3.1 Computer Architecture

(a) Describe CPU (Central Processing Unit):

CPU is the brain of the computer, made up of an Integrated circuit built inside a silicon chip called Microprocessor.

The CPU is made up of three main components — the Control Unit, the Immediate Access Store (IAS), and the Arithmetic Logic Unit (ALU).

The Control Unit controls the flow of data between different components using Address-bus, Data-bus and Control-bus; regulates and integrates the operation of the computer.

The Immediate Access Memory is where the CPU holds all the data and programs that it is currently using.

The Arithmetic Logic Unit (ALU) is where the CPU performs all arithmetic and logic operations.

CPU is responsible for the execution of all instructions and processing data.

(b) Explain the purpose of CPU:

The purpose of CPU is to process data and execute all instructions.

• Perform basic arithmetic calculation and logic operations.
• Control all the components of computer and perform input/output (I/O) operations specified by the instructions in the program.
• Fetch each instruction from main memory RAM, decode and execute it sequentially.

(c) Word size of CPU:

The Word size refers to the number of bits a CPU can process at a time (like 8-bit, 16-bit, 32-bit, 64-bit).

The bigger the word size, the better the CPU's performance will be.

(d) System Clock and Clock cycle / speed:

System Clock is an internal clock within the CPU that regulates the timing and speed of execution of instructions, and synchronizes all computer operations.

Clock cycle or speed refers to the number of cycles or instructions a CPU can execute per second. It is measured in MHz (Mega Hertz — 1 million cycles per second) or GHz (Giga Hertz — 1 billion cycles per second).

(e) Computer Register:

A Register is a data-holding place built inside the CPU, extremely faster than main memory RAM.

Registers are of two types — general purpose and special purpose register.

• General purpose register — discrete memory locations within CPU, used to hold data and instruction temporarily which are currently in execution.
• Special purpose register — has a specific data-handling task to carry out (e.g. PC, MAR, MDR, CIR).

(f) Difference between Cache and RAM memory:

• Cache memory is built inside the CPU, extremely faster than main memory RAM.
• Cache memory uses SRAM technology, while RAM uses DRAM technology in general.
• Cache memory stores frequently used instructions and data that need to be accessed faster.
• When a CPU wishes to read memory, it will first check the cache and then move to main memory RAM if the required data isn't there.
• The larger the cache memory size, the better the CPU performance.

(g) Core of the processor:

Core refers to the number of Processing units (CPU) built inside a single Microprocessor.

Each Processing unit has its own Control Unit, ALU, Cache and Registers which can perform all its tasks independently.

• Dual-core processor — contains two CPUs, giving twice the performance of the normal computer. It can process two instructions simultaneously.
• Quad-core processor — contains four CPUs, which divides data for processing by four units.

Multiple cores allow PCs to run multiple processes at the same time with greater ease, increasing its performance.

(a) System Bus:

System Bus is a pathway that carries data using parallel transmission between major components of a computer system.

Bus width refers to the number of bits it carries in parallel simultaneously at a time. The common data bus widths include 8-bit, 16-bit, 32-bit and 64-bit.

The wider the bus width, faster would be the data flow on the bus and thus better system performance.

(b) Three Buses used by the CPU:

★ Address Bus:

• Carries memory location address throughout the computer system, in order to either read data from, or write data to, that memory location.
• Between CPU and main memory (RAM), it is uni-directional (from CPU to main memory only).
• The width of the address bus determines how many unique memory locations can be addressed at a time simultaneously.

Example:

• A bus of width 8-bit can convey 2⁸ = 256 different addresses = 256 bytes of memory.
• A bus of width 16-bit can address 2¹⁶ = 65536 ÷ 1024 = 64 KB of memory.
• A bus of width 32-bit can address 2³² = 4 294 967 296 ÷ (1024 × 1024 × 1024) = 4 GB of memory.

The wider the bus, the more memory a computer can use.

★ Data Bus:

• Data Bus is bi-directional, allowing data to be sent in both directions between CPU and computer memory or input/output devices.
• The width of the data bus determines how many bits of data (i.e. word length) that can be transported at a time.
• The wider the bus, the larger the word-length a computer can transport.

Example:

• A bus of width 8-bit can transfer 1 byte of data per read/write cycle.
• A bus of width 16-bit can transfer 2 bytes of data per read/write cycle.
• A bus of width 32-bit can transfer 4 bytes of data per read/write cycle.

★ Control Bus:

• Control Bus is bi-directional, that carries control signals from Control Unit of CPU to other components and devices connected to the computer. The devices also communicate with CPU using control bus.
• Examples of control signals: memory read/write signals, device interrupt signal and status signals.
• The control bus also carries the clock's pulses of system clock needed to synchronize all the operations of computer.
• It is usually 8-bit wide. Since it only carries control signals, width of the control bus does not affect the performance of CPU.

(a) Von Neumann Architecture:

The Von Neumann architecture is a design model for a stored-program digital computer.

It stores both program and data in the same read-write memory, accessible by its location.

The CPU fetches instruction from main memory RAM, decodes and executes it sequentially called Fetch-Execute cycle.

Its Central Processing Unit (CPU) consists of Memory Unit (Registers), Control Unit and Arithmetic Logic Unit for processing.

(b) Fetch-Execute cycle:

The Fetch-Execute Cycle is a standard cyclic method of processing data by the CPU.

• CPU fetches a single program instruction or data from main memory (RAM) and stores it in a suitable register.
• Determines what CPU has to do by decoding the instruction and carries out those actions sequentially.
• This cycle is repeated continuously by the CPU, from boot-up to when the computer is shut down.

(c) Advantages of Von Neumann Architecture:

• Stores both program and data in the same memory accessible by its location, so no need to have two separate memory.
• No need to have two separate processors to process program and data separately in parallel.

(a) Read operation — read content of memory location 1000 0001:

MAR holds the address, MDR holds the content at that address.

(b) Write operation — write 0111 1001 into memory location 1000 1110:

MAR holds the address, MDR holds the data to be written.

(c) Computer memory after read and write operations:

Note: Read operation does not change memory contents. Only the write operation changes the content of location 1000 1110 to 0111 1001.

(a) Embedded system — describe with example:

An embedded system is a microcontroller or microprocessor-based hardware system with embedded software designed to do only some specific tasks.

It is capable of performing its task either independently, or by being a part of a larger system.

Embedded software is called firmware, which is stored in ROM that tells the microcontroller how to respond to the data provided to it.

Examples:

• Electronic Calculator
• Digital Watch
• Domestic home appliances — TV, Electric Oven, Dishwasher, Home Theater (Sound system)
• ATM and Vending machines
• Central heating systems
• Engine management system in vehicles
• GPS System

(b) Difference between Microprocessor and Micro-controller:

(c) How an Embedded System works:

1. It takes the analogue/digital input, automatically from sensors or by user through suitable input devices, and sends it to the microcontroller.
2. ADC (Analogue to Digital Converter) is used to convert the sensor's analogue data to digital.
3. Embedded software tells the microcontroller how to respond to the data provided to it, managing output devices to produce the expected result.
4. DAC (Digital to Analogue Converter) is used to convert digital data into analogue signals for Actuators to do some mechanical work if needed.

(d) Four features of embedded systems:

1. Performs one or very few dedicated tasks.
2. Uses embedded software, doesn't need any operating system.
3. Cannot be changed or upgraded by the user.
4. Could perform its task either independently or by being a part of a larger device/system.
5. Built to do the same task repeatedly or continuously with little or no human intervention (e.g. a fully automatic washing machine).
6. Performs the task within a certain time frame (e.g. a car's brake system; if it exceeds the time limit, may cause accidents).
7. Small sized, consume less power and are not too expensive.

(a) Tasks controlled by the embedded system in a digital camera:

1. Operate the flash automatically.
2. Focus the image automatically.
3. Adjust the shutter speed automatically.
4. Adjust the aperture size automatically.

(b) Applications where a digital camera could be used:

1. Photography and Video shoots for personal use — take pictures or videos, check instantly and retake if necessary. Store in solid-state memory for later use.
2. Verify the identity of a passenger at the airport — take a picture of the passenger and compare it with the scanned image or image stored in the database.
3. Webcam for video conferencing over the internet.
4. CCTV / Security camera for surveillance purposes.
5. Produce 360° image of the surroundings for Virtual Reality.
6. Produce 3D image of an object.

(a) Inputs and outputs of the embedded system:

Inputs:

• Game console receives input about the position and movement of the object from sensors, and commands from player through input devices like steering wheel, push of a button, or twist of the control stick (joystick).
• Embedded Accelerometers measure acceleration and deceleration and respond to the twist of control stick to move a character or object forward/backward and side to side.
• Proximity sensors used in smart touch pads with electrodes (control stick) can detect the movement of hand/finger to select and interact with the character or objects on screen.

Outputs:

• Embedded accelerometers and proximity sensors together with microcontroller allow human to interact with the game, simulate real-time events to give an immersive gaming experience.

(b) Updating device software without sending back to manufacturer:

• Embedded systems can be connected to the internet and the latest version of the device software could be updated from the manufacturer's website automatically.
• Automatic updates could also be received by plugging the device into a computer and updating the software over its internet connection via cellular network, WiFi or Bluetooth.
• New games could be downloaded and stored in the device SSD memory from the website.
• The player can play new games by inserting the memory stick in the games console, loading it into its main memory (RAM) and executing it by its microcontroller.