Saifurs Spoken Vocabulary.

Lesson 5 : Memory

5.1. Learning Objectives
On completion of this lesson you will be able to describe :
i) Different memory hardware
ii) Different types of memory organization (i.e., SRAM, DRAM, SDRAM).

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5.2. Introduction

The PC must have main memory. Main memory is high-speed memory that the CPU can read from or write to. "High speed" means, less than a microsecond to read/write. The other name for such memory is RAM, Random Access Memory-a particular kind of chip on circuit boards.

5.3. Different Memory Hardware

Memory is easy to pick out on a circuit board. It's packaged either as a "bank" of eight or nine small chips, or it's a mini-circuit board with several square chip mounted on it, called a SIMM (Single Inline Memory Module). Memory is always organized into banks either eight or nine discrete chips, or a SIMM. Most motherboards have room for four banks of memory. As each SIMM is the equivalent of nine chips built in single independent card, SIMMs make replacing bad memory easier.

RAM chips are distinguished by their following characteristics:

i) Package type, which can be:
ii) DIPs, which are normal looking chips. DIP means Dual
Inline Package. It is just a simple IC with two sets of legs inline. These ICs are directly inserted in sockets on the motherboard. Laptop and old 8088 to 386 computers use this package.
i) Single Inline Pin Packages, or SIPPs (a small circuit board with pins across its bottom).
ii) Single and Double Inline Memory Modules (SIMMs and DIMMs respectively), which are small circuit boards with an edge connector across the bottom.
iii) PCMCIA cards. This package is used in laptop computers. In this package the memory is built in a card which is inserted in the PCIMCIA slots of laptop computers.
iv) Various proprietary vendor-specific chip packages.
v) Access speeds, measured in nanoseconds. Common access times are 60, 70, 80, 90, and 100ns for normal memories, and as low as 8 ns for expensive high-speed memories. Lower numbers are faster.