Introduction: Memory and Storage Organization
Digital systems can easily store large quantities of digital information and data for short or long periods. A major part of a computer is the memory unit. In a digital computer, the internal main memory stores instructions that instruct the computer what to do under all possible circumstances so that the computer can do its job with a minimum amount of human intervention. Computer and telecommunication systems therefore are dependent on large amounts of digital storage.
Memory and Storage Organization
Memories are classified in a number of ways. Some memories utilize semiconductor devices and are called semiconductor memories and others utilize magnetic materials. Bulk storage devices are commonly classified as either magnetic, mechanical, optical or semi conductor in nature.
The flip-flop forms a basic memory cell in some semiconductor memories. A group of lip-flops constitutes a register. A memory unit is a collection of storage cells together with associated circuits needed to transfer information in and out of the device. Data is stored in a memory by a process called writing and is retrieved from the memory by a process called reading.
A memory unit stores data or binary information in groups of bits called words. A word in a memory is an entity of bits that move in and out of storage as a unit. Each word consists of a sequence of 0’s and I’s. A word may represent a number, an instruction, one or more alphanumeric characters or any other binary coded information. Each word is stored in a memory location called its address.
At last, we can say that memory is an electronic circuitry that allows data to be stored and retrieved. The secondary memory stores the data and keeps it even when the electricity to the PC is cut off whereas the primary memory looses its contents on switching off power supply.
Memory and Storage Organization
Memory Terminology
(a) Memory Word: A group of bits (cells) in a memory that represents information or data of some type is known as memory word. Examples: A register containing 8 flip flops, the “natural” unit organisation of memory. The size of the word is typically equal to the number of bits used to represent a number and the instruction length. For example: the CRAY-1 has 1-64 bit word length but uses a 24-bits integer representation. The VAX has stupendous variety of instruction lengths, expressed as multiples of bytes and a word size of 32 bit.
(b) Byte: A group of B-bits (s and ‘i is called a byte. Word hints can be second in bytes as well as in bus. For example, a word size of 8-bits in also a wound size of abate a wound size of 16 bits is two bytes and so on
(c) Memory Cell: A device or an electrical circuit used to store a single bit (0 or 1) is A soon as memory cell. Examples: A flip-flop, a single magnetic core, a charged capacities and a single spot on magnetic tape or disk.
(d) Address: A number that identifies the location of a word us a memory is knower as address or selection of a cell in a memory array for read or write operation.
Memory and Storage Organization
(e) Capacity: The capacity of a memory it is usually stored as the total number of bytes for bus) that can be stored.
(F) Write Operation: The operation whereby a new word is placed into a particular memory location is known as write operation or store operation
(g) Read Operation: The operation whereby the binary word stored in a specific memory location (address) is sensed and transferred to another location is known as read peration
(h) Cycle time: The time required for the memory to perform a read or wrise aperation and then return to its original state ready for the next command is known as cycle time.
(I) Access time: The time required to locate and read a word from memory is called the access time. For random access memory, this is the time it takes to perform a read or write operation, that is the time from the instant that an address is presented to the memory to the instant data has been stored or made available for use. For non random access memory, access time is the time it takes to position the read or write mechanism at the desired location.
Memory and Storage Organization
(J) Volatile memory: Memories that require the application of electrical power to ore information are called volatile memories. If the electrical power is removed, all the information stored in a memory will be lost. Many semiconductor memories are volatile.
(k) Memory Cycle time: The time required for the memory to perform a read or write operation and return to its original state ready for the next command is known as cycle time. This concept is primarily applied to random access memory and consists of the access time plus any additional time required before a second access can commence. This additional time may be required for transients to die out on signal lines or to regenerate data if they are mad destructively.
(L) Non-Volatile Memory: Memory units that retain the stored information even when power is turned off are said to be non-volatile
(m) Random Access-Memory (RAM): The RAM is a Random Access Memory that has both read and write capability, RAM’s stored information can be recalled or membered
(n) Read only Memory (ROM): A memory device in which the data is permanently stored is called read only memory (ROM). The ROM is programmed by the manufacture to there’s specifications.
(o) Sequential Access Memory (SAM): A memory device in which the access time is not content depending on the spheres location. A particular stored word is found by wakening through off actions the desired address is reached.
(P) Storage Capacity: it is the amount of data that can be stored in the storage unit.
(q) Read and Write Memory (RWM): Any memory that can be read from or written into similar case.
(R) Dynamic Memory Devices: Semiconductor memories in which the stored data will unui pemase power applied, unless the data is periodically.
(S) Static Memory devices: Semiconductor memories in which the stored data will potently stored as long as the power is applied, without the need for periodically rewriting the data into a memory.
(T) Dynamic Memory devices: Semiconductor memories in which the stored data mordantly stored even with power applied unless the data is periodically rewritten into memory.
(U) Addressable Unit In many systems, the addressable unit is the bond. However, so slow addressing at the byte level in any case, the relationship between the length A of an mattress and the number of N of addressable units is 2-N.
(V) Unit of Transfers For main memory, this is the number of bits read out or written see thermos at a time. The unit of transfer needs to equal a word or an addressable ant, Fw external memory, data is often transferred in much larger units than a word, and this imed to a Mocks.
(w) Transfer Rate: This is the rate at which the data can be transferred in or out of a semaryst Fe random-access memory, it is equal to 1 (Cycle Time). For non random ace investors, the following relationship holds. TN-TA-N
Memory and Storage Organization
                                  R
TN Average Time to read or write N bits
TA Average access time N Number of bits
Transfer rate in bits per second (bps)
Direct Access: As with sequential Access, Direct access involves a shared read wete mechanism However, individual blocks or records have a unique address based on Rewal catius. in accomplished by direct access to reach a general vicinity plus Mpour sorching, couning or waiting to reach the final location again.
Memory and Storage Organization
