Reading and chips

One f the most  Intermediating   aspect of trying to buy extra RAM in the way that chips,  SIPs and SIMMs are described  in catalogues an manuals. Part of the problem is due to each manufacturer assigning their one product codes to each type of chip they produce. The assignment is fairly  arbitrary and so  you shouldn’t expect too much sense in the sort of numbers marked on a chip but they can provide a general guidelines to the chip’s type.
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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