Computer Memory
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The document discusses the history and types of computer memory. It begins by describing early memory technologies from the 1940s like delay line memory and magnetic core memory. Random access memory later emerged in the 1940s including the Williams tube and Selectron tube. Magnetic core memory became the dominant memory technology through the 1960s. The document then describes the main types of memory - ROM, RAM, cache memory, and flash memory. RAM is the most common type and is either DRAM or SRAM. Memory is measured in bytes, kilobytes, megabytes etc. and is stored on memory modules that fit into slots on the motherboard.
Computer Memory
- 2. Topics History of memory Memory Types of memory
- 3. History of memory In the early 1940s, memory technology mostly permitted a capacity of a few bytes. ENIAC(Electronic Numerical Integrator And Computer): Firs electronic general-purpose computer . That is capable of being reprogrammed to solve a large class of numerical problems.
- 4. Vacuum tubes. The first electronic programmable digi tal computer the ENIAC, using thousands of octal- base radio vacuum tubes could perform simple calculations involving 20 numbers of ten decimal digits
- 5. delay line memory: developed by J. Presper Eckert in the early 1940s. It is also used in digital computers. Delay line memory would be limited to a capacity of up to a few hundred thousand bits to remain efficient.
- 6. random access computer memory the Williams tube and Selectron tube originated in 1946. in 1947 Jay Forrester, Jan A. Rajchman and An Wang developed magnetic core memory which allowed for recall of memory after power loss.
- 7. random access computer memory. the Selectron was limited to 256 bits, while the Williams tube could store thousands
- 8. Magnetic core memory •It was the computer memory of choice throughout the 1960s, until it was replaced by semiconduc tor memory.
- 9. Memory . Electronic components that store instructions, data, and results Consists of one or more chips on motherboard or other circuit board Each byte stored in unique location called an address.
- 10. Memory It holds the data and instructions that the Central Processing Unit (CPU) needs. Before a program can be run the program is loaded from the storage medium into memory. It allows the CPU to direct interact with the program. Memory is a need of every computer
- 11. Memory Memory chips almost always come as part of a card called a module. Memory's usually listed with two numbers, such as 8x32 or 4x16. The first number represents the number of chips on the module. The second one tells the capacity of each individual chip, measured in megabits (Mb), or one million bits.
- 13. Types of memory 1. ROM (Read Only Memory) 2.RAM (Random Access Memory) 3.Cache 4.Flash memory
- 14. ROM stores data without electrical current; it is the ROM (Read Only Memory) or is sometimes called non-volatile memory as it is not erased when the system is switched off Read Only Memory
- 15. Types of ROM PROM (Programmable Read Only Memory) EPROM (Erasable Programmable Read Only Memory) EEPROM (Electrically Erasable Read Only Memory .
- 16. PROM Programmable read-only memory (PROM) is a blank ROM chip on which a programmer can write permanently, but once written cannot be changed or modified ROM cannot be written when the computer is running. ROM use for important program like BIOS or the firmware of a device.
- 17. PROM . Once a program has been written onto a PROM, it remains there forever.
- 18. But most ROM chips designed to be modified by users, use Erasable programmable read-only memory ( EPROM) or electrically erasable programmable read-only memory ( EEPROM).
- 19. EPROM An EPROM or erasable programmable read only memory, is a type of memory chip Once programmed, an EPROM can be erased with the help of ultraviolet light
- 20. EEPROM Electrically Erasable Programmable Read-Only Memory Type of PROM that can be erased by exposing it to an electrical charge. Similar to EPROM.
- 21. Memory How is memory measured? Term Abbreviation Approximate Size Kilobyte KB or K 1 thousand bytes Megabyte MB 1 million bytes Gigabyte GB 1 billion bytes Terabyte TB 1 trillion bytes By number of bytes available for storage
- 22. RAM Random Access Memory, can be accessed randomly. Any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.
- 23. Memory What is random access memory (RAM)? p. 195 The more RAM aThe more RAM a computer has, thecomputer has, the faster it respondsfaster it responds Also calledAlso called main memorymain memory oror primaryprimary storagestorage Most RAM isMost RAM is volatilevolatile, it is lost, it is lost when computer’swhen computer’s power ispower is turned offturned off Memory chips that can beMemory chips that can be read from and writtenread from and written to by processorto by processor
- 24. RAM RAM is mostly sold in multiples of 16 megabytes: 16, 32, 64, 128, 256, 512 and 1,024 (the same as 1GB) . DDR2 and DDR3 RAMs. DDR2 Appears in 2004 (speed: delivering bandwidth of up to 8.5 GB per second) DDR3 Appears in 2007(speed : can transfer data at rates up to 12.8 GB per second)
- 25. DDR2 DDR3 RAMs
- 26. Types of RAM There are two different types of RAM: DRAM (Dynamic Random Access Memory) SRAM (Static Random Access Memory). DRAM: Needs to be refreshed thousands of times per second while. Dynamic RAM needs to automatically refresh thousands of times per second; that's where it gets the name dynamic. Otherwise, it will forget the information it's holding.
- 27. DRAM
- 28. SRAM Does not need to be refreshed, which is what makes it faster than DRAM. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.
- 29. Memory Where does memory chips reside? Memory slots on motherboard hold memory modules memory chip memory slot dual inline memory module
- 30. Cache memory Helps speed computer processes by storing frequently used instructions and data The cache is a smaller, faster memory which stores copies of the data from frequently used main memory locations.
- 31. Cache memory When the processor needs to read from or write to a location in main memory, it first checks whether a copy of that data is in the cache. If so, the processor immediately reads from or writes to the cache, which is much faster than reading from or writing to main memory.
- 33. Flash Memory Non volatile memory can be erased electronically and rewritten similar to EEPROM. Introduced by Toshiba in 1984 Most computers use it to hold up their startup instructions Also used in many mobiles , smart phones , digital cameras and PDA
- 34. Flash memory There are two main types of flash memory. 1. NAND 2.NOR NAND type flash memory may be written and read in blocks. NOR type flash allows a single machine word(byte) to be written to an erased location or read independently.
- 36. What is capacity . Kilobyte (KB) 1 thousand Megabyte (MB) 1 million Gigabyte (GB) 1 billion Terabyte (TB) 1 trillion Petabyte (PB) 1 quadrillion Number of bytes (characters) a storage medium can hold Exabyte (EB) 1 quintillion Zettabyte (ZB) 1 sextillion Yottabyte (YB) 1 septillion
- 37. Memory Smallest unit: bit 8 bit = 1 byte 1024 byte = 1 kb (kilo byte) Each byte is able to represent 255 different number (0 to 255)