Chapter 2 D12 IT

Chapter 2
COMPUTER HARDWARE PROCESSING AND MEMORY
The CPU (Central Processing Unit)

A Central Processing Unit (CPU), or sometimes simply processor, is the component in a digital computer that interprets instructions and processes data contained in computer programs. CPUs provide the fundamental digital computer trait of programmability, and are one of the necessary components found in computers of any era, along with primary storage and input/output facilities. A CPU that is manufactured using integrated circuits is known as a microprocessor. Since the mid-1970s, single-chip microprocessors have almost totally replaced all other types of CPUs, and today the term "CPU" is usually applied to some type of microprocessor.
Inside the CPU
Components of CPU
ALU
(Arithmetic Logic Unit)

CU
(Control Unit) CPU Memory / Registers
Arithmetic Logic Unit

The ALU is the part of the CPU which carries out all of the
mathematical operations; it does the arithmetic which needs to be done, and it also performs all the logical operations (which we can loosely describe as "comparisons", such as "is A larger than B?"). The ALU is kind of like a slave which does what the control unit dictates.
Control Unit
The control unit is the nucleus of the CPU. It is the part of the CPU
which coordinates all of the activities going on within the computer, and manages the flow of data as it travels from place to place inside the machine. The control unit also houses the instruction set, the list of basic instructions which the CPU can execute. The instruction set is built into the circuitry of the control unit. There are three main functions of the control unit: It reads & interprets program instructions. It oversees and directs the internal operations of the computer's components. It controls and manages the flow of programs and data as they travel backwards and forwards between RAM and the CPU.
CPU Memory / Registers

The CPU needs somewhere to store data/instructions while it works on it. It has to "ship" the data into its own storage area, work on it, and then "ship" the results back out to RAM. This special form of memory is known as a register. The registers are special memory cells which are actually embedded into the CPU (i.e. the processor chip) and receive instructions/data from RAM which are to be executed/manipulated. They are temporary workspaces which the CPU must have in order to function, because otherwise it has nowhere to hold the items it is currently playing with. They can store no more than a few bytes each, but because they are actually part of the CPU they are very fast forms of memory (much faster than RAM).
Registers
Name of Register Functions
Memory Address Register (MAR) Holds the address of active memory location
Memory Buffer Register (MBR)

Program Control (PC)
Holds the data on its way form and to memory

Holds the address of next instruction to be executed
Accumulator (ACC)
Instruction Register (IR)
Accumulates results and data to be operated upon

Holds the instruction while it s being executed
Input/Output Register
Communicates with I/O devices
The Primary memory / Storage

Primary storage is directly connected to the CPU of the computer. It
must be present for the CPU to function correctly, just as in a biological analogy the lungs must be present (for oxygen storage) for the heart to function (to pump and oxygenate the blood) . As shown in the diagram, primary storage typically consists of three kinds of storage:
Various form of storage (on basis of distance from CPU)

Processor registers are internal to the central processing unit. Registers contain
information that the arithmetic and logic unit needs to carry out the current instruction. They are technically the fastest of all forms of computer storage, being switching transistors integrated on the CPU's silicon chip, and functioning as electronic "flip-flops". Cache memory is a special type of internal memory used by many central processing units to increase their performance or "throughput". Some of the information in the main memory is duplicated in the cache memory, which is slightly slower but of much greater capacity than the processor registers, and faster but much smaller than main memory. Multi-level cache memory is also commonly used - "primary cache" being smallest, fastest and closest to the processing device; "secondary cache" being larger and slower, but still faster and much smaller than main memory. Main memory contains the programs that are currently being run and the data the programs are operating on. The arithmetic and logic unit can very quickly transfer information between a processor register and locations in main storage, also known as a "memory addresses". In modern computers, electronic solid-state random access memory (RAM) is used for main storage, and is directly connected to the CPU via a "memory bus" (shown in the diagram) and a "data bus".
Cache memory
RAM (Random Access Memory)

Random-access memory (RAM) is a type of data store that allows the
stored data to be accessed at random, not just in sequence. RAM is the opposite of sequential access memory. Generally, RAM in a computer is considered main memory or primary storage: the working area used for loading, displaying and manipulating applications and data. This type of RAM is usually in the form of integrated circuits (ICs). These are commonly called memory sticks or RAM sticks because they are manufactured as small circuit boards with plastic packaging and are about the size of a few sticks of gum. Most personal computers have slots for adding and replacing memory sticks.
ROM (Read Only Memory)

Read-only memory (ROM) is a class of storage media used in computers and other electronic devices. Because it cannot (easily) be written to, its main uses lie in the distribution of firmware (software that is very closely related to hardware, and not likely to need frequent upgrading).Modern semiconductor ROMs typically take the shape of IC packages, i.e. "computer chips", not immediately distinguishable from other chips like RAMs but for the text printed on the chips. "ROM" in its strictest sense can only be read from, but all ROMs allow data to be written into them at least once, either during initial manufacturing or during a step called "programming"
Types of ROMs
PROMs (Programmable Read-Only Memory)
EPROMs (Erasable Programmable Read-Only
Memory) EAROMs (Electrically Alterable Read-Only Memory) EEPROM (Electrically Erasable Programmable Read-Only Memory)
PROMs
PROMs (Programmable Read-Only Memory) can be written to
(programmed) via a special device, a PROM programmer. The writing often takes the form of permanently destroying or creating internal links (fuses or antifuses) with the result that a PROM can only be programmed once.
EPROMs
EPROMs (Erasable Programmable Read-Only Memory) can be erased
by exposure to ultraviolet light then rewritten via an EPROM programmer. Repeated exposure to ultraviolet light will eventually destroy the EPROM but it generally takes many (greater than 1000) exposures before the EPROM becomes unusable. EPROMs can be easily identified by the circular 'window' in the top which allows the UV light to enter. Once programmed, this window is typically covered by a label to prevent accidental erasure.
EAROMs
EAROMs (Electrically Alterable Read-Only Memory) can be modified a
bit at a time, but writing is intended to be an infrequent operation; most of the time the memory is used as a ROM. EAROM may be used to store critical system setup information in a non-volatile way. For many applications, EAROM has been supplanted by CMOS RAM backed-up by a lithium battery.
EEPROM
EEPROM such as Flash memory (Electrically Erasable Programmable
Read-Only Memory) allow the entire ROM (or selected banks of the ROM) to be electrically erased (flashed back to zero) then written to without taking them out of the computer (camera, MP3 player, etc.). Flashing is much slower (milliseconds) than writing to RAM (nanoseconds) (or reading from any ROM).
THE PC MOTHER BOARD

A motherboard is a printed circuit board used in a personal computer. It is also known as the main-board and occasionally abbreviated to mobo or MB. The term main-board is also used for the main circuit board in this and other electronic devices. A typical motherboard provides attachment points for one or more of the following: CPU, graphics card, sound card, hard disk controller, memory (RAM), and external peripheral devices. The connectors for external peripherals are nearly always colour coded according to the PC 99 specification. All of the basic circuitry and components required for a computer to function sit either directly on the motherboard or in an expansion slot of the motherboard or are connected with a cable. The most important component on a motherboard is the chipset. It often consists of two components or chips known as the Northbridge and Southbridge, though they may also be integrated into a single component. These chips determine, to an extent, the features and capabilities of the motherboard.
THE PC MOTHER BOARD

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Chapter 2

COMPUTER HARDWARE PROCESSING AND MEMORY

The CPU (Central Processing Unit)

Inside the CPU

(Arithmetic Logic Unit)

(Control Unit) CPU Memory / Registers

Arithmetic Logic Unit

CPU Memory / Registers

Memory Buffer Register (MBR)

Holds the data on its way form and to memory

Accumulates results and data to be operated upon

Communicates with I/O devices

The Primary memory / Storage

Various form of storage (on basis of distance from CPU)

RAM (Random Access Memory)

ROM (Read Only Memory)

EPROMs (Erasable Programmable Read-Only

THE PC MOTHER BOARD

THE PC MOTHER BOARD

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