PC Hardware

Tutorial Summary: Memory

The following points summarize the key concepts in this tutorial:


  • ROM is a form of nonvolatile memory that is used in PCs to hold POST commands.

  • RAM is the memory that is used by the CPU to temporarily hold data that is currently used by the system. It is cleared any time the system is powered down or rebooted.

  • RAM chips come in many sizes and shapes. It is important for the computer technician to be able to identify the different types and calculate how many chips, banks, or rows of memory modules are needed to upgrade a computer.

  • The number of SIMMs required is based on the width of the data bus.

Mapping Memory

  • Memory (RAM) is allocated to different parts of the CPU. A computer technician uses a memory map to describe how memory is allocated.

  • Hexadecimal numbers are used to identify the location of memory on a memory map.

  • MS-DOS can access only the first 1 MB of memory.

  • Several commands, such as MEM.COM, are used to identify memory allocation in a computer.

  • A computer technician must know the difference between conventional and high memory.


  1. What is hexadecimal shorthand used for?

  2. Define the following terms: conventional memory, expanded memory, extended memory, HMA, shadow RAM.

  3. Describe the difference between ROM and RAM.

  4. How many 30-pin SIMM boards are required for one bank of memory on a computer with a 486 processor?

  5. What is the difference between "write-through" and "write-back" cache?

  6. What is DRAM?

  7. Define access speed.

  8. Describe the major difference between SIPPs and SIMMs.

  9. Define cache memory.

  10. One of the differences between DRAM and SRAM is that SRAM does not have to be refreshed. What does this mean, and how does it affect the cost of each type of chip?