The first part of a chip’s part number usually indicated the amount and organization of the memory that the chip provides. The same amount of memory can be organized in many different ways. For example a chip that stores 1Mbit can be arranged to provide 128Kx8bits (i.e 128Kbytes), 256Kx4bits or 1Mx1bit of storage. As most computers can only work with memory locations that can store a complete byte, The organization of the chip indicates the smallest number that can be used to increase memory capacity. For example , You could use one 128Kx8bit chip to increase memory by 128Kbytes, but you would need at least two 256Kx4bit chips (i.e 256KBytes) and eight Mx1bit chips (i.e 1 Mbyte). (The ignores the complication of needing a parity bit and memory banks, see later.)
The final digits of chip’s part number generally give its speed in nano-seconds but often leaving out or adding in extra zeros . For example, The product code for an 80ns chip might end in -80, -08 or just -8 as the manufactures choose!
Often you will find chips listed simply by their organization and speed. For example , 256Kx4 120ns DRAM, 1Mx9 80ns SIMM 256Kx1 100ns SIP ect.. On other occasions you will find their full part numbers quoted. For example , a 41256-80 is a 256Kx1bit 80ns DRAM, 41464-12 is a 64Kx4bit 120ns DRAM and a p21010-08 is a 1Mx1bit 80ns DRAM. Form these examples you can see that there is some connection between part numbers and chip types - but not enough to be certain without looking them up! If you are at all in doubt about the type of memory that you machine needs then check its manual or contact one of the specialist memory supplies listed at the end of this all posts.
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