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TOPIC 3.1: STORAGE SYSTEM CHARACTERISTICS - Coggle Diagram
TOPIC 3.1: STORAGE SYSTEM CHARACTERISTICS
Data Storage System
Storage devices
...computer hardware that records and/or retrieves items to and from storage media; hard disk drives, CD drives, DVD drives, blue ray drives, flash memory card reader
Internal (located inside the system unit)
External (plugged into an external port on the system unit)
Remote (located on another computer such as a network/web server)
Advantages
Requiring no additional desk space.
Faster than external counterparts.
Easily transported from one location to another.
Storage medium
...physical material on which computer keeps data, instructions & information.
Secondary storage; tape, hard disks, solid state, memory cards, USB flash, magnetic stripe cards
Removable. USB & flash drives - permanently sealed together to form one piece of hardware.
Definition
Data storage has expanded from text and numeric file to include digital music files, photographic files, video files etc.
These new types of files require secondary storage
devices with much greater capacity.
Storage holds data, instructions, and information for future use.
Storage Devices (cont...)
Regardless of how storage device are connected to a computer, letters of the alphabet and/or names are typically assigned to each storage device so that the user can identify device easily when it needs to be used.
Drive letter assignment
...process of assigning alphabetical identifiers to disk drives, logical disks or partitions; Local disk (C), Storage (D), Removable Disk (F)/(G), etc.
A: - Floppy disk drives, 3.5" or 5.25", and possibly other types of disk drives, if present.
B: - Reserved for a second floppy drive, if present.
C: - First hard disk partition.
D: to Z: - Other disk partitions get labeled here. The letter D: or E: are often assigned to CD-ROM, DVD drives but not always.
When a new storage device is detected, the computer just assign and reassigns drive letters as needed.
Access Method
Computer receives an instruction that requires data located on a storage medium - retrieve the requested data (this procedure referred to as access).
Basic access methods
Random
Direct access
Retrieved directly from any location, any order
Virtually all storage devices used with computer today are random access devices.
Media that allows random access sometimes referred to as addressable media.
Sequential
Retrieved in the order in which it is physically stored on the medium.
Example: magnetic tape drive, videotapes.
Access Time
Measures:
The amount of time it takes a storage device to locate an item on a storage medium.
The time required to deliver an item from memory to the processor.
The access time of storage devices is slow, compared with the access time of memory (memory accesses items in billionth of a second - nanoseconds)
Storage devices, access items in thousandths of a second (milliseconds) or millionths of a second (microseconds)
Capacity
Capacity is the number of bytes a storage medium can hold.
Storage Technology
A computer's processor works with data that has been coded into bits that can be represented by 0s and 1s.
The data is not literally written as 1 or 0. The 0s and 1s must be transformed into something that can remain on the surface of a storage medium.
How this transformation happens depends on the storage technology.
Types of Storage Technology
Magnetic
Optical
Solid state
Criteria for the Best
Storage Technology
Versatility
Durability
Speed
Capacity
Types of Storage
Primary
Volatile
Temporary
It loses all of its contents when power to the system unit is shut off.
Used to process data and instructions.
Secondary
Nonvolatile
Permanent
Writing: process of saving information
Reading: process of accessing information
Read Only Memory (ROM)
...used for storing programs and data permanently. The data and programs required for some applications are permanently store in the ROM chip. Thus a user may read a program or data from ROM but may not write on ROM.
Programmable Read Only Memory (PROM)
...blank chip which have nothing recorded on them. Once instruction or data recorded into the chip by a special programming device. The PROM permanently stores the information like ROM.
Erasable Programmable Read Only Memory (EPROM)
...can be programmed as the PROM chip, but they can be erased and reprogrammed by a special programming device.
The content of an EPROM chip can be erased by exposing it to ultraviolet light.
Electrically Erasable Programmable Read Only Memory (EEPROM)
...similar to EPROM expect that is erased by applying electrical pulses to the chip.
...possible to reprogram an EEPROM chip via keyboard commands without removing the chip from the computer.
Random Access Memory (RAM)
...temporary storage that can be read from or write into by the user. RAM is used primarily to store user programs and data. The content of RAM is generally volatile, and is lost when power is removed. When the system is powered up Programs and data to be used must be read into RAM through an input device.
Types of RAM
SRAM
Stands for static random access memory
Speed is high
Doesn't generally used for cache
SRAM's control complexity is less, it is a costly instrument
DRAM
Stands for dynamic random access memory
Works slowly
Requires refreshing periodically and used for main memory
DRAM's control complexity is high, it's cost is low
SDRAM
Synchronous DRAM designed to synchronize itself with the timing of the CPU.
This tends to increase the number of instructions that the processor can perform in a given time.
SDRAM speed is measured in Megahertz, which makes it easy to compare the processor's bus speed to the speed of the memory.
SDRAM is widely used in computers but known as generations of DDR RAM.