How Computer Systems Affect Digital Forensics | Chapter 4 from Learn Computer Forensics by William Oettinger

Understanding how computer systems are built and how they store data is foundational for every digital forensic examiner. Chapter 4 of Learn Computer Forensics (Second Edition) by William Oettinger breaks down the architecture of computer systems and examines how each component—from the boot process to partitioning—impacts forensic investigations and evidence recovery.

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The Boot Process: BIOS, UEFI, and Secure Boot

Oettinger begins by walking through the computer boot process, starting with the Power-On Self-Test (POST), then moving into BIOS or UEFI initialization, and finally handing off to the operating system.

• BIOS is the legacy firmware interface, while UEFI supports features like Secure Boot and GUID Partition Tables (GPT).
• Secure Boot ensures the system only boots trusted software, which can affect evidence recovery if improperly configured or bypassed.

Forensic examiners must understand these differences when preparing bootable forensic environments using tools like PALADIN or WinFE.

Hard Drives, SSDs, and Drive Geometry

Storage devices are critical sources of digital evidence. Oettinger explains how:

• HDDs use spinning platters and read/write heads, governed by mechanical geometry
• SSDs rely on flash memory and present challenges such as wear leveling and TRIM operations

Understanding how data is stored physically allows investigators to better interpret imaging results and recognize areas where hidden data may reside.

Partitioning Schemes: MBR vs GPT

Two main partitioning methods are explored:

• MBR (Master Boot Record) – legacy format supporting up to four primary partitions
• GPT (GUID Partition Table) – modern format allowing larger and more flexible disk structures

Investigators must identify the partitioning scheme to properly mount and analyze forensic images.

Forensic Boot Media and Secure Environments

Oettinger outlines how bootable forensic environments such as PALADIN and WinFE provide:

• Write-protected access to target devices
• Secure platforms for data acquisition without modifying evidence

These tools are essential when imaging systems that cannot be safely removed or powered down.

File Systems: FAT32 vs NTFS

A detailed comparison of file systems follows:

• FAT32 – uses a File Allocation Table to manage data, supports basic file recovery, and stores directory entries simply
• NTFS – features a Master File Table (MFT), advanced metadata handling, run lists, and non-resident file storage

Oettinger explains how forensic tools can uncover deleted data, recover hidden files, and interpret low-level disk structures within these file systems.

Hidden Storage Areas and Slack Space

Chapter 4 concludes with an in-depth look at hidden or unused spaces that often store valuable forensic data:

• Slack space – leftover space in disk clusters that may contain remnants of deleted files
• HPA (Host Protected Area) – a hidden section of the drive that can conceal malicious or sensitive data
• DCO (Device Configuration Overlay) – modifies the visible size of a disk to hide partitions from the OS

Forensic examiners must use low-level tools and disk imaging software to identify and extract information from these locations.

Conclusion

Chapter 4 underscores the importance of knowing your hardware. From understanding the boot process to uncovering data hidden deep in slack space, mastering computer systems is crucial for any digital forensic professional. This knowledge helps uncover, preserve, and interpret digital evidence in a legally defensible way.

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