What is Memory?
- hardware that stores data temporarily or permanently.
- Capacity refers to the amount of data that can be stored.
- Information is stored as a single bit (1 or 0) - 8 bits is referred to as a byte and is the smallest measurement of data.
- Capacity has exponentially increased over time, which is known as Moore's law.
Common Memory terms:
- Formatting - The process of preparing a storage device for use. It creates an indexing system that allows written data to be accessed and organized in a consistent and efficient manner.
- Reading - The process of loading data from the storage medium onto the computer's main memory.
- Writing - is the transfer of data from the main memory to a storage medium.
- Seeking - The alignment of the read/write heads over an area where data needs to be written or read.
- Access method - Sequentually is when data is looked for in a sequential manner until data is found. The direct method is when the data location is addressed and data can be accessed immediately.
RAM ( Random Access Memory):
This is also called the main memory of the computer. It is a volatile memory. Memory is made up of virtual and physical memory. Physical memory is made up of electronic chips inserted into specific memory sockets on the motherboard. RAM is physical memory that enables data - that is in use - to be accessed quicker than it would from the hard drive. Virtual memory gives the idea of unlimited RAM when the RAM's use limit is reached, the computer searches for infrequently used instructions, and copies them into the hard drive in an area called a page file.
Memory is stored in bits. Semiconductor units consist of transistors and capacitors. The capacitor holds the bit, and the transistor enables an electronic circuit to read or modify the bit.
Cache
Cache is memory that is stored just outside the CPU, Caching stores data that allows the CPU to quickly receive frequently used instructions, therefore enabling the system to operate fluently.
ROM
ROM is used in computers and devices that need data that does not or is infrequently changed. Typically, ROM keeps instruction sets referred to as firmware. Data in ROM will not be lost when power is cut (non-volatile).
Five typical measurements of data:
- Byte(B) - - 1
- Kilobyte(KB) - 1000
- Megabyte (MB) - 1 000 000
- Gigabyte(GB) - 1 000 000 000
- Terabyte (TB) - 1 000 000 000 000
Secondary Memory:
Memory that keeps it's data even when power to the device is lost. A PC's hard drive is referred to as it's primary storage. Storage mediums like USB's are known as secondary memory.
Storage Devices:
1. Hardrive disks:
- Traditional PC has at least one hard disk drive holding the OS.
- These devices are magnetic and non-volatile.
- Devices consist of a platter(metal disc) and a read-write head that floats on a cushion of air.
- All data is addressed to the head can move directly to the location where the wanted data is located.
2. Floppy disk:
- magnetic storage devices
- Requires a ploppy reader with a head similar to those of a hard disk drive.
- The last popular size for floppy disk was the 3.5 in, which refers to the size of the plastic housing. The disk could only store 1.44 MB and was popular from the early 1990s to the mid-2000s.
3. Tape Drives:
- Magnetic storage device
- Useful for backing up systems.
- Tape drive stores data on tapes.
- the tape is removed and replaced when it's capacity has been reached.
- Tapes are favored because of their affordability, reliability, low power consumption and portability.
- Tapes can be damaged by fluids or heat but are more reliable than most storage devices.
- A drive may store up to 10 TB at a time. This information is ready to be read and enterprise-sized libraries of drives can store petabytes (thousands of terabytes) of data that can be accessed and loaded robotically.
4. Optical discs:
- Compact discs or digital versatile discs are optical storage mediums used to store audio and video material.
- CD-ROM are discs that are read-only - data is preloaded.
- CD-R and DVD-R are discs that can be written once, and then would only be read-only
- CD/DVD-RW can be written repeatedly.
- CD's typically hold 700MB of capacity, and DVD's 4GB and can have two layers.
- Today, DVDs have been superseded by Blu-Ray discs. Blu-Ray technology allows a disc to have a greater storage capacity of 25 GB per layer. The laser used to read the disc is blue rather than the red used with CDs and DVDs.
