RAM Types

RAM Types

Type	Characteristics
FPM (Fast Page Mode)	Older Used with 30- or 72-pin SIMM or 168-pin DIMM
EDO (Extended Data Out)	Dual-pipelined Used with bus speeds up to 66 MHz Faster than FPM RAM Used with 72-pin SIMM or 168-pin DIMM
SDRAM (Synchronous Dynamic RAM)	Dual-pipelined Used with bus speeds of 66 MHz and up One data transfer operation per clock cycle Typically used with Pentium IIs and IIIs Used with 66/100/133/150 MHz, 168-pin DIMM or 66/100/133 MHz 144-pin SO-DIMM
DDR-SDRAM (Double-Data Rate Synchronous Dynamic RAM)	Dual-pipelined Used with bus speeds of 100 MHz and up Lower power requirements than SDRAM Two data transfer operations per clock cycle Typically used with Pentium 4s and Athlons Used with 200/266/300/333/370/400 MHz, 184-pin DIMM or 266 MHz, 200-pin SO-DIMM
RDRAM (Rambus DRAM)	Used with system bus speeds of 800 to 1066 MHz Can use a 16- or 32-bit data path Requires continuity module to provide continuity between memory modules Used with 800 or 1600 MHz, 184-pin (16-bit data path) or 232-pin (32-bit data path) RIMM

Memory Installation Facts

Following are some common signs that a computer needs additional memory:

• High Hard Disk Usage: Some operating systems send data to the hard disk drive if there is not enough physical memory available. If you hear the hard drive constantly operating as you work, or if the hard drive light on the front of the system case stays illuminated for long periods of time, you may need to add more physical memory to the computer.
• Not Enough Memory Errors: If you receive Not Enough Memory or Out of Memory errors when you try to open and use more than one program at a time, you may need more physical memory. On the other hand, the DOS operating system has limitations on how memory is used. If you are receiving these kinds of errors in a DOS or Windows 3.x environment, you may need to configure the operating system to make better use of physical memory or change operating systems.

Here are some tips to remember when installing memory.

• Prevent ESD: Memory modules are very sensitive to ESD. Be sure to take proper steps to prevent ESD.
• Match Metal Types: Install memory modules that use the same types of metal for their leads as the metal in the memory slot on your system board. If you use conflicting types of metal, the connection tends to lose effectiveness over time.
• Install in the Correct Slot: Although several memory slots might be open, some system boards require that you use specific slots. Check the system board documentation for more details.
• Do Not Install Backwards: One side of the memory modules has a small key cut out of the card. This prevents the memory module from being inserted backwards into the slot.
• Check for BIOS Errors: During the Power On Self-Test, the BIOS counts the contiguous memory addresses it can find in the computer. If it does not count the proper amount of memory, you might have installed the memory incorrectly or you may have a faulty memory module. Also, if the BIOS generates an error between 200 and 299, the error is a memory error.
• Replace older, slower memory: Don't mix newer, faster memory modules with older ones. Your system will only run as fast as the slowest memory. For that reason, replace older memory modules with newer ones when you upgrade.

 

ROM Types

Type	Characteristics
ROM (Read-only Memory)	Programmed by the chip manufacturer Not erasable
PROM (Programmable Read-only Memory)	Programmed by chip manufacturer Not erasable once programmed
EPROM (Erasable Programmable Read-only Memory)	Programmed by the OEM or user Erasable by the user with ultraviolet light Re-programmable by the user after erasure
EEPROM (Electrically Erasable Programmable Read-only Memory; also known as Flash Memory)	Programmed by the chip manufacturer or user Erasable and re-programmable by the user with software (electronically) Stores data even without power Limit to how many times the data in an EEPROM chip can be flashed (modified)