CAPE Computer Science K Hinds 1

CAPE Computer Science K Hinds

Bits, Words & Bytes Bit The smallest unit of data in a computer is called Bit (Binary Digit). A bit has a single binary value, either 0 or 1. The value of a bit is usually stored as either above or below a designated level of electrical charge within a memory device. For example, +5V representing ON or 1 OR 0V representing OFF or 0. A bit is abbreviated with a small “b” Word This is set of bits that acts as a single unit of data processed by microprocessor. However, it can be any set value, common values included: 16, 18, 24, 32, 36, 40, 48, and 64. "Word size" refers to the number of bits processed by a computer's CPU in one go (these days, typically 32 bits or 64 bits). Data bus size, instruction size, address size are usually multiples of the word size.

CAPE Computer Science K Hinds Byte A byte is a unit of data that is eight binary digits long. A byte is the unit most computers use to represent a character such as a letter, number or typographic symbol (for example, “g”, “5”, or “?”). In some computer systems, four bytes constitute a word, a unit that a computer processor can be designed to handle efficiently as it reads and processes each instruction. A byte is abbreviated with a “B”. Computer storage is usually measured in byte multiples. For example, an 820 MB hard drive holds a nominal 820 million bytes – or megabytes – of data. Byte multiples are based on powers of 2 and commonly expressed as a “rounded off” decimal number. For example, one megabyte (“one million bytes”) is actually 1,048,576 (decimal) bytes. Secondary Storage Devices Magnetic Tape This is a sequential storage medium used for data collection, backup and archiving. Like videotape, computer tape is made of flexible plastic with one side coated with a ferromagnetic material. Tapes were originally open reels, but were superseded by cartridges and cassettes of many sizes and shapes. Tape has been more economical than disks for archival data, but that is changing as optical disk capacities have increased enormously. If tapes are stored for the duration, they must be periodically recopied or the tightly coiled magnetic surfaces may contaminate each other. Due to the large size of tape reels, these storage devices were not readily portable. Floppy Disk A floppy disk, also called a diskette or just disk, is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. Floppy disks are read and written by a floppy disk drive (FDD) and had a maximum of 1.44MB of memory. These were readily portable than magnetic tape. This is a direct access storage device. Optical Disk (CD/DVD) CD/DVD’s are metal and plastic composed optical disks that stores data on circular tracks on one side of a CD/DVD. A special beam of light (laser) is shone onto the reflective side of the CD and the computer can read the information stored on the disk. A CD can hold about 700MB of information whereas a DVD can store about 4GB of information. Though this medium was larger than floppy disks, the demands of today are making these devices obsolete and they are clumsy to walk around with now. This is a direct access storage device. Trivia Time: What does the acronym CD and DVD stand for? Universal Serial Bus (USB) Drive This is a solid state device that requires no moving parts to store data. The USB drive consists of many transistors that are packaged close together on microchips that are all connected onto a small circuit board. The USB utilises the flash/EEPROM type of memory. USB drives are plugged into USB ports on computers for reading or writing data to them. The physical size of a USB drive is much smaller than a CD/DVD and they can store much more data. USB drives can be as large as 512GB although rumours of 1TB USB drives are circulating online. This is a direct access storage device.

CAPE Computer Science K Hinds Flash Memory Cards These cards utilise the EEPROM memory medium and come in many differing sizes and shapes. This form of memory is usually found in portable devices like cameras and cell phones. This is a direct access storage device. Hard Drives These are the most economical form of mass storage for computers today. HDD’s come in different flavours based on several factors like size, reliability, speed and affordability. This is a random access storage device. Moving Head HDD Internally, a hard drive consists of a platter that spins on an axis while an access/read head scans over the platter to read and write data to the drive. Hard Drives can come in sizes beyond 5TB and this limit is increasing daily as advances are made in HDD technology. Fixed Head HDD/Head per Track HDD These HDD carried one read/write head per track on the platter. This meant that time was saved because the head did not need to move to the requested track to read/write data. Due to the number of read/write heads these drives were expensive to manufacture are they are no longer in production. Solid State HDD These types of hard drives are referred to as solid state devices as there is no read/write head. The drive consists of EEPROM microchips that are more reliable that a spinning platter. Due to the cost of these EEPROM chips, these drives tend to cost more than regular platter HDD’s. External HDD These are drives that connect to the outside of the computer via an interface port (USB, eSATA, Firewire or iSCSI). These drives are handy for moving data from PC to PC and come in many sizes, shapes and speeds.

Homework Draw and state the salient points related to the following Computers/Components: 1. Super Computer, Mainframe, Microcomputer, Laptop & PDA. 2. UPS, Surge Protector & Voltage Regulator