# Specifying SIPPs and SIMMs

When speaking of DRAM SIPPs and SIMMs, we use two values to determine how much memory a unit can hold:

• Width: 1 bit, 4 bits (a nibble), 8 bits (a byte), or 16 bits (a word), and so on.

• Depth: How deep the chip is: 256 KB, 1 MB, 4 MB, 8 MB, 16 MB, 32 MB, and so on.

By combining the depth and width, the "size" of the DRAM chip can be determined.

Here are a few points to remember when specifying DRAM:

• When upgrading memory, you add megabytes.

• When purchasing DRAM, you buy bits.

• Calculate chip size by multiplying depth by width; the result is measured in bits.

• One KB of memory is equal to 8192 bits (1024 x 8).

• One MB is equal to 8,388,608 bits (1024 x 1024 x 8).

The following table lists common DRAM module sizes.

Chip (depth x width) Number of Chips/Module Memory per Module
256 KB x 1 8 256 KB
256 KB x 4 2 256 KB
256 KB x 16 1 512 KB
512 KB x 8 1 512 KB
1 MB x 1 8 1 MB
1 MB x 4 2 1 MB
1 MB x 16 1 2 MB
2 MB x 8 1 2 MB
4 MB x 1 8 4 MB
4 MB x 4 2 4 MB

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