BS Computer Notes Chapter 5 Computer Memory
BS Computer Notes Chapter 5 Computer Memory. Computer memory is the storage space on a computer, where data is to be processed and instructions for processing are stored. Memory is divided into a large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one.
BS Computer Notes Chapter 5 Computer Memory
What is Computer Memory?
The computer memory is a storage area inside the computer system. Memory is mainly divided into two types: Primary Memory and Secondary Memory.
Primary memory is computer memory that a processor or computer accesses first or directly. It allows a processor to access running execution applications and services that are temporarily stored in a specific memory location. Primary memory is also known as primary storage or main memory.
Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks. The hard disk has enormous storage capacity compared to primary memory. The hard disk is usually contained inside the case of a computer.
RAM (Random Access Memory)
Random access memory (RAM) is a type of data storage used in computers that are generally located on the motherboard. This type of memory is volatile and all information that was stored in RAM is lost when the computer is turned off. There are two main types of RAM: dynamic random access memory (DRAM), or Dynamic RAM, and static random access memory (SRAM).
The RAM in most personal computers (PC’s) is Dynamic RAM. These RAM’s are made of capacitors. All dynamic RAM chips have to need a permanent refresh every few milliseconds by rewriting the data to the module.
Static RAM (SRAM) is a lot faster and does not require refreshing. It made from a complex circuitry system called a flip-flop. SRAM retains information and is able to operate at higher speeds than DRAM. It’s common to see PC manufacturers use DRAM and also used in supercomputers.
ROM (Read Only Memory)
Read-only memory (ROM) is a type of storage medium that permanently stores data on personal computers (PCs) and other electronic devices. It contains the programming needed to start a PC, which is essential for boot-up; it performs major input/output tasks and holds programs or software instructions. Because ROM is read-only, it cannot be changed, it is permanent and non-volatile, meaning it also holds its memory even when power is removed. There are large ROM chips located on the motherboard and a few on expansion boards. The chips are essential for the basic input/output system (BIOS), boot up, reading and writing to peripheral devices, basic data management, and the software for basic processes for certain utilities.
Types of ROM
The ROM is classified into the following types
- PROM (Programmable read only memory)
- EPROM (Erasable programmable read only memory)
- EEPROM (Electrically programmable read only memory)
It is a type of ROM which can be programmed once and then can never be changed.
EPROM is an erasable PROM. The stored data in EPROM can be erased by exposing it to ultra violet (UV) light for about 20 minutes. When it is exposed to UV light, the entire data is erased.
EPROM is a chip that can be erased and reprogrammed on the board. It can be erased within a few milliseconds.
Cache memory is a smallest type of volatile computer memory that provides high-speed data access to a processor and stores frequently used computer programs, applications, and data. It is the fastest memory in a computer, and is typically integrated onto the motherboard and directly embedded in the processor or main random access memory (RAM). Cache memory provides faster data storage and access by storing instances of programs and data routinely accessed by the processor. When a processor requests data that already in the cache memory it does not need to go to the main memory or the hard disk to fetch the data. Cache memory can be primary or secondary cache memory, with primary cache memory directly integrated into (or closest to) the processor. In addition to hardware based cache, cache memory also can be a disk cache, where a reserved portion of disk stores and provides access to frequently accessed data/applications from the disk.
A processor register (CPU register) is one of a small set of data holding places that are part of the computer processor. A register may hold an instruction, a storage address, or any kind of data (such as a bit sequence or individual characters). Some instructions specify registers as part of the instruction. Types of registers are:
- Accumulator register
- Status Register
- Instruction register
- Program counter
- Buffer Register
Types of Secondary Memory
Magnetic tape is one of the oldest technologies for electronic data storage. The tape has largely been displaced as a primary and backup storage medium, but it remains well-suited for archiving because of its high capacity, low cost, and long durability. It is a linear recording system that is not good for random access. If the tape is part of a library, robotic selection and loading of the right cartridge into a tape drive adds more latency. In an archive, such latencies are not an issue. With tape archiving, there is no online copy for quick retrieval, as everything is vaulted for the long term.
The hard disk was created in 1953 by engineers at IBM who wanted to find a way to provide random access to high capacities of data at a low cost. The disk drives developed were the size of refrigerators, could store 3.75 megabytes of data and began shipping in 1956. Memorex, Seagate, and Western Digital were other early vendors of hard disk drive technology. Hard disk drive form-factor size has continued to decrease as the technology evolves. By the mid-1980s, 3.5-inch and 2.5-inch form factors were introduced, and it was at this time they first became a standard in personal computers (PCs). Hard disk drive density has increased since the technology was first developed. The first hard disk drives were able to store megabytes of data, while today they are in the terabyte (TB) range. Hitachi released the first 1 TB hard drives in 2007. In 2017, HGST announced the first 10 TB hard drives.
Figure 9: Typical Hard Disk
Figure 10: Parts of a Hard Disk
Most basic hard drives consist of a number of disk platters that are positioned around a spindle inside a sealed chamber. The chamber also includes read-and-write heads and motors. The motor is used to spin the platters, which hold the data, at up to 15,000 rotations per minute (a higher rpm number result in a good performance). As the platters spin, a second motor controls the position of the read and-write heads that record information to, and read information from, tracks on each platter.
CD (Compact Disk)
A compact disc is a portable storage medium that can be used to record, store and playback audio, video and other data in digital form. A standard compact disc measure 4.7 inches, or 120 millimetres (mm), across is 1.2 mm thick, weight between 15 grams and 20 grams, and has a capacity of 80 minutes of audio, or 650 megabytes (MB) to 700 MB of data.
DVD (Digital Versatile Disk)
DVD is an optical disc technology with a 4.7-gigabyte storage capacity on a single-sided. Onelayered disk, which is enough for a 133 minute movie. DVDs can be single- or double-sided, and can have two layers on each side. A double-sided two-layered DVD will hold up to 17 gigabytes of video, audio, or other information. This compares to 650 megabytes (0.65 gigabytes) of storage for a CDROM disk.
Short for Digital Versatile Disc or Digital Video Disc, a DVD or DVD-ROM is a disc capable of storing large amounts of data on one disc the size of a standard Compact Disc. CD/DVD drives were first sold in 1997. They are widely used for storing and viewing movies and other data. To play DVDs on a computer, you must have a DVD drive and a software DVD player.
Blue- ray Disk
Blue ray is an optical disk format design to store large amount of data. Blue ray is the successor to DVD. Advantages over CD and DVD is that it has storage capacity of 50 GB to 100 GB. It is also faster than CDs and DVDs.
Flash memory is a type of non-volatile memory that erases data in units called blocks. A block stored on a flash memory chip must be erased before data can be written, or programmed, to the microchip. Flash memory retains data for an extended period of time whether a flash-equipped device is powered on or off.
Dr. Fujio Masuoka is credited with the invention of flash memory when he worked for Toshiba in the 1980s.