A+ Certification: Part 2 – Hardware: System Architecture

Section Objectives

After you complete this section you will:

Understand what the BIOS and CMOS are.

Understand the different types of Memory.

Understand the different memory package types.

Be aware of RAM’s integral part of your computer system.


What is the BIOS?

The BIOS (Basic Input Output System) is the chip that contains low level software for configuring the system’s capabilities and communicating with the hardware. The BIOS previously was stored in the ROM, though most present day computers have the BIOS stored in EEPROM, an electronically erasable programmable ROM. The BIOS communicates between the software and the hardware so fewer conflicts present themselves.

BIOS Operation

When you first enter setup on a computer, you see many options for configuring your computer. Typical options include the automatic detection of IDE drives, option to enable/disable the processor cache, Plug’N’Play feature detection, password protection, time/date settings, IRQ settings, and more.

Typically, the BIOS stores its configurations in the CMOS (Complementary Metal-Oxide Semiconductor). The CMOS is powered by a small battery so it can retain its settings after the power is turned off. The CMOS is usually not upgradeable, but the battery used to power it is usually easily upgradeable.

Troubleshooting and the BIOS

Since the BIOS contains the low level software controlling the computer, you may need to replace it in earlier PCs if you have to upgrade the hard drive.

If you continually lose your settings in between power cycles of your machine, your CMOS battery may need to be replaced. This can be found on the motherboard and is typically a standard battery you can get replaced at most computer shops or electronics stores.

Example Screenshots of Different BIOSs (Click to open larger in a new window)



ROM (Read-Only Memory) is a form of non-volatile memory. Non-volatile memory keeps its contents even there is no power. Read-only memory is just that, read only, it cannot be written to. The computer ROM contains the setup program and POST (Power On Self Test) software.


RAM (Random Access Memory) is a volatile type of memory which loses its information when power is not present. RAM is where your software and data is stored when your computer is on and you are actively using or accessing them.

There are many different types of RAM common in today’s PCs, though the different types fit into one of these two categories:

DRAM – Dynamic RAM. Dynamic RAM needs to be refreshed thousands of times a second.

SRAM – Static RAM. Does not need to be refreshed like DRAM, which makes it faster. More expensive than DRAM.


PROM (Programmable ROM) is a programmable type of ROM. It cannot be erased or changed once it is recorded.


Eraseable PROM can be erased using a UV light on a special window on the chip. This chip can be reprogrammed.


Electronically Erased PROM can be erased using a special electrical charge. Chips can then be reprogrammed after erased. Most modern day BIOSs are stored in EEPROM.


Video RAM is used on video cards to display video to the monitor. VRAM is dual-ported, it can be read from and written to at the same time from two different devices. VRAM is a very fast type of memory used on most video cards.


WRAM (Windows RAM) is a dual-ported type of memory – meaning you can read and write to the RAM at the same time from different devices. It was developed to be an extremely fast graphics RAM. The Windows in Windows RAM is the large “windows”, or chunks, of memory that can be written to or read from at a given time.


SGRAM (Synchronous Graphics RAM) is synchronized with the system clock. Unlike WRAM, SGRAM is single-ported. It syncs itself to the system clock and can run at speeds up to 100 MHz. It is a type of DRAM.


RDRAM, or Rambus DRAM, is a type of DRAM developed by Rambus Inc. which allows access to the memory at 800 MHz, breaking the current 100 MHz barrier.

Cache Memory

Cache memory is memory used to cache CPU instructions. L1 is cache memory that is located on the CPU. L2 is cache memory located outside the CPU.


Dual Inline Package is an older RAM type used in older systems.

Memory Packages


Dual In-line Pin Packages – mainly used in EEPROMs.


Single In-line Pin Packages


Single In-line Memory Modules. Typically found in older systems in 30 or 72 pin chips. 32-bit data path. Pentium processors require s 64-bit data path, so you need to install SIMMs in pairs (e.g. 2 32MB SIMMs).


Dual In-line Memory Modules. Most common type of system memory, usually 168 pin. 64-bit data path, can be installed in single chips.


Small Outline DIMM. A type of laptop or PDA memory, 144 pin.

RAM and Your Computer


RAM is broken up into DOS memory “sections.” The first 640 Kb of memory is Conventional Memory, which is used to load DOS, run programs, and load drivers. DOS is loaded in the first 64K of memory.

Above 640 Kb, but below 1024 Kb, is Upper Memory, also called Reserved Memory. 640 Kb – 768 Kb is Video RAM, 768 Kb – 960 Kb is for BIOS and RAM buffers, and 960 Kb – 1024 Kb is Motherboard BIOS.

Above 1024 Kb is Extended memory. High Memory Area (HMA) is the first 64 Kb of Extended memory. Extended memory is mainly used by Windows programs.

Expanded memory is sometimes used by DOS programs and is available up to 32 MB. It is swapper in 16 Kb pages (addresses in pages of 16 Kb).

In DOS, the MEM.EXE program allows you to determine how memory is being used by DOS. It has several switches, the important ones are highlighted here: /? the help switch, /C the classify switch – gives a report of how memory is used, /D the debug switch – details the first 640KB of memory, /F the free memory switch, shows all free memory blocks in the first 640KB of memory, /M (module) the module switch, shows the starting addresses of the data, program, and how much memory is allocated, and /P the pause switch, displays the output one page at a time.

To use upper memory, you need to make sure the upper memory device driver, EMM386.EXE is invoked in CONFIG.SYS and DOS=UMB is there also.

DOS=HIGH loads DOS into HMA.

Device=HIMEM.SYS is the extended memory device driver.

A Parity Error indicates a problem with RAM. Parity is a simple form of error checking and is used to check RAM.

After you have studied this section you should:

Understand what the BIOS and CMOS are.

BIOS, or Basic Input Output System is the low level software which handles the basic functions of the computer. The CMOS is the area where the BIOS settings are stored.

Understand the different types of Memory.

Understand the different memory package types.

Be aware of RAM’s integral part of your computer system.

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