Random Access Memory (RAM)
RAM stores programs and data that are needed for the execution. It is considered volatile storage because the contents of RAM are lost when the power is switched off. RAM is also sometimes called Read-Write Memory (RWM), which is actually a more precise name. RAM needs to be writable in order for it to do its job of holding program and data.
Next to the CPU itself, RAM is the most important factor that influences computer performance. If a computer system responds slowly or accesses the hard drive constantly, then it needs more RAM.
There are many different types of RAM:
1.Dynamic RAM (DRAM): DRAM is the most basic kind of RAM which is frequently used. It stores information in cells which are etched onto a silicon wafer in an array of columns and rows. The intersection of a columns and rows constitute the address of the memory cell. Each cell contains a capacitor and a transistor. While the transistor does the switching action the capacitor correspondingly contains either no charge (0 bit) or a charge (1 bit). DRAM chips are small, simple, cheap and easy to manufacture. DRAM chips can store more information than Static (SRAM).
1.Dynamic RAM (DRAM): DRAM is the most basic kind of RAM which is frequently used. It stores information in cells which are etched onto a silicon wafer in an array of columns and rows. The intersection of a columns and rows constitute the address of the memory cell. Each cell contains a capacitor and a transistor. While the transistor does the switching action the capacitor correspondingly contains either no charge (0 bit) or a charge (1 bit). DRAM chips are small, simple, cheap and easy to manufacture. DRAM chips can store more information than Static (SRAM).
2. Static Ram (SRAM): This memory is entirely of the DRAM. Whereas, DRAM needs constant refreshment, SRAM does not require it. This is because in SRAM chips are complex. A binary cell, also called a flip-flop takes four or six transistors along with same wiring. This makes SRAM notably faster than DRAM. However, it takes more space on a chip than a DRAM cell. This is why SRAM a lot more expensive too.
| DRAM | SRAM |
|---|---|
| 1. It is Dynamic. | 1. It is Static. |
| 2. This type of memory cell contains only one transistor, hence takes less space than a SRAM cell. | 2. This type or memory cell contains four or six transistor, taking space than the DRAM cell. |
| 3. It requires constant refreshment. | 3. It Doesn't requires constant refreshment. |
| 4. It is slower. | 4. It is faster. |
| 5. It is expensive. | 5. It is more expensive. |
| 6. DRAM forms the larger system RAM space. | 6. SRAM is used to create the CPU's speed-sensitive cache. |
3. Extended Data Out RAM (EDORAM): It is faster than DRAM. It can send data even while receiving instructions for the next task. Therefore, it does not wait for the processing of the first task to finish before continuing to the next one. As soon as the address of the first bit of the first process is located, EDORAM begins looking for the next bit.
4. Video RAM (VRAM): This type of RAM is used for high-resolution displays by video adapters or 3D accelerators. It is an expensive RAM chip that is capable of performing read and write mechanisms at the same time and being accessed by two devices simultaneously. That is why, it is also known as the dual-ported RAM. Another unique feature or VRAM is that it also increases the overall speed of the video card.
5. Synchronous DRAM (SDRAM): This type of RAM synchronizes itself with the computers system clock to provide synchronization between the memory and the computer processor.
6. Double Data Rate Synchronous Dynamic RAM (DDR SDRAM): This type of RAM is similar to SDRAM except that is has higher bandwidth, which makes it very fast.
7. Ferroelectric RAM (FRAM): This memory uses a special magnetic film to store data. it has the ability to read and write data similar to DRAM, but what makes it unique is that it retains data even when power is turned off.
8. Rambus Dynamic RAM (RDRAM): RDRAM uses a Rambus In-Line memory Module (RIMM), which is fairly fast and similar in size and pin configuration to a standard Dual In-Line Memory Module (DIMM). It uses a special high speed data bus called the Rambus channel. Since EDRAM operates at high speed, it generates huge amount of heat than other types of chips. To reduce this heat, Rambus chps are fitted with a heat spreader.
Just like smaller versions of Dual In-Line Memory Module (DIMMs), there are also SO-RIMMs, designed for notebook computers.
Read Only Memory (ROM)
Read Only Memory (ROM) is an essential requirement to load the computer. Hence, it can be said that it is the most important type of memory in the computer system. ROM integrated circuits or chips are programmed with specifies data and information at the time of their manufacture itself. In other words. ROM is a type of computer memory on which the data is prerecorded, mostly with system-level programs. The most common example is the system BIOS program, which is stored in a ROM called the system BIOS ROM. BIOS ROM contains the instructions that allow the computer operating system and peripherals to communicate with each other.
ROM type of memory is normally read, as opposed to RAM, which can be both read and written. There are two main reasons why ROM is used for certain important functions within the computer:
1. Performance: ROM retains its contents even when the computer is turned off. A ROM can be removed form the PC, stored for an indefinite period of time, and then replaced. It retains all the data stored in it permanently. For this reason it is called no-volatile storage. A hard disk is also no-volatile, for the same reason, but regular RAM in not.
2. Security: The fact that ROM cannot easily be modified provides a measure of security against accidental changes to its contents.
ROM works quite differently form RAM. Though it has rows and columns like RAM, where RAM uses transistors to turn on or off access to a capacitor at each intersection ROM uses a diode to connect the lines if the value is 1. If the value is 0, then the lines are not connected at all.
Despite the fact that ROM contents cannot be changed, there are times when changing its contents can be very useful. There are some ROM variants that can be changed under certain circumstances. Let us now familiarize ourselves to various types of ROM.
3. Programmable ROM (PROM): PROM is programmed on a blank chip. PROM is programmed using special equipment called PROM programmer or PROM burner, it can be written to, but only once. It is irreversible, meaning that its contents cannot be altered,. However, there are a few selected memory locations that can be changed by applying electric signals. This variant of PROM is called Electrically Alterable PROM (EAPROM).
4. Erasable Programmable ROM (EPROM): An EPROM is a variant of ROM that can be erased and reprogrammed. A little glass window is installed on the top of the ROM package through which one can actually see the chip that holds the memory. Another use of this window is that ultraviolet light of a precise frequency can be passed through this window for a specified period of time to erase the contents stored in EPROM and reprogram it again. A special device called a PROM programmed or PROM burner is used or write and erase an EPROM.
5. Electrically Erasable Programmable ROM (EEPROM): Another adaptations of ROM is EEPROM that can be erased using electrical charges under software control. EEPROM requires data to be written of erased one byte at a time This is the most flexible type of ROM, and is now commonly used for holding BIOS programs.
6. Flash ROM (FROM): Flash ROM is a special type of EEPROM chip that can be erased and reprogrammed. But, the difference between the two is that, whereas EEPROM functions byte by byte, flash memory functions in blocks. Therefore, it is much faster than EEPROM.
A regular ROM chip is placed on the motherboard.
There are many types of materials that are used to make ROM chips:
- Hardwired
- Magnetic
- Transistors-Bipolar or MOS
- Fusible links
ROM chips are designed to perform significant and cannot be changed. This is inflexible and so regular ROMs are only used generally for programs that are static and mass-produced. This product is equivalent to CD-ROM software commercially available.
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