The Central Processing Unit

CONTENTS

·  Introduction

·  Assignment 1

·  The Central Processing Unit

·  Components of the CPU

·  Types of Memory in the Hierarchy

·  Assignment 2

·  Post

·  CMOS

·  BOIS Programs

·  Buses

·  North and South Bridges

·  References

INTRODUCTION

Its cardinal for managers and business professionals to acquire knowledge in computer technology they should have a basic understanding of the role of hardware and software in the organization’s information technology (IT) infrastructure so that they can make technology decisions that promote organizational performance and productivity.

Computer hardware provides the underlying physical foundation for the firm’s IT infrastructure. Other infrastructure components such as software, data, and networks require computer hardware for their storage or operation.

A contemporary computer system consists of a central processing unit, primary storage, secondary storage, input devices, output devices, and communications devices.

ASSIGNMENT 1

1. With aid of a diagram, explain the stages the CPU goes through as it executes a

Program.

THE CENTRAL PROCESSING UNIT.

Sometimes referred to simply as the central processor, but more commonly called processor, the CPU is the brains of the computer where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.

On large machines, the CPU requires one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor as illustrated below in figure 4-5:

COMPONENTS OF A CPU

The Central Processing Unit is broken down into various typical components which assist in carrying out within the program such the arithmetic logic unit (ALU), the control unit (CU), the Integrated Circuit, Register, Read Only Memory, Random Access Memory, internal Memory, and the internal data bus and below are its attributes:-

Arithmetic and Logic Unit (ALU) :The ALU performs all of the calculations and comparative logic functions for the CPU, including all add, subtract, divide, multiply, equal to, greater than, less than, and other arithmetic and logic operations.

Control Unit (CU): At the risk of being obvious, the control unit controls the functions of the CPU. It is kind of like the manager who coordinates the activities between the different parts of a factory. It tells the other parts of the CPU how to operate, what data to use, and where to put the results.

Registers Built into the CPU are a number of holding areas and buffers that are used to temporarily hold the data, addresses, and instructions being passed around between the CPU’s components.

Memory Management Unit (MMU) The MMU handles the addressing and cataloging of where data is stored in system memory. Whenever the CPU needs something from memory, it requests it from the MMU. The MMU manages memory segmentation and paging allocations and translates all logical addressing into physical addressing for more information on memory addressing. However, Primary storage consists of RAM, ROM, and cache First of all you need to understand how the memory of a computer is organized. Bits and Bytes. The computer can work with two states ON and OFF. ON state is represented by 1 and OFF state is represented by 0. This system of using 1’s and 0’s is called as the binary system. A ‘0’ or a ‘1’ is called a bit. A collection of 8 bits is known as a byte. The computer’s internal memory is organized as a collection of bytes. The size of Memory available is measured in Kilobytes (KB) or Megabytes (MB). One Kilobyte represents 1024 bytes and one Megabyte represents 1024 Kilobytes.

The computer uses three types memory-the RAM, the ROM and cache. RAM Random Access Memory (RAM) is the area that is used for holding the programs and their data while the computer is working with them. RAM means the memory can be read from and written to randomly. The RAM is also known as short term memory because once the power is switched off all data in the RAM is erased.

It consists also of the components like Bus Interface Unit (BIU) which supervises the transfer of data over the bus system between the other components of the computer and the CPU. It also serves as the interface point for the CPU and its external bus, as well as handling all data transfers out of the control unit.

Control bus Carries the signals used by the CPU and the other components of the computer to communicate with each other, including when data is ready to be read, when another device wishes to use the bus, and the type of operation to be performed (read, write, interrupt).

The Computer’s primary storage or main memory is volatile and expensive. So, one need some storage device to store data and other information before or after the execution of data by the Central Processing Unit. It should be cheap and should not lose the content when power is switched off. This storage is called as the secondary storage. All secondary storage devices act both as input and output devices. Magnetic storage media fulfills these requirements and most common storage devices are disks and tapes.

2. From the figure given below, give a brief explanation on every type of memory shown in the hierarchy. [10 marks]

In computer architecture, a register is a quickly accessible location available to a digital processor's central processing unit (CPU). Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only. Registers are typically addressed by mechanisms other than main memory, but may in some cases be memory mapped.

Almost all computers, whether load-store architecture or not, load data from a larger memory into registers where it is used for arithmetic operations and is manipulated or tested by machine instructions. Manipulated data is then often stored back to main memory, either by the same instruction or a subsequent one. Modern processors use either static or dynamic RAM as main memory, with the latter usually accessed via one or more cache levels.

Registers are normally at the top of the memory hierarchy, and provide the fastest way to access data. The term normally refers only to the group of registers that are directly encoded as part of an instruction, as defined by the instruction set. However, modern high-performance CPUs often have duplicates of these "architectural registers" in order to improve performance via register renaming, allowing parallel and speculative execution.

The main memory is RAM which has bidirectional data bus that allows the transfer of data either from memory to CPU during a read operation or from CPU to memory during a write operation. The capacity of the memory is 128 words of eight bits (one byte) per word. This requires a 7-bit address and an 8-bit bidirectional data bus. The read and write inputs specify the memory operation and the two chip select (CS) control inputs are for enabling the chip only when it is selected by the processor.

Cache RAM: The CPU must deliver its data at a very high speed. The regular RAM cannot keep up with that speed. Therefore, a special RAM type called cache is used as a buffer - temporary storage. To get top performance from the CPU, the number of outgoing transactions must be minimized. The more data transmissions, which can be contained inside the CPU, the better the performance.

Cache RAM becomes especially important in clock doubled CPU's, where internal clock frequency is much higher than external. Then the cache RAM enhances the "horsepower" of the CPU, by allowing faster receipt or delivery of data. Beginning with 486 processors, two layers of cache are employed. The fastest cache RAM is inside the CPU. It is called L1 cache. The next layer is the L2 cache, which are small SRAM chips on the system board. The hard disk always has some cache RAM onboard. It serves as a buffer, so the data

being physically read is best utilized.

Magnetic disks are typically made of aluminum. There are also experiments with disks made of glass. The disks are covered with an ultra thin magnetic coating. With improved coating technologies, an increasing number of micro magnets can be placed on the disk. Currently, there more than 2000 tracks per inch disk radius. There are only 135 on a floppy disk. The narrower the tracks are, the bigger the disk capacity gets. At the same time the magnetic signals get weaker and weaker. Therefore, the read/write heads must get closer to the disk. This requires even smoother platters, etc. Another improvement in modern disks is the employment of a technology called Multiple Zone Recording. This allows for about twice as many sectors (120) in the outermost track as in the innermost. Thus, outer tracks, which are much longer, can hold much more data than inner tracks. Previously, all tracks had the same number of sectors, which was not very efficient.

Magnetic tape is the oldest form of magnetic mass storage. Tape systems served as the primary

Mass-storage technique for older mainframes (obsolescing the aging punched card and punched paper tape environment of the day). Tape systems proved to be inexpensive and reliable—so much so that even the original IBM PC was outfitted with a drive port for cassette- tape storage. With the development of floppy and hard drives, tape systems became obsolete as a primary storage method, but retain a valuable role as backup systems. Although the size, shape, and standards used for tape packaging and recording has advanced, the tape itself is virtually unchanged in principle from the very first incarnation. A tape is a long, slender length of polyester substrate, which is much more flexible than the mylarsubstrate used in floppy disks. Polyester also sustains a bit of stretch to help the tape negotiate the high tensions and sharp turns encountered in today’s tape cartridge assemblies.

3. Give a brief account on the technology used in Flash memory implementation

[2 marks]

Flash memory is the primary competing technology for secondary storage in the form of solid-state drives (SSDs), which have higher data transfer rates, better reliability, and significantly lower latency and access times.

They consists of ordinary transistors which are electronic switches turned on or off by electricity and that's both their strength and their weakness. A normal transistor has three connections (wires that control it) called the source, drain, and gate. Think of a transistor as a pipe through which electricity can flow as though it's water. One end of the pipe (where the water flows in) is called the source—think of that as a tap or faucet. The other end of the pipe is called the drain—where the water drains out and flows away. In between the source and drain, blocking the pipe, there's a gate. When the gate is closed, the pipe is shut off, no electricity can flow and the transistor is off. In this state, the transistor stores a zero. When the gate is opened, electricity flows, the transistor is on, and it stores a one. But when the power is turned off, the transistor switches off too. When you switch the power back on, the transistor is still off, and since you can't know whether it was on or off before the power was removed, you can see why we say it "forgets" any information it stores.

ASSIGNMENT 2

1. Explain the start-up process of a computer clearly indicating the purpose of the POST, BIOS and CMOS. [10 marks].

POST

POST stands for Power On Self Test is the first instruction executed during start-up. It checks the PC components and that everything works. You can recognize it during the RAM test, which occurs as soon as you turn power on. The duration of the POST can vary considerably in different Personal Computers. On the IBM PC 300 computer, it is very slow. But you can disrupt it by pressing [Esc]. If POST detects errors in the system, it will write error messages on the screen. If the monitor is not ready, or if the error is in the video card, it will also sound a pattern of beeps (for example 3 short and one long) to identify the error to the user. If you want to know more of the beeps, you can find explanations on the Award, AMI and Phoenix web sites.POST also reads those user instructions, which are found in CMOS.

CMOS

CMOS (Complimentary Metal Oxide Semiconductor) is a small amount of memory in a special RAM chip. Its memory is maintained with electric power from a small battery. Certain system data are stored in this chip. They must be read to make the PC operable. There may be 100 to 200 bytes of data regarding date, time, floppy and hard disk drives, and much more. CMOS data can be divided in two groups:

(i) Data, which POST cannot find during the system test.

(ii)Data, which contain user options.

THE BIOS PROGRAMS

BIOS is abbreviation of Basic Input Output System and those are programs, which are linked to specific hardware systems. During start-up, the BIOS programs are read from a ROM chip. For example, there is a BIOS routine, which identifies how the PC reads input from the keyboard.