The Computer Memory
Fig 1. Computer Memory
Memory in computers is very important, but many people do not recognize the role it plays. Memory is the workspace for the computer’s processor. It is a temporary storage area where the programs and data being operated on by the processor must reside. Memory storage is considered temporary because the data and programs remain there only as long as the computer has electrical power or is not reset. Before being shut down or reset, any data that has been changed should be saved to a more permanent storage device (usually a hard disk) so that it can be reloaded into memory in the future. Failure to do this you will loose all your unsaved work.
Memory is often referred as RAM, short for Random Access Memory. Memory is called RAM because you can randomly (as opposed to sequentially) access any location in memory. Read-only memory (ROM), for example, is also randomly accessible, yet is usually differentiated from the system RAM because it maintains data without power and can’t normally be written to.
In computers, memory is generally divided into two:
Memory is often referred as RAM, short for Random Access Memory. Memory is called RAM because you can randomly (as opposed to sequentially) access any location in memory. Read-only memory (ROM), for example, is also randomly accessible, yet is usually differentiated from the system RAM because it maintains data without power and can’t normally be written to.
In computers, memory is generally divided into two:
- Random Access Memory (RAM)
- Read Only Memory (ROM)
Random Access Memory (RAM)
Computers and other electronic devices make use of RAM for temporally storage of data and programs in use. There are two different types of RAM, DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory).
DRAM
Dynamic RAM (DRAM) is the type of memory chip used for implementing most of the main memory in a modern PC. The memory cells in a DRAM chip make use of tiny capacitors that retain a charge to indicate a bit (1, or 0 depending on the charge). DRAMs use only one transistor and capacitor pair per bit, which makes them very dense, offering more memory capacity per chip than other types of memory.
Advantages
SRAM stands for static RAM, which is so named because it does not need the periodic refresh rates like DRAM. Because of how SRAMs are designed, not only are refresh rates unnecessary, but SRAM is much faster than DRAM and much more capable of keeping pace with modern processors. It is used to implement cache memories that need to transfer data at a very high speed.
Computers and other electronic devices make use of RAM for temporally storage of data and programs in use. There are two different types of RAM, DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory).
DRAM
Dynamic RAM (DRAM) is the type of memory chip used for implementing most of the main memory in a modern PC. The memory cells in a DRAM chip make use of tiny capacitors that retain a charge to indicate a bit (1, or 0 depending on the charge). DRAMs use only one transistor and capacitor pair per bit, which makes them very dense, offering more memory capacity per chip than other types of memory.
Advantages
- It is very dense, meaning you can pack a lot of bits into a very small chip
- It is inexpensive, which makes purchasing large amounts of memory affordable.
- It is slow because it requires refreshing.
- Fast Page Mode DRAM (FPM DRAM)
- Burst Extended Data Out RAM (BEDO DRAM)
- Extended Data Out RAM (EDO DRAM)
- Synchronous DRAM (SDRAM)
- Double Data Rate DRAM (DDR SDRAM)
- Rambus DRAM (RDRAM)
SRAM stands for static RAM, which is so named because it does not need the periodic refresh rates like DRAM. Because of how SRAMs are designed, not only are refresh rates unnecessary, but SRAM is much faster than DRAM and much more capable of keeping pace with modern processors. It is used to implement cache memories that need to transfer data at a very high speed.
Fig 2. An example of ROM
Source: wikipedia
READ ONLY MEMORY (ROM)
This is the other type of memory used in computers. Read-only memory, or ROM, is a type of memory that can permanently or semi-permanently store data. It is called read-only because it is either impossible or difficult to write to. ROM also is often referred to as nonvolatile memory because any data stored in ROM remains there, even if the power is turned off. Thus, ROM is an ideal place to put the PC’s startup instructions—that is, the software that boots the system.
This is the other type of memory used in computers. Read-only memory, or ROM, is a type of memory that can permanently or semi-permanently store data. It is called read-only because it is either impossible or difficult to write to. ROM also is often referred to as nonvolatile memory because any data stored in ROM remains there, even if the power is turned off. Thus, ROM is an ideal place to put the PC’s startup instructions—that is, the software that boots the system.
Fig 3. EPROM with a quartz window
Examples of ROMs
Read Only Memory (ROM) – This is a type of ROM manufactured with the binary data (0s and 1s) already programmed or integrated into the die. The data can not be changed.
Programmable Read Only Memory (PROM) – A PROM is a type of ROM that is blank when new and that must be programmed with whatever data you want.
Erasable Programmable Read Only Memory (EPROM) –This is a type of ROM that is erasable. To erase the contents you subject it to a strong source of UV light which penetrates through the quartz window on the top. Then new data can be entered into it again.
Electrically Erasable Programmable Read Only Memory (EEPROM) – This type of ROM is also called flash PROM. It is a PROM whose data can be erased in situ using electricity, no special equipment is required.
Read Only Memory (ROM) – This is a type of ROM manufactured with the binary data (0s and 1s) already programmed or integrated into the die. The data can not be changed.
Programmable Read Only Memory (PROM) – A PROM is a type of ROM that is blank when new and that must be programmed with whatever data you want.
Erasable Programmable Read Only Memory (EPROM) –This is a type of ROM that is erasable. To erase the contents you subject it to a strong source of UV light which penetrates through the quartz window on the top. Then new data can be entered into it again.
Electrically Erasable Programmable Read Only Memory (EEPROM) – This type of ROM is also called flash PROM. It is a PROM whose data can be erased in situ using electricity, no special equipment is required.
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