1. CHAPTER 4:
THE SYSTEM UNIT

2. OBJECTIVES
This chapter will present the components of the system unit.
Explain all functions of the system unit. Identify all the major components found inside the system unit.
Understand all stages of the machine cycle, and the benefits of pipelining.
Describe how memory stores data, instructions, and information.
Identify how the microprocessor works. Understand the how the computer processes all operations that occur when any command is executed.
Understand how does the computer represent data?
Identify the various types of memory and how it is represented?
Understand the importance of the Bios, Bus, and Cache?
Understand the difference between ports and connectors.
Explain the hard drive, solid-state drive (SSD), and external HD.

3. COMPONENTS AND FUNCTIONS
The main function of the computer system unit is to hold all the interior components together and protect the sensitive electronic components from harm. The computer case is designed with the concept for upgrades.
Some examples of the frequently used components are the power button, an optical disk drive, an audio jack for headphones, and several USB ports.
The rear of the unit contains other connections such as the power source, monitor, keyboard, mouse, Internet connections, and other peripheral device connections.

4. COOLING
The phrase cooling in computing refers to the dissipation of large amounts of heat created by a computer system.
Heat is generated inside the computer tower by various hardware devices such as CPU, video card, or even the hard drive.
The main objective of cooling is to maintain an optimal operating temperature.

5. THE MACHINE CYCLE
(1) Fetching the instruction or data item from memory
(2) Decoding the instruction into commands the computer understands 0’s and 1’s known as binary
(3) Executing the commands, and, if necessary
(4) Storing, or writing the result to memory of the computer

7. PIPELINING
Pipeline is continuous flow of activities, which is overlapped. Pipeline consists of the movement of instruction to the processor or in the arithmetic steps taken by the processor to perform an instruction.
With pipelining, the computer allows the next instructions to be fetched while the processor is performing arithmetic operations such as adding, holding them in a buffer.

8. ARITHMETIC LOGIC UNIT (ALU)
The ALU performs the execution part of the machine cycle. Specifically, the ALU carries out three operations:
Arithmetic operations—performing calculations, which include addition, subtraction, multiplication, and division
Comparison operations—comparing data items to determine if the first item is greater than, equal to, or less than the other item
Logical operations—working with conditions and logical operators such as AND, OR, and NOT

9. BYTE
NAME
SYMBOL
EQUAL TO
Kilobyte KB
1024 B
Kilobit
1000 bit
Megabyte MB
1024 KB
Megabit
1000 KB
Gigabyte GB
1024 MB
Gigabit
1000 MB
Terabyte TB
1024 GB
Terabit
1000 GB
Petabyte PB
1024 TB
Petabit
1000 TB
Exabyte EB
1024 PB
Exabit
1000 PB
Zettabyte ZB
1024 EB
Zettabit
1000 EB
Yottabyte YB
1024 ZB
Yottabit
1000 ZB
Most computers are digital, meaning they understand only two discrete states: on and off. These states are represented using two digits, 0 (off) and 1 (on).
Each on or off value is called a bit (short for binary digit), the smallest unit of data a computer can handle. One byte contains eight binary bits
Although the byte was originally designed to measure character data, it is now the fundamental unit of measurement for all data storage.

10. THE CENTRAL PROCESSING UNIT
A personal computer’s CPU usually contains a single chip, referred to as a microprocessor.
As it pertains to the functionality of a computer, the CPU is the most important element of a computer system.
The CPUs also uses high-speed storage locations, called registers, to hold data and instructions temporarily.
A standard computer will contain a minimum of one processor, this is the chip inside the CPU that performs calculations

11. COMPUTER SYSTEM BUS
The system bus is collection of wires through which data is transmitted from one part of a computer to another.
This bus connects all the internal computer components to the CPU and main memory.
All buses consist of two parts—an address bus and a data bus
The data bus transfers actual data whereas the address bus transfers information about where the data should go

12. RANDOM ACCESS MEMORY
RAM is a hardware device that allows information to be stored and retrieved on a computer
RAM is usually associated with D-RAM, which is a type of memory module. Because information is accessed randomly the computer can access the data much faster.
However RAM is a volatile memory that requires power to keep the data accessible. If the computer is turned off, all data contained in RAM is lost.

13. D-RAM AND S-RAM
DRAM (Dynamic Random Access Memory) is a type of RAM that stores each bit of data on a separate capacitor.
This is an efficient way to store data in memory, because it requires less physical space to store data.
However, the capacitors in DRAM need to be refreshed constantly to keep their charge, so DRAM requires more power than SRAM (Static Random Access Memory).
SRAM is more commonly used in cache and video card memory because it is faster.

14. ROM
ROM, called EEPROM (electrically erasable programmable read-only memory), can be erased electrically and rewritten.
The flash memory you find in USB memory sticks and digital camera memory cards is actually a kind of ROM that retains information

15. BIOS
The BIOS (Basic Input/Output System) is a program preinstalled on Windows-based that it uses to start up.
The CPU accesses the BIOS even before the OS is loaded. The BIOS then checks all your hardware connections and ensures all devices are working correctly. If everything is checked OK, the BIOS loads the OS into the computer's memory and finishes the boot-up process.

16. CACHE
Cache is a high-speed access area that can be a reserved section of main memory or storage device.
Cache has two main components: memory and processor cache
Memory cache is a portion of the high-speed static RAM (S-RAM) and is effective because most programs access the same data or instructions over and over. Memory cache keeps as much information as possible in S-RAM
The processor caches are even smaller than disk caches because a processor cache contains tiny blocks of data, such as frequently used instructions, that can be accessed quickly by the CPU

17. CACHE CONTINUED
The processor caches are even smaller than disk caches because a processor cache contains tiny blocks of data, such as frequently used instructions, that can be accessed quickly by the CPU.

18. PORTS AND CONNECTORS
Ports allow computers to access external devices such as printers.
A port is point of attachment to the system unit. Ports have different types of connectors, which are used to join a cable to a device
Most computers have three types of ports: serial, parallel, and USB.

19. TYPES OF PORTS AND CONNECTORS
A serial port is a type of interface that connects a device to the system unit by transmitting data only one bit at a time. Serial ports usually connect devices that do not require fast data transmission rates, such as a mouse, keyboard, or modem.
A universal serial bus (USB) port can connect up to 127 different peripheral devices with a single connector type, greatly simplifying the process of attaching devices to a personal computer.

20. TYPES OF PORTS AND CONNECTORS
A parallel port is an interface that connects devices by transferring more than one bit at a time. Many printers connect to the system unit using a parallel port.
A VGA port short for Video Graphics Array. VGA is a popular display standard developed by IBM and introduced in VGA provides 640 x 480 resolution color display screens with a refresh rate of 60Hz and 16 colors displayed at a time. If the resolution is lowered to 320 x 200, 256 colors are shown.

21. TYPES OF PORTS AND CONNECTORS
A DVI port short for Digital Video Interface. DVI is a video connection standard created by the Digital Display Working Group (DDWG). Most DVI ports support both analog and digital displays. If the display is analog, the DVI connection converts the digital signal to an analog signal.
A FireWire port is considered a high-speed interface, and therefore can be used for connecting peripheral devices that require fast data transfer speeds. Examples include external hard drives, video cameras, and audio interfaces.

22. TYPES OF PORTS AND CONNECTORS
Thunderbolt port is a high-speed Input and Output interface that was developed by Intel and was introduced by Apple in Thunderbolt can achieve performance that was previously only possible from internal components. Additionally, the Thunderbolt interface offers 10 Gpbs of throughput in both directions. That is more than 12 times as fast as Fire-wire 800 and over 20 times faster than USB 2.0.

23. HARD DRIVE
A hard disk drive is a nonvolatile memory hardware device that permanently stores and retrieves information
A hard drive can be used to store just about any type of data, including pictures, music, videos, and text documents.
Solid State Drive or Solid State Disk, SSD for short is a drive that uses nonvolatile memory as a means of storing and accessing data, much like computer RAM
Hard drives are not only inside the computer, there are external ones.