Clasification of computer

Answer 1

Computer memory can be classified into temporary and permanent storage. Temporary storage is referred to as RAM and this kind of memory is lost once the computer is switched off. Permanent storage is referred to as ROM.

Answer 2

In the early 1940s, memory technology mostly permitted a capacity of a few bytes. The first electronic programmable digital computer, the ENIAC, using thousands of octal-base radio vacuum tubes, could perform simple calculations involving 20 numbers of ten decimal digits which were held in the vacuum tube accumulators.

Volatile memory

Volatile memory is computer memory that requires power to maintain the stored information. Most modern semiconductor volatile memory is either Static RAM (see SRAM) or dynamic RAM (see DRAM). SRAM retains its contents as long as the power is connected and is easy to interface to but uses six transistors per bit. Dynamic RAM is more complicated to interface to and control and needs regular refresh cycles to prevent its contents being lost. However, DRAM uses only one transistor and a capacitor per bit, allowing it to reach much higher densities and, with more bits on a memory chip, be much cheaper per bit. SRAM is not worthwhile for desktop system memory, where DRAM dominates, but is used for their cache memories. SRAM is commonplace in small embedded systems, which might only need tens of kilobytes or less. Forthcoming volatile memory technologies that hope to replace or compete with SRAM and DRAM include Z-RAM, TTRAM, A-RAM and ETA RAM.

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Non-volatile memory

Non-volatile memory is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory (see ROM), flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape), optical discs, and early computer storage methods such as paper tape and punched cards. Forthcoming non-volatile memory technologies include FeRAM, CBRAM, PRAM, SONOS, RRAM, Racetrack memory, NRAM and Millipede.

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Management of memory It has been suggested that this article or section be merged into Memory management. (Discuss) Proposed since February 2011.

Main article: Memory management

Proper management of memory is vital for a computer system to operate properly. Modern operating systems have complex systems to properly manage memory. Failure to do so can lead to bugs, slow performance, and at worst case, takeover by viruses and malicious software.

Nearly everything a computer programmer does requires him or her to consider how to manage memory. Even storing a number in memory requires the programmer to specify how the memory should store it.

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Memory management bugs

Improper management of memory is a common cause of bugs.

In arithmetic overflow, a calculation results in a number larger than the allocated memory permits. For example, an 8-bit integer allows the numbers −128 to +127. If its value is 127 and it is instructed to add one, the computer can not store the number 128 in that space. Such a case will result in undesired operation, such as changing the number's value to −127 instead of +128.

A memory leak occurs when a program requests memory from the operating system and never returns the memory when it's done with it. A program with this bug will gradually require more and more memory until the program fails as it runs out.

A segmentation fault results when a program tries to access memory that it has no permission to access. Generally a program doing so will be terminated by the operating system.

Buffer overflow means that a program writes data to the end of its allocated space and then continues to write data to memory that belongs to other programs. This may result in erratic program behavior, including memory access errors, incorrect results, a crash, or a breach of system security. They are thus the basis of many software vulnerabilities and can be maliciously exploited.

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Early computer systems

In early computer systems, programs typically specified the location to write memory and what data to put there. This location was a physical location on the actual memory hardware. The slow processing of such computers did not allow for the complex memory management systems used today. Also, as most such systems were single-task, sophisticated systems were not required as much.

This approach has its pitfalls. If the location specified is incorrect, this will cause the computer to write the data to some other part of the program. The results of an error like this are unpredictable. In some cases, the incorrect data might overwrite memory used by the operating system. Computer crackers can take advantage of this to create viruses and malware.

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Virtual memory

Main article: virtual memory

Virtual memory is a system where all physical memory is controlled by the operating system. When a program needs memory, it requests it from the operating system. The operating system then decides what physical location to place the memory in.

This offers several advantages. Computer programmers no longer need to worry about where the memory is physically stored or whether the user's computer will have enough memory. It also allows multiple types of memory to be used. For example, some memory can be stored in physical RAM chips while other memory is stored on a hard drive. This drastically increases the amount of memory available to programs. The operating system will place actively used memory in physical RAM, which is much faster than hard disks. When the amount of RAM is not sufficient to run all the current programs, it can result in a situation where the computer spends more time moving memory from RAM to disk and back than it does accomplishing tasks; this is known as thrashing.

Virtual memory systems usually include protected memory, but this is not always the case.

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Protected memory

Main article: memory protection

Protected memory is a system where each program is given an area of memory to use and is not permitted to go outside that range. Use of protected memory greatly enhances both the reliability and security of a computer system.

Without protected memory, it is possible that a bug in one program will alter the memory used by another program. This will cause that other program to run off of corrupted memory with unpredictable results. If the operating system's memory is corrupted, the entire computer system may crash and need to be rebooted. At times programs intentionally alter the memory used by other programs. This is done by viruses and malware to take over computers.

Protected memory assigns programs their own areas of memory. If the operating system detects that a program has tried to alter memory that does not belong to it, the program is terminated. This way, only the offending program crashes, and other programs are not affected by the error.

Protected memory systems almost always include virtual memory

Answer 3

The computer is an electronic device that performs mathematical and logical calculations. Analog computer, digital computer and hybrid computer are the classifications of a computer.

Answer 4

The computers are broadly classified into four categories. The four categories includes the microcomputers, the minicomputers, the mainframe computers and the supercomputers.

Answer 5

Classification of computers according to operation can be dome into three man parts. The three categories are analogue, digital and hybrid computers.