Feature
Article
by Bob Elgines
Colorado River Computer Club
This article is brought to you by the Editorial Committee of the Association of Personal Computer User Groups (APCUG), an international organization to which this user group belongs.
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Random Access Memory!
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 CORE MEMORY '50:
Pictured here is a single ferrite donut used in a core memory unit for one byte of memory. When the core is magnetized, that is equal to "one" and when it is demagnetized, that is equal to "zero." This required a lot of power, so large DC power supplies were needed, producing a lot of heat. Core memory units were built to a maximum of 48K and were used in the US until 1993. The last USAF tube type computer operating in the United States with a memory core unit was finally shut down in the summer of 1986. It was located in the Block house just outside the main gate of Luke AFB in Arizona. The computer tube type processor took up a room 40ft by 40ft with ten each 3ft by 8ft high cabinets and only 48KB of RAM to cover the South Western United States SAGE aircraft tracking system with multiple RADAR input feeds.
CHIP MEMORY '69:
To speed up computers we now write and read more than one bit at a time. Back in the sixties they decided a computer word would be a total of eight bytes of data. Some of the first memory chips were 1kb, then increasing to 4k, 16k, 32K, 64K, etc. As the late eighties came along, the IBM 286 machine had a 16 bit word (but as far as memory is talked about really two eight bit words) using 256KB individual chips directly on the mother board to a max of 1MB. Since you require a data line for each bit the data bus was increased to 16 data lines.
30-pin SIMMS '89:
They first came out with parity (requiring an extra chip for the parity bit) and then non-parity. Most of all your newer machines are capable of using non-parity (lower cost) type SIMMs. As the 386DX processor appeared, we now could move a 32-bit word around, but most programs still operate using 16-bit words at this time. Memory chips were put on separate printed circuit boards with 8 chips for no-parity and 9 chips for a parity bit location. So, for a 16-bit word machine, you would need two SIMM boards or for a 32-bit word machine, you would need four each of the SIMM boards (32/8=4).
72-pin SIMMS '95:
Of course, now with WIN 3.11 and 32-bit extensions, Win95 and WinNT, and the new programs and machines, we can use true 32-bit word operation. In other words, we can transfer 32 bits of data on the bus at any one time. This comes in handy mainly for graphics and internet operation. Otherwise, there is no difference other than you are required to have more memory chips to make this operation successful. Like, with the 8-bit word, 64KB of RAM was great, but with the 32-bit word, 16MB of RAM is great. The reason being is RAM is still counted using the old eight-bit word, why as now you need four times more places in RAM for each word (4x8 bytes = 32bytes). The 72-pin SIMMs are a 32-bit setup so your machine would allow you to change or add them one stick at a time.
EDO SIMMS '96:
For the faster Pentium processors (now up to 266 MHz with MMX) and proper mother boards, the new EDO (Extended Data output ) Simm memory boards came with an added cache chip to speed up memory access due to motherboard clock speeds, which now runs up to 75MHz.
168 pin DIMMS '97:
The new RAM boards out are called DIMMs, which is a 64-bit memory board at 66MHz (like two 72 pin SIMMs on one). In 1998 and 1999, higher speed boards arrived at 100MHz and then at 133MHz.
 184 pin DDR '01:
Some of the latest RAM arrived called DDR or PC2100 operating at 266MHz to aide in the operation of Intel's new P4 processor and AMD's 2100. Then in 2002, a higher speed DDR333 or PC2700 operating at 333MHz and DDR433 or PC3500 operating at 433MHz with CPUs over 1GHz.
184/232 pin RIMM '02:
The latest type of memory operating up to 800MHz. Fast memory is finally here bypassing Mother board speed. The type 1066 is a 16Bit, 184 pin module, and therefore must be installed as pairs. They are available up to 512MB per module.
184/232 pin RAMBUS/RDRAM '02:
The type 4800 uses RSL (RAMBUS Signaling Level) technology to achieve transfer rates exceeding 4.8GB/sec of bandwidth. They are 32-bit, 232-pin modules available up to 256MB (RDRAM). The architecture of RDRAMs allows the highest sustained bandwidth for multiple, simultaneous randomly addressed memory transactions.
The separate control and data buses with independent row and column control yield over 95% bus efficiency. The RDRAM's multi-banks configuration supports up to four simultaneous transactions.
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