Bit Combinations - Chapter 1: Computer Systems

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Chapter 1: Computer Systems
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bet | 3/10 | Sana | 22.07.2024 | Hajmi | 225,5 Kb. | | #268238 |
Bog'liq slides01Bit Combinations - 000
- 001
- 010
- 011
- 100
- 101
- 110
- 111
- 0000
- 0001
- 0010
- 0011
- 0100
- 0101
- 0110
- 0111
- 1000
- 1001
- 1010
- 1011
- 1100
- 1101
- 1110
- 1111
- Each additional bit doubles the number of possible combinations
Bit Combinations - Each combination can represent a particular item
- There are 2N combinations of N bits
- Therefore, N bits are needed to represent 2N unique items
- 1 bit ?
- 2 bits ?
- 3 bits ?
- 4 bits ?
- 5 bits ?
- How many
- items can be
- represented by
A Computer Specification - Consider the following specification for a personal computer:
- 600 MHz Pentium III Processor
- 256 MB RAM
- 16 GB Hard Disk
- 24x speed CD ROM Drive
- 17” Multimedia Video Display with 1280 x 1024 resolution
- 56 KB Modem
- What does it all mean?
Memory - Main memory is divided into many memory locations (or cells)
- 9278
- 9279
- 9280
- 9281
- 9282
- 9283
- 9284
- 9285
- 9286
- Each memory cell has a numeric address, which uniquely identifies it
Storing Information - 9278
- 9279
- 9280
- 9281
- 9282
- 9283
- 9284
- 9285
- 9286
- Large values are
- stored in consecutive
- memory locations
- Each memory cell stores a set number of bits (usually 8 bits, or one byte)
Storage Capacity - Every memory device has a storage capacity, indicating the number of bytes it can hold
- Capacities are expressed in various units:
- Unit Symbol Number of Bytes
- kilobyte
- megabyte
- gigabyte
- terabyte
Memory - Main memory is volatile - stored information is lost if the electric power is removed
- Secondary memory devices are nonvolatile
- Main memory and disks are direct access devices - information can be reached directly
- The terms direct access and random access are often used interchangeably
- A magnetic tape is a sequential access device since its data is arranged in a linear order - you must get by the intervening data in order to access other information
RAM vs. ROM - RAM - Random Access Memory (direct access)
- ROM - Read-Only Memory
- The terms RAM and main memory are basically interchangeable
- ROM could be a set of memory chips, or a separate device, such as a CD ROM
- Both RAM and ROM are random (direct) access devices!
- RAM should probably be called Read-Write Memory
The Central Processing Unit - A CPU is also called a microprocessor
- It continuously follows the fetch-decode-execute cycle:
- Retrieve an instruction from main memory
- Determine what the
- instruction is
- Carry out the
- instruction
The Central Processing Unit (CPU) - Performs calculations and decisions
- Coordinates processing steps
The Central Processing Unit - The speed of a CPU is controlled by the system clock
- The system clock generates an electronic pulse at regular intervals
- The pulses coordinate the activities of the CPU
- The speed is measured in megahertz (MHz)
Monitor - The size of a monitor (17") is measured diagonally, like a television screen
- Most monitors these days have multimedia capabilities: text, graphics, video, etc.
- A monitor has a certain maximum resolution , indicating the number of picture elements, called pixels, that it can display (such as 1280 by 1024)
- High resolution (more pixels) produces sharper pictures
Modem - Data transfer devices allow information to be sent and received between computers
- Many computers include a modem, which allows information to be moved across a telephone line
- A data transfer device has a maximum data transfer rate
- A modem, for instance, may have a data transfer rate of 56,000 bits per second (bps)
Networks - A network is two or more computers that are connected so that data and resources can be shared
- Most computers are connected to some kind of network
- Each computer has its own network address, which uniquely identifies it among the others
- A file server is a network computer dedicated to storing programs and data that are shared among network users
Network Connections - Each computer in a network could be directly connected to each other computer in the network
- These are called point-to-point connections
- This technique is not feasible for
- more than a few close machines
- Adding a computer requires
- a new communication line
- for each computer already
- in the network
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