Memory Basics

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Memory in computer is characterized by memory slots where RAM (random Access Memory) modules are place, ROM (Read Only Memory) as in BIOS. Memory involves few terms which are

Parity checking is a error-checking scheme and refers to the use of parity bits to check that data is accurate. The parity bit is added to every data unit (typically seven or eight bits). The parity bit for each unit is set so that all bytes have either an odd number or an even number of set bits. As quality has increased parity checking became rare.

Error Checking and Correcting (ECC) is an error detection method where check bits are generated and stored with the data. ECC can detect single- and double-bit errors

Access time is the time delay or latency between a request for data at a memory location and the requested data returned. It is measured in milli seconds (ms) or nano seconds (ns)

Bit and Byte per second – Bitrate (or bit rate, data rate or bps) is the number of bits that are conveyed or processed per unit of time and similarly Bps refers to Byte per second (or Bps) so dividing bit per second by 8 gives us Byte per second.

Non-volatile memory –  If memory can retain the stored information even when not powered and volatile memory is the memory which loses information when powered off.

Unbuffered memory or unregistered memory is RAM having no hardware register between the memory controller( it is a circuit to manages data flow from and to the main memory.) and the RAM chips. Unbuffered memory is the opposite of registered memory. Registered memory is more stable, one clock cycle slower, and more expensive than unbuffered memory. Registered memory is usually used in servers and workstations, while normal PCs usually use unbuffered memory.

Column Address Strobe latency, or CL, is the delay time between the moment a memory controller tells the memory module to access a particular memory column on a RAM memory module, and the moment the data from given location is available on the module’s output pins. In general, the lower the CAS latency, the better.

Pins – Originally the name for the “legs” on a memory module, similar to the legs (or lead) on an electronic chip. The terminology has carried over to describe the number of contacts on memory modules even when they are not pins.

Bank – A group of memory chips (not modules) that together can supply enough data bits to equal the CPU data bus but used earlier.

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