"Out Of Memory Error"

Even with large amounts of RAM installed (above 512mb)
- unable to open an MS-DOS session
- The computer may stop responding

Cause

The Windows 32-bit protected-mode cache driver (Vcache) determines the maximum cache size based on the amount of RAM that is present when Windows starts. Vcache then reserves enough memory addresses to permit it to access a cache of the maximum size so that it can increase the cache to that size if needed. These addresses are allocated in a range of virtual addresses from 0xC0000000 through 0xFFFFFFFF 3gb-4gb

On computers with large amounts of RAM, the maximum cache size can be large enough that Vcache consumes all of the addresses in the system arena, leaving no virtual memory addresses available for other functions such as opening an MS-DOS prompt

Computer memory or address errors

Memory mismatch error
Memory parity interrupt at xxxxx
Memory address error at xxxxx
Memory failure at xxxxx, read xxxxx, expecting xxxxx
Memory verify error at xxxxx

Cause
Indicates a physical memory module error

Memory Parity Error (or Parity Check)

If it crashes as soon as you turn it on, you are probably trying to run non-parity memory in a parity system

PC does not detect all installed

- Your computer accepts only single-banked memory and you have installed dual-banked, the computer will read only half the memory on the module. Sometimes the computer will accept only modules containing memory chips with specific organizations. e.g  VX chipset doesn't work well with 64 Mbit chips.

Cause

- Your computer may have three sockets of RAM, each of which can hold a 128MB module. If you filled every socket with 128MB, you would have 384MB of memory. However, your computer support a maximum of 256MB.

201 Error Message  

This indicates there is a RAM failure

Soft-memory errors      

Soft memory errors are the errors that are caused by the infrequent glitches in the operation of the system. These errors can be controlled just by restarting the system

Hard-memory errors   

Hard memory errors are the permanent physical errors and that requires that memory units should be checked properly and replaced

ROM

This is read-only memory, memory that can only be read, but cannot be written to. ROM is used in situations where the data must be held permanently.
Programmable ROM(PROM)
A blank ROM chip that can be written to, but once only.
Erasable Programmable ROM (EPROM)
This is just like PROM, except that you can erase the ROM by shining a special ultra-violet light into a sensor atop the ROM chip for a certain amount of time wiping the data to be rewritten.
Electrically Erasable Programmable ROM (EEPROM)
Also called flash BIOS. This ROM can be rewritten through the use of a special software program. 

RAM (Random Access Memory)

Static RAM (SRAM)
This RAM will maintain it’s data as long as power is provided to the memory chips. It does not need to be re-written periodically. In fact, the only time the data on the memory is refreshed or changed is when an actual write command is executed.

Fast Page Mode DRAM (FPM DRAM)
Slower running memory with an access time of 120 ns

Extended Data Out DRAM (EDO DRAM)
Allows one access to begin while another is being completed with a performance increase of around 30%. EDO DRAM must be properly supported by the chipset. EDO RAM comes on a SIMM. EDO RAM cannot operate on a bus speed faster than 66MHz

Dynamic RAM (DRAM)
DRAM must be continually re-written in order for it to maintain its data. This is done by placing the memory on a refresh circuit that re-writes the data several hundred

Async SRAM
An older type of SRAM used in many PC’s for L2 cache. It is asynchronous, meaning that it works independently of the system clock. This means that the CPU found itself waiting for info from the L2 cache.
Sync SRAM
This type of SRAM is synchronous, meaning it is synchronized with the system clock. 
Pipeline Burst SRAM
SRAM requests are pipelined, meaning larger packets of data resent to the memory at once, and acted on very quickly. 

Burst EDO DRAM (BEDO DRAM)

Larger blocks of data were sent to the memory at a time, and each “block” of data not only carried the memory address of the immediate page, but info on the next several pages. Therefore, the next few accesses would not experience any delays due to the preceding memory requests. This technology increases EDO RAM speed up to around 10 ns, but it did not give it the ability to operate stably at bus speeds over 66MHz. 

Synchronous DRAM (SDRAM)

Synchronous speed, meaning that it is directly dependent on the clock speed of the entire system. Standard SDRAM can handle higher bus speeds. In theory, it could operate at up to 100MHz, although it was found that many other variable factors went into whether or not it could stabily do so. To get around the variability, Intel created the PC100 standard. The PC100 standard ensures compatibility of SDRAM subsystems with Intel’s 100MHz FSB processors. The new design, production, and test requirements created challenges for semiconductor companies and memory module suppliers. SDRAM chips must be used in conjunction with a correctly programmed EEPROM on a properly designed printed circuit board. The shorter the distance the signal needs to travel, the faster it runs. For this reason, there were additional layers of internal circuitry on PC100 modules.

RAMBus DRAM (RDRAM)

Developed by Rambus, Inc. and endorsed by Intel as the chosen successor to SDRAM. RDRAM narrows the memory bus to 16-bit and runs at up to 800 MHz. Since this narrow bus takes up less space on the board, systems can get more speed by running multiple channels in parallel. Despite the speed, RDRAM has had a tough time taking off in the market because of compatibility and timing issues. Heat is also an issue, but RDRAM has heatsinks to dissipate this. They are also very expensive

DDR-SDRAM 2 (DDR2)

 It features several advantages over conventional DDR-SDRAM (DDR), with the main one being that in each memory cycle DDR2 now transmits for 4 bits of information from logical (internal) memory to the I/O buffers. standard DDR-SDRAM only transmits 2 bits of information each memory cycle. Because of this, normal DDR-SDRAM requires the internal memory and I/O buffers to both operate at 200MHz to reach a total external operating speed of 400MHz. Due to DDR2’s ability to transmit twice as many bits per cycle from logical (internal) memory to the I/O buffers (formally known as 4 bit prefetch), the internal memory speed can actually run at 100MHz instead of 200MHz, and the total external operating speed will still be 400MHz.