s


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