Basics of Computer Hardware

Computer Basics

A computer is an electronic device that manipulates information, or "data." It has the ability to store, retrieve, and process data. You can use a computer to type documents, send email, and browse the internet. You can also use it to handle spreadsheets, accounting, database management, presentations, games, and more.

All types of computers consist of two basic parts:

Hardware is any part of your computer that has a physical structure, such as the computer monitor or keyboard.

Software is any set of instructions that tells the hardware what to do. It is what guides the hardware and tells it how to accomplish each task. Some examples of software are web browsers, games, and word processors such as Microsoft Word.

What are the Different Types of Computers?

Understanding Operating Systems

An operating system is the most important software that runs on a computer. It manages the computer's memory, processes, and all of its software and hardware. It also allows you to communicate with the computer without knowing how to speak the computer's "language." Without an operating system, a computer is useless.

The Operating System's Job

You've probably heard the phrase boot your computer, but do you know what that means? Booting is the process that occurs when you press the power button to turn your computer on. During this process (which may take a minute or two), the computer does several things:

It runs tests to make sure everything is working correctly.
It checks for new hardware.
It then starts up the operating system.

Once the operating system has started up, it manages all of the software and hardware on the computer. Most of the time, there are many different programs running at the same time, and they all need to access your computer's Central Processing Unit (CPU), memory, and storage. The operating system coordinates all of this to make sure that each program gets what it needs. Without the operating system, the software wouldn't even be able to talk to the hardware, and the computer would be useless.

Microsoft Windows

Microsoft created the Windows operating system in the mid-1980s. Over the years, there have been many different versions of Windows, but the most recent ones are Windows 8 (released in 2012), Windows 7 (2009), and Windows Vista (2007). Windows comes preloaded on most new PCs, which helps to make it the most popular operating system in the world.

Windows - Boot process

BIOS: performs Power On Self Test (POST)
BIOS: BIOS Bootstrapping loads MBR from the boot device specified/selected by the BIOS

MBR: contains a small amount of code that reads the partition table, the first partition marked as active is determined to be the system volume
MBR: loads the boot sector from the system volume

BOOT SECTOR: reads the root directory of the system volume at loads NTLDR

A boot sector or boot block is a region of a hard disk, floppy disk, optical disc, or other data storage device that contains machine code to be loaded into random-access memory (RAM) by a computer system's built-in firmware. The purpose of a boot sector is to allow the boot process of a computer to load a program (usually, but not necessarily, an operating system) stored on the same storage device.

NTLDR: reads BOOT.INI from the system volume to determine the boot drive (presenting a menu if more than 1 entry is defined)

NTLDR: loads and executes NTDETECT.COM from the system volume to perform BIOS hardware detection

NTLDR: loads NTOSKRNL.EXE, HAL.DLL, BOOTVID.DLL (and KDCOM.DLL for XP upwards) from the boot (Windows) volume

NTLDR: loads \WINDOWS\SYSTEM32\CONFIG\SYSTEM which becomes the system hive HKEY_LOCAL_MACHINE\System

NTLDR: loads drivers flagged as "boot" defined in the system hive, then passes control to NTOSKRNL.EXE

NTOSKRNL.EXE: brings up the loading splash screen and initializes the kernel subsystem

NTOSKRNL.EXE: starts the boot-start drivers and then loads & starts the system-start drivers

NTOSKRNL.EXE: creates the Session Manager process (SMSS.EXE)

SMSS.EXE: runs any programs specified in BootExecute (e.g. AUTOCHK, the native API version of CHKDSK)

SMSS.EXE: processes any delayed move/rename operations from hotfixes/service packs replacing in-use system files

SMSS.EXE: initializes the paging file(s) and the remaining registry hives

before this step completes, bugchecks will not result in a memory dump as we need a working page file on the boot (Windows) volume

SMSS.EXE: starts the kernel-mode portion of the Win32 subsystem (WIN32K.SYS)
SMSS.EXE: starts the user-mode portion of the Win32 subsystem (CSRSS.EXE)
SMSS.EXE: starts WINLOGON.EXE

WINLOGON.EXE: starts the Local Security Authority (LSASS.EXE)

WINLOGON.EXE: loads the Graphical User Identification and Authentication DLL (MSGINA.DLL by default)

WINLOGON.EXE: displays the logon window

WINLOGON.EXE: starts the services controller (SERVICES.EXE)

at this point users can logon

SERVICES.EXE: starts all services markes as automatic

NOTES:

The SYSTEM volume is the partition from which the boot process starts, containing the MBR, boot sector, NTLDR, NTDETECT.COM & BOOT.INI

The BOOT volume is the partition which contains the Windows folder - this can be a logical partition

Example 1:
2 hard disks, 0 and 1
Disk 0, partition 0 is the SYSTEM volume
Windows is installed to "D:" which is disk 1, partition 0 [even if disk 0 has an extended & logical partitions] - this is the BOOT volume
- if either disk fails or is removed, Windows cannot boot

Example 2:
1 hard disk, 2 partitions
Disk 0, partition 0 is the SYSTEM volume
Disk 0, partition 1 is the BOOT volume [D:]
- add another disk to the system and create a partition on it, this becomes D: and Windows will not boot [disk 0, partition 1 now becomes E:]

Disk partitioning

Disk partitioning is the act of dividing a hard disk drive (HDD) into multiple logical storage units referred to as partitions, to treat one physical disk drive as if it were multiple disks, so that different filesystems can be used on each partition.

Primary partition

A primary partition contains one file system. In DOS and all versions of Microsoft Windows systems, what Microsoft calls the system partition was required to be the first partition. All Windows operating systems from Windows 95 onwards can be located on ( almost ) any partition, but the boot files (io.sys, bootmgr, ntldr, etc.) must be on a primary partition.

Extended partition

An HDD may contain only one extended partition; the extended partition can be subdivided into multiple logical partitions. In DOS/Windows systems, each logical partition may then be assigned an additional drive letter.

Benefits of multiple partitions

Creating more than one partition has the following advantages:

Separation of the operating system (OS) and program files from user files. This allows image backups (or clones) to be made of only the operating system and installed software.
Having a separate area for operating system virtual memory swapping/paging.
Keeping frequently used programs and data near each other.
Having cache and log files separate from other files. These can change size dynamically and rapidly, potentially making a file system full.
Use of multi-boot setups, which allow users to have more than one operating system on a single computer. For example, one could install Linux, BSD, Mac OS X, Microsoft Windows or other operating systems on different partitions of the same HDD and have a choice of booting into any compatible operating system at power-up.
Protecting or isolating files, to make it easier to recover a corrupted file system or operating system installation. If one partition is corrupted, other file systems may not be affected.